Newsletter in Acrobat format

Contents
1.0 Transplant Diseases
1.1 Vegetable seed health important to a good start
1.2 Contents
2.0 Planning ahead
2.1 Transplanters
2.2 Diseases of Vegetable Transplants
2.3 Part 2: Crucifers
2.4 Diseases of Vegetable Transplants, Part 3, Tomatoes and Peppers
2.5 Disease of vegetable transplants. Part 4: Vine Crops
2.6 Vegetable seedling Disorders
2.7 Transplant Diseases
2.8 Transplant Diseases
2.9 Treating Transplants Right
2.10 Tomato Transplant Diseases
2.11 Damping-Off of Cole Crops
2.12 Rain and Plant Disease
2.13 Seedling Diseases of Vegetable Crops
2.14 Snap Beans
2.15 Sweet Corn
2.16 Seedling Diseases of Vegetable Crops
2.17 Germination and Care of our Seedlings
2.18 Vegetable Culture and Management in a Wet year
2.19 Effect of Transplant tray type and Tomato Cultivar on the Incidence of Fusarium Crown and Root Rot in Tomato Transplants
2.19.1 Diseases that Affect Vegetables after Trans-planting
2.19.2 Sterilization and Sanitation of Flats
3.0 Phomopsis on Eggplant
3.1 Phomopsis Blight of Eggplant
3.2 Seed (hot water) Treatments
4.0 Rhizoctonia
4.1 Rhizoctonia Seedling Blight
4.2 Vegetable Diseases to Watch for
4.3 Cool Wet Soils and Problems with Damping-Off Root Rots and Seed Decay

Hawai‘i Cooperative Extension Service
College of Tropical Agriculture & Human Resources · University of Hawai‘i at Manoa · U.S.D.A. Cooperating
VEGETABLE CROPS UPDATE
Volume 7 March 1997 No. 1

Articles on transplant diseases and related topics from Illinois , Indiana, Pennsylvania, Texas, Florida, California, and Hawaii
extension newsletters and publications.
Transplant Diseases
1. Veggie seed health pg. 1-2
2. Transplanters pg. 2
3. Transplant diseases pg. 2-11
4. Crucifers, tomato,
peppers, melons pg. 3-5
5. Damping-off pg. 6
6. Rain and disease pg. 6, 8, 11
7. Snap bean, sweet corn pg. 6
8. Germination pg. 7
9. Seed treatments pg. 9
VEGETABLE SEED HEALTH IMPORTANT TO A
GOOD START
Dr. Frank Killebrew, Extension Plant Pathologist
Vegetable crop producers are fully aware that trying to
figure out what type of early season growing conditions
to expect is most often a “Best guess.” So the best rule-of-thumb
is to get started right in the hope that the weather
will cooperate. One of the best ways to reduce the chances
for early season problems is to use healthy seeds.
Seed selection is an important consideration for mid-south
vegetable producers for several reasons. One of the
most important has to do with plant diseases, since our
southern climate, with its frequent periods of humid con-ditions
during the growing season, favors the development
of many fungal, bacterial, and viral problems that may be
carried over through infected seeds. Thus, it is generally
unwise to save seeds from season to season.
Vegetable producers should purchase seed each year
from dealers who have a reputation for selling high qual-ity,
disease-free seed. Certified seed should be used when-ever
available. Examples of seed-borne diseases that can
cause severe damage when conditions are favorable are
anthracnose of lima beans, early blight of tomatoes, mo-saic
virus of southern peas, bacterial blights of beans, black
rot of cabbage, and leaf spots of turnip and mustard greens.
To help prevent diseases of this type, your seedsman will
have available seeds that have been produced under strin-gent
guidelines to insure that seeds are free from diseases.
Often seeds originate from dry regions, such as the west-ern
United States, where diseases are less common.
To help prevent diseases of this type, your seedsman will have
available seeds that have been produced under stringent guidelines
to insure that seeds are free from diseases. Often seeds originate
from dry regions, such as the western United States, where dis-eases
are less common.
After good seed have been selected, the next step is to make
sure the seeds are properly treated with fungicides. Seeds from
dealers are often pre-treated (denoted by a reddish or green color)
with fungicides such as captan or thiram for control of seed decay
and damping-off diseases. The use of treated seeds is especially
worthwhile when seeds are to be planted in the early season in
cool, wet soils, conditions which are favorable for development of
seedling diseases. Fungicides applied to seeds reduce seed rot and
give some protection from seedling disease during early stages of
seedling development.
Growers who have “homegrown” untreated seeds can easily
carry out their own fungicide seed treatment. Large seeded crops
such as corn or beans can be treated by placing seed and fungicide
in a gallon container (use a pint container for smaller seeds) and
gently shaking or rotating the container until all seeds are evenly
coated with fungicide. As little as 1/2 to 1 teaspoonful of captan or
thiram per pound of seed may be all that is needed to accomplish
this. Be sure to wash equipment and hands after handling fungi-cide
and treated seeds. Treated seeds should be planted promptly.
Continues, page 2

VEGETABLE SEED HEALTH IMPORTANT TO A
GOOD START
continued from page 1
Growers who are interested in a “Chemical-free” alterna-tive
to fungicide treatment might want to try a hot-water
soak. This technique may be used on tomato seeds and cab-bage
seeds just before planting to destroy many disease
causing microorganisms carried on and within seeds. Seeds
should be soaked at 122 degrees F for 25 minutes. When
using this technique, use a large quantity of water with some
type of agitator to keep the water temperature as uniform
as possible. Note: water temperatures in excess of that rec-ommended
may reduce the percentage of seed germina-tion.
Lower temperatures will not kill the disease microor-ganisms.
Immediately after this heat treatment, seed should
be plunged into cold water, removed, and planted promptly.
(Michael D. Orzolek, Peter A. Ferretti, Penn St. Horticul-ture
Vegetable Newsletter, Vol. 8, No. 5, May 1996)
Planning Ahead
Transplanters
“Many small vegetable farmers think using transplants
and transplanters is too expensive or complicated, but
there are good reasons to take another look. Transplanters
attach to the back of a tractor on a three-point hitch or
toolbar, or are pulled. They can plant from one to 16 or
more rows at a time. One or two people feed the plants
into the machine’s plant pockets. Often a water tank
mounted on the tractor waters and fertilizes the plants
continuously or intermittently. The transplanter performs
five functions:”
1. Opens the furrow
2. Meters the plant
3. Places the plant
4. Covers the plant
5. Firms the soil around the plant.
“A new single-row transplanter costs about $1,000 and
multiple-row, multiple-feature transplanters cost over
$7,000. Used units are available for less. Most farmers
modify their machines. California distributors of two
major transplanters:
Holland Transplanters Co.
Solex, 220 South Jefferson St.
Dixon, CA 95620
Tel. 916-678-5533
Mechanical Transplanter Co.
Salinas Equipment Co.,
1051-B Tervenae
Salinas, CA 93901
Tel. 800-331-5675 or 800-237-4585.”
(Small Farm News, May/June 1993).
DISEASES OF VEGETABLE TRANSPLANTS
It may still be cold outside, but growers will soon be start-ing
transplants in the greenhouse, if they have not done so
already. Managing diseases is an important aspect of trans-plant
production, but one that is often overlooked until a
problem develops. Diseases that develop during transplant
production can be divided into two general types. There
are diseases such as Botrytis gray mold and Pythium seed-ling
blight that are usually only problems in the greenhouse.
These diseases generally become less important once trans-plants
are placed in the field. There are also diseases that
get started on seedlings in the greenhouse, but cause most
of their damage after plants are set in the field. The patho-gens
that cause this second class of diseases usually survive
on or in the seed and infect as the seeds germinate. This
week I will focus on Botrytis and Pythium. I will cover the
other diseases in the next few issues.
Both Botrytis gray mold and Pythium seedling blight are
common on greenhouse-grown plants. They infect a large
number of plant species, and develop as a result of environ-mental
conditions in the greenhouse. Both of these dis-eases
are favored by conditions that are common in green-houses,
including: high moisture levels, low light levels,
and dense plantings. Once established, these diseases can
be difficult to control. Botrytis causes leaf and stem blights
on greenhouse grown plants. Relative humidity levels above
90% are required for infection, and temperatures between
68 and 76F are ideal for disease development. Short peri-ods
(8 to 12 hours) when the plants are wet are also re-quired
for spore germination and infection to occur. Such
conditions often develop in the late afternoon and evening
as the air within the greenhouse begins to cool. As the air
cools, relative humidity levels increase and water condenses
on plant surfaces.
Adjustments to heating and ventilation systems can help
keep humidity levels down, and increasing air flow within
the greenhouse, especially at plant level, can reduce the
amount of condensation on plants. To discourage infection
by Botrytis, temperatures should not drop below 70F and
relative humidity should not rise above 90%. Bottom wa-tering
or drip irrigation systems, instead of watering with
an overhead spray, also helps keep the foliage drier and re-duces
problems with Botrytis. Water plants early in the day
so that they will dry quickly. Never water in the late after-noon
or evening. Fungicides that are registered for use in
greenhouses, such as Botran on tomatoes, also may be used
to help control Botrytis blights. Pythium can be introduced
into greenhouse plantings in the irrigation water or in soil
brought in on shoes and tools. It also can be present in
planting mixes. Even though most of these mixes have been
steamed or treated to kill pathogens, they may be recon-taminated
between treatment and use. Pythium causes both
pre- and post-emergence damping-off by attacking the roots
and lower stems of seedlings. The development of Pythium
seedling blight is favored by overly wet soils and high hu-midity
levels.
continues, page 3
DISEASES OF VEGETABLE TRANSPLANTS,
continued from page 2
Pythium produces swimming spores (called zoospores) that
can easily move in films of water and can spread quickly
from plant to plant during periods of irrigation. If Pythium
problems develop, remove affected plants and isolate neigh-boring
plants. Attempt to determine and eliminate the source
of contamination. Make sure that irrigation water is “clean”.
If it is coming from an irrigation pond, or some other source
that is exposed to contamination, the water should be filtered
and possibly treated before use. Well water and city water
should be free of Pythium. Manage irrigation water care-fully.
Do not let soils get too dry, or stay overly wet for
extended periods of time. Consider treating the planting mix
or switching to a different brand if another source of con-tamination
cannot be identified. Use fungicide-treated seed.
Most commercially produced seed is treated with captan and
thiram, which are broad spectrum fungicides that will pro-vide
some control of Pythium.
Ridomil 2E (metalaxyl) is effective for controlling Pythium
on many vegetable crops in the field. However, this product
is not registered for use in the greenhouse and thus may not
be used to control Pythium on vegetable transplants. An-other
formulation of metalaxyl, Subdue, may be used as a
soil drench on certain vegetables including tomatoes and
cucurbits. Simple sanitation practices eliminate some sources
of inoculum and help control seedling diseases in the green-house.
Floors, benches, walls, and equipment should be dis-infected
with a 10% bleach solution or other disinfectant.
Remove any plant debris and weeds which may serve as a
source of disease inoculum. Transplant trays should be dipped
or soaked in a disinfectant solution and rinsed before use.
Limit access to the greenhouse to essential personnel only,
and institute procedures to minimize the amount of soil and
other possible contaminants on shoes, clothing, or tools.
(Darin Eastburn) Darin Eastburn, ILLINOIS FRUIT AND
VEGETABLE NEWS VOL. 2, NO. 1, FEBRUARY 21, 1996
PART 2: CRUCIFERS.
There are several diseases of cruciferous crops that are either seed-born
or attack the plant primarily in the seedling stage. The most
common of these is black rot. Black rot is caused by a bacterium that
can overwinter on and in seed or on infested plant debris in the field.
Once this bacterium is introduced into a seed-bed or greenhouse trans-plant
operation, crowded plant densities and high humidity levels fa-vor
its rapid spread to neighboring plants. Wetness on leaves or other
plant parts is required for infection, and the disease develops most
rapidly at temperatures from 80 to 86 F. The margins of infected
cotyledons turn black, and eventually the cotyledons shrivel and drop
off. Small, yellow, v-shaped lesions are the initial symptoms on the
margins of true leaves. These lesions continue to expand and the
affected tissues turn brown. Crop rotation and the use of disease free
seed are the most effective ways to control this disease. A hot-water-soak
seed treatment can eliminate both internal and external bacterial
contamination. Cabbage and Brussels sprouts should be soaked for
25 minutes at 122 F, while cauliflower and broccoli should be soaked
for 20 minutes at the same temperature
Chemical treatments, such as a soak in dilute sodium chloride, are
effective only for eliminating bacteria on the outside of the seed.
Blackleg is another disease that can be carried on and in seed. This
disease is caused by a fungus, and infection of the cotyledons usu-ally
results in plant death. Circular, light brown lesions develop
on true leaves, and circular to elongated form on stems of infected
plants. As with black rot, the most effective means for controlling
blackleg are a combination of disease free seed and crop rotation.
Fortunately, the seed production industry has done a good job of
producing clean seed and treating seeds with fungicides, so that
this disease is not as great a problem as it once was. The fungus
that causes Alternaria leaf spot can also be carried on seed. Infec-tion
can occur shortly after germination, resulting in a small dark
spot on the stem of the seedling. This often leads to damping-off
or stunting of the seedling. Hot-water or fungicide seed treatments
will also help control this disease. For all of the above diseases,
disease development and spread during transplant production in
the greenhouse can be minimized by avoiding high humidity lev-els
and by proper watering techniques that reduce the amount of
time the plants are wet. Wire-stem, or Rhizoctonia damping-off, is
not a seed-born disease, thus not normally a problem in green-house
transplant production. But it can be a problem in seed-beds
or in the field shortly after transplanting. The disease is favored by
wet soils with temperatures at or above 75 F. Rhizoctonia attacks
the stem of the plant near the soil line. The infected tissue shrivels
and turns dark brown. Infected plants may die or be moderately to
severely stunted. Neither seed treatment nor crop rotation is effec-tive
for controlling wirestem. Seed beds can be fumigated to elimi-nate
the pathogen. After planting, a mixture of 4 oz. of PCNB
(75WP) and 4 oz. of Captan (50 WP) in 50 gal. of water can be
used to drench 1000 sq ft. of soil. (Darin Eastburn) [Darin M.
Eastburn, Illinois Fruit and Vegetable News, Vol. 2, No. 2, March
8, 1996]
DISEASES OF VEGETABLE TRANSPLANTS,
PART 3, TOMATOES AND PEPPERS
Some of the most important diseases of tomatoes and pep-pers
are seed-born and brought into the field on infected
transplants. These include bacterial canker and bacterial
speck of tomato, and bacterial spot, which affects both to-mato
and pepper. As the names indicate, these three dis-eases
are caused by bacteria, and the pathogens survive both
on and under the seed coat. Bacterial canker has been an
infrequent but serious disease of tomatoes in Illinois. Un-like
bacterial spot and speck, bacterial canker is a systemic
disease that disrupts the vascular system, causing stunting
and wilting of the plant. This disease can be difficult to
detect in seedlings because it can take 30 days or more from
the time of infection to the first expression of symptoms.
Infected transplants can look perfectly healthy at the time
of planting, but start showing symptoms a few weeks after
they have been set in the field. The disease is especially
severe on transplants that have been clipped or pruned, as
the wounds created during this process provide an easy way
for the pathogen to enter the vascular system of the plant.
continues, page 4
DISEASES OF VEGETABLE TRANSPLANTS, PART 3,
TOMATOES AND PEPPERS
continued from page 3
The symptoms of bacterial spot and speck on leaves of tomato seed-lings
are similar, and appear as small, dark brown to black specks or
lesions which may or may not be surrounded by a yellow halo. Bacte-rial
spot is also one of the most important diseases on peppers in Illi-nois.
If it is established early and weather conditions are favorable,
yield reductions can be dramatic. Initial symptoms on leaves of seed-lings
are similar to those on tomato, but usually lighter brown in color.
All of these bacterial diseases are readily spread by splashing water
and through handling (or clipping in the case of tomatoes). One way
to reduce the spread of these diseases during transplant production is
to repeatedly clean hands and tools between flats or trays when work-ing
with the seedlings. Also, make sure that used transplant trays are
thoroughly washed and soaked in dilute bleach or another disinfectant
before they are used again. Seed treatments also reduce problems with
these bacterial disease. Many seed companies treat tomato and pepper
seeds with chlorine or acid based chemicals. Such treatments do a
good job of eliminating any contamination on the outside of the seed.
However, these treatments do not eliminate any bacteria that are under
the seed coat. Hot water seed treatment is more difficult to do, but it
eliminates both internal and external contamination. Soaking seeds in
water at 122 F for 25 minutes will usually be sufficient for these patho-gens.
For bacterial canker on tomato it may be necessary to go to 132
F for 30 minutes.
Because seed contamination may be associated with a particular vari-ety
or seed lot, it is a good idea to keep different varieties somewhat
separated while in the greenhouse. Monitor the seedlings closely, and
remove or isolate any flats or trays containing seedlings showing symp-toms
of bacterial infection. If purchasing planting stock, buy certified
disease free seedlings from a reputable supplier.
Remember, you rarely come out ahead by purchasing bargain priced
transplants. Also, inspect them carefully prior to planting, and remove
any trays or flats that contain seedlings with symptoms of disease.
(Darin Eastburn) [Darin Eastburn, Illinois Fruit and Vegetable News
(Part 2) Vol. 2, No. 4, April 10, 1996]
If you do notice plants with symptoms, try to determine if there
is a pattern to the problem. For instance, are the affected plants
scattered randomly among apparently healthy plants, or are
there groups of affected plants? Try to determine if the prob-lem
appears to be spreading. Are there severely affected plants
in the middle and mildly affected plants near the edges of the
group? These patterns of development can help you determine
if the problem is the result of an infectious disease. Diseases
such as gummy stem blight and anthracnose often start on a
few plants, and gradually spread to neighboring plants, form-ing
groups or clusters of affected plants. Isolate trays contain-ing
plants that you suspect may be diseased, and watch the plants
in neighboring trays carefully. Overhead watering, handling
the plants, and warm, humid greenhouse conditions promote
the spread and development of diseases. So take steps to keep
foliage dry an to minimize handling of the plants. Fortunately,
the most common virus diseases of vine crops, including cu-cumber
mosaic (CMV), watermelon mosaic (WMV), and zuc-chini
yellows mosaic (ZYMV), are not thought to be seed-borne,
thus they do not usually show up on seedling in the greenhouse.
Squash mosaic (SqMV) is seed-borne, but instances of this dis-ease
on vine crops in Illinois have been rare. (Darin Eastburn)
[Darin Eastburn, Illinois Fruit and Vegetable News Vol. 2, No.
5. April 24, 1996]
VEGETABLE SEEDLING DISORDERS
- (Rick Latin & Dan Egel) - In previous issues, we have
discussed the difference between infectious/ non-infectious
disorders and greenhouse sanitation. Now we would like to
talk about some of the common seedling problems seen about
this time of year. Damping off-Seedlings may collapse at
the soil line. Often, the stem has a brown color at or just
below the soil line. Damping off may be caused by soil fungi
such as Pythium or Rhizoctonia. Water soaked or shrunken
stem lesions (tan or brown) may be an infectious problem
even though the stems do not collapse. Wilting/yellowing-Root
diseases can result in wilted and yellowed seedlings.
The roots may be brown. These problems may be caused by
the soil fungi mentioned above. Leaf spots-There are many
problems that can result in what we call leaf spots. More
than 90% are non-infectious. If the spots are located only on
the edge of the leaf or between the veins, it is likely that the
spots are non-infectious. Seedlings with infectious leaf spots
will occur in a clustered pattern within the greenhouse. Leaf
yellowing-In most cases, yellowed leaves are not symptom-atic
of infectious problems. If the yellowing occurs only on
the leaf margins and/or between the veins, the disorder is
non-infectious. Stunting-Sometimes growers complain that
their seedlings just are not growing. Often, this can be blamed
on poor growing conditions. For example, seedlings that are
grown too cold and/or too wet may end up stunted.
(Diana Lange, editor, Purdue Univ. Vegetable Crops Hotline
No. 314, May 2, 1996)
DISEASES OF VEGETABLE TRANSPLANTS. Part 4:
Vine Crops.
As with crucifers, tomatoes, and peppers, some of the diseases of
cucurbits that cause problems in the field can start on seedlings in the
greenhouse. Gummy stem blight and anthracnose are probably the
most common field diseases to develop during transplant produc-tion.
Bacterial fruit blotch of watermelon and angular leaf spot can
also get started on seedlings. Symptoms of gummy stem blight, also
called black rot on pumpkins, vary somewhat depending on the host
crop. Small, green, water-soaked spots often appear first on the un-dersides
of cotyledons. These spots can expand to kill the entire
cotyledon, and eventually move to the stem, killing the seedling.
Small black specks (called pycnidia) form in infected tissues, and
are useful in the proper identification of the disease. On seedlings
infected with anthracnose, the cotyledons droop and wilt. Lesions
may also form on the stem near the soil-line. Angular leaf spot and
watermelon fruit blotch also initially appear as dark, water-soaked
lesions on the lower surfaces of the cotyledons. All of these diseases
can be seed-borne, surviving on or under the seed coat. Thus, the use
of disease free seed is important. During transplant production, watch
for wilting or dying seedlings and spots or lesions on leaves and stems.
TRANSPLANT DISEASES
-(Dan Egel)- In greenhouses around Indiana vegetable seeds are
being sown, transplants are beginning to emerge and growers are
beginning to worry about plant diseases. Diseases may be infec-tious
or non-infectious. Infectious diseases are caused by fungi
or bacteria that may be introduced on seed. Such diseases in-clude
watermelon fruit blotch, anthracnose of muskmelon, bacte-rial
spot of tomatoes and black rot of cabbage. Other infectious
diseases are caused by fungi that survive in the soil. These dis-eases
include rhizoctonia and pythium damping-off diseases which
affect a wide variety of plants. Infectious diseases can be elimi-nated
or their spread limited by proper greenhouse sanitation.
Non-infectious diseases are sometimes known as the “too
much” diseases. They may be caused by too much or too little
water, sunlight, fertilizer, heat, etc. It is important to note that
while the bacterium that causes watermelon fruit blotch may
spread from one plant to many, a single transplant with fertilizer
burn will not affect any of the plants around it. If a grower recog-nizes
an infectious problem, it is best to remove the transplants
involved as soon as possible. In addition, healthy trays of trans-plants
next to diseased trays may be contaminated and should
also be removed.
Infectious diseases usually start on one plant and spread to
nearby plants. Therefore, infectious diseases often occur in clumps
of plants with similar symptoms. In contrast, brown spots that
occur on every plant in the greenhouse are more likely fertilizer
burn than an infectious disease. Similarly, stunted or yellow plants
that occur near a heater or along a walk way are probably NOT
due to an infectious disease. Problems that start as transplants
can end up as problems in the field. Pay close attention to trans-plant
health. (Diana Lange, editor, Purdue Univ. VEGETABLE
CROPS HOTLINE, ISSUE 312, APRIL 4, 1996)
TREATING TRANSPLANTS RIGHT
- (Liz Maynard) -With the transplant season well underway for
cole crops and beginning for the warm season crops in the south-ern
part of the state, here are some reminders on how to “do the
right thing” for your transplants. Getting them off to a good start
in the field will pay off down the road.
• Harden the seedlings before transplanting. Reduce water and
fertilizer applications, and lower temperature by 5 to 10 degrees
(but not below 50-55 for warm season crops). If possible, increase
light levels by moving them outside. Hardened seedlings will with-stand
the shock of transplanting better. The object of hardening is
to slow growth (not stop it entirely) and promote storage of carbo-hydrates.
• Set transplanting equipment to plant at the proper depth and cover
root ball well.
• Water transplants in after setting. If you use a starter fertilizer
make sure it is well-dissolved and evenly mixed in the tank.
• If your transplants did not grow as well as you would have liked
this year, try to find out why now. Transplant growing media and
irrigation water can be analyzed for pH and nutrients by the Green-house
Media Analysis Lab at Purdue University. The Plant and
Pest Diagnostic Lab can help diagnose transplant diseases. Tem-perature
gradients in the greenhouse can be identified by using a
thermometer at several locations throughout the house. (Diana
Lange, editor, Purdue Univ. Vegetable Crops Hotline No. 314, May
2, 1996)
TOMATO TRANSPLANT DISEASES
- (Rick Latin) - The general health and vigor of our pepper and
tomato transplant crops appear to be very good, despite the
lack of sunshine and preponderance of cool, dark, wet days.
There are, however, a few problems out there that growers
should be aware of. For the first time in many years, we iso-lated
the bacterial speck pathogen from tomato transplants
raised in an Indiana production facility. As you may recall,
we’ve had problems with bacterial spot and bacterial canker in
the past. Symptoms of bacterial speck are nearly identical to
those of bacterial spot on young seedlings. You should be
alerted if you observe a cluster or clusters of small (1/16" di-ameter),
round, dark brown-black spots on true leaves. The
cluster pattern of distribution is an important sign of an infec-tious
problem. The spots will appear on otherwise healthy
leaflets, and are often surrounded by a yellow halo. Unlike
noninfectious spots on seedlings, bacterial speck symptoms
will not occur only between the veins and also will occur on
petioles.
I advise discarding plants with symptoms, and at least all plants
(symptomatic or not) in plastic trays bordering those with spots.
It would be wise to isolate other plants from the same seed lot
and observe them closely for additional outbreaks. Treatment
with copper hydroxide may reduce spread in the field. Also,
the onset of warmer and drier weather conditions will dramati-cally
slow the increase of symptoms in the field. I have also
observed a case of black root rot on tomato seedlings. The
disease is caused by a common soil fungus that takes advan-tage
of plants that are stressed due to growth in small-celled
trays during unfavorable weather periods. The seedlings will
appear somewhat stunted, and show uneven growth over a
single tray or within a given area. Removal of the seedling
from its cell will reveal a layer of darkened roots near the top
of the cell. This disease can be outgrown by the plant if it is
placed in more favorable conditions. The general rule of thumb
is that if the plant is not wilted and has a fairly extensive root
system with plenty of white roots at the margins of the cell,
they will survive and produce in the field. (Diana Lange, Purdue
Univ. VEGETABLE CROPS HOTLINE, ISSUE 315, MAY
16, 1996)
The University of Hawaii at Manoa, College of
Tropical Agriculture and Human Resources, Coop-erative
Extension Service is an Equal Opportunity/
Affirmative Action Institution providing programs
and services to the people of Hawaii without regard
to race, sex, age, religion, color, national origin, an-cestry,
disability, marital status, arrest and court
record, sexual orientation, or veteran status.
DAMPING-OFF OF COLE CROPS
The cool, wet conditions of the past few weeks have been very
favorable for pathogens that attack seedlings of cabbage and other
crucifers. The soilborne fungi Rhizoctonia solani and several spe-cies
of Pythium are the most common causes of damping-off in
crucifers. These fungi usually attack the lower stem just below the
soil-line. The infected tissue becomes dark and shrivels, resulting
in a condition called wirestem. Plants with wirestem can remain
alive, although stunted, for some time, but eventually the plants
fall over and die. Plants that have reached the 3 to 4 leaf stage are
much less susceptible to damping off. Infection by Pythium is fa-vored
by low soil temperatures, whereas Rhizoctonia usually pre-fers
warmer conditions. Damping-off is usually most severe in
fields with high levels of green organic matter, poor drainage, or
soil compaction problems. The best way to avoid damping-off is
to plant in a warm, well drained planting bed. (Darin M. Eastburn,
ILLINOIS FRUIT AND VEGETABLE NEWS, Vol. 1, No. 5, May
17, 1995).
Rain and Plant Disease
- (Dan Egel & Rick Latin) - The microorganisms such as fungi and
bacteria that cause plant diseases usually need water to cause and
spread disease. So the down pour of rain that has occurred recently
in Northern Indiana is bound to result in more plant disease.
Phytophthora diseases in particular may become more severe. Since
we had such a wet spring, Phytophthora diseases may have already
gotten a good start. In addition, some plants remained under water
for several hours. Such conditions may weaken the roots as well as
other plant parts. When plants become weakened, they more easily
become diseased. Phytophthora blight usually first appears in low
areas of the field. If the disease is diagnosed when there are only a
few clusters of plants, fungicide sprays may help. Plants already in-fected
with Phytophthora can not be cured. Symptoms on pepper
plants can be varied. Growers may notice a general wilt, dark brown-black
lesions that girdle roots, stems and branches, rapidly expand-ing
brown-tan spots on leaves, and a rapid rot of affected fruit. The
Phytophthora fungus also affects winter squash and pumpkin. Tur-ban
and acorn squash appear to be the most severely affected.
To control Phytophthora diseases, many vegetable crops are la-beled
to permit the application of chemicals such as Ridomil 2E at
planting. A few vegetables, such as pepper and tomato, may be sprayed
twice after emergence. For tomatoes, a second post planting applica-tion
may be made up to 4 weeks before harvest. Peppers may be
sprayed up to until 7 days before harvest. Read the labels for impor-tant
information about applying these chemicals. Ridomil, however,
will not control the disease on above ground parts. Remember, the
purpose of chemicals such as Ridomil is to prevent additional plants
from being infected.
Fields that are severely affected by Phytophthora this year should
be rotated out of susceptible crops for at least 3-4 years. Using raised
beds with peppers also may provide some relief. Some pepper vari-eties
may have partial resistance.
Avoid tank mixes of “try this one too”. Frantic application of
chemicals at this point is not going to help. Pay special attention to
post harvest intervals.
(Diana Lange, editor, Purdue Univ. VEG CROPS HOTLINE, ISSUE
320, JULY 25, 1996)
SEEDLING DISEASES OF VEGETABLE CROPS
Soilborne fungi belonging to the genera Pythium, Fusarium, and
Rhizoctonia are responsible for many of the seedling disease
problems of vegetable crops. These diseases are usually most
severe under conditions that slow the growth of the young plants,
such as cool soil temperatures, overly wet soils, or poor seed
quality. The control of seedling diseases involves three areas:
the seed, the site of planting, and the environment. Always use
high quality seed that will germinate and establish quickly. If
possible buy seeds or transplants that are certified as disease
free. Many commercially produced seeds are treated with broad
spectrum fungicides, such as captan or thiram, that will help
protect the seeds and young seedlings from seed and soilborne
fungi for a week or two after planting. Choose a planting site
that is well drained and does not have a history of seeding dis-ease
problems. Plant at a time when soil temperature and mois-ture
conditions favor rapid germination and growth. The use of
raised beds can help improve soil drainage and increase soil
temperatures. Fungicides, applied at the time of planting or
transplanting, are registered for controlling seedling diseases
on some crops such as snap beans and peppers. (Darin M.
Eastburn, Illinois Fruit and Vegetable News, Vol. 1, No. 4, May
3, 1995).
SNAP BEANS: Seedling diseases can severely reduce stands
of snap beans. Infection by Pythium, Fusarium, and Rhizocto-nia
can cause both pre- emergence and post-emergence damp-ing
off. Control options include avoiding sites with a history of
disease problems; planting in warm, well drained soil, and the
use of seed treatment or soil applied fungicides. Most commer-cially
produced snap bean seed comes already treated with cap-tan
and/or thiram, both of which are broad-spectrum protectant
fungicides. Apron, a seed treatment form of metalaxyl, can also
be applied to help control infection by Pythium. Ridomil 2E
also contains metalaxyl, and is applied to the soil at or before
the time of planting. PCNB (sold as Terraclor) can be used to
help control Rhizoctonia. Ridomil PC11G contains both
metalaxyl and PCNB, and thus will be useful for controlling
both Pythium and Rhizoctonia. None of the fungicides men-tioned
here are particularly effective for controlling seedling
diseases caused by Fusarium. (Darin M. Eastburn, Illinois Fruit
and Vegetable News, Vol. 1, No. 4, May 3, 1995)
SWEET CORN: The fungi Fusarium moniliforme, Penicil-lium
oxalicum, and several species of Pythium are the most
common causes of damping-off and seedling blights of sweet
corn. Both Fusarium and Penicillium can survive on infected
kernels or in the soil, while Pythium is strictly soilborne. Seed-ling
diseases can be especially serious on shrunken-2 sweet corn
hybrids. The production of shrunken-2, or super sweet, sweet
corn is hampered by poor emergence, irregular stands, reduced
vigor of seedlings, and a high incidence of seedling wilt, when
compared to the standard sugary hybrids. One of the reasons
for this is that most of the shrunken-2 hybrids were originally
developed from lines that were fairly susceptible to some of
these pathogens.
continues, page 7
SEEDLING DISEASES OF VEGETABLE CROPS,
continued from page 6
Resistant breeding lines are available, and the development of
resistant hybrids will help control this problem in the future.
Some seed companies treat their seed with several different fun-gicides
to try to eliminate any external seed contamination, and
to help protect the seed against soilborne pathogens. At this
point the most effective means of managing the problem are
those practices which promote rapid germination and emergence
of seedlings. Proper preparation of the seed beds and place-ment
of the seed are very important, and techniques like seed
priming may help increase germination rates. Those growing
shrunken-2 hybrids for the early market may be forced to plant
when soil temperatures are too cool, but delaying planting until
temperatures are more favorable will help reduce these seed-ling
disease problems. (Darin Eastburn)
Darin M. Eastburn, Illinois Fruit and Vegetable News, Vol. 1,
No. 4, May 3, 1995
GERMINATION AND CARE OF OUR SEEDLINGS
Greenhouse Coverings, Alberta Agriculture, Food and Rural De-velopment
M. Mirza and M. Younus, CDC, North Edmonton.
It is important to get the maximum germination from the seeds.
This can be tough especially when trying to germinate seeds when
it is very cold. Here are some reminders:
**Temperature - Seeds require proper temperatures for germina-tion.
These temperatures are generally higher than what germi-nated
seeds require. The growing medium temperature for toma-toes
and peppers is around 75 degrees F and cucumbers, 81 de-grees
F. Lower temperatures delay seedling emergence, higher
temperatures will inhibit germination or result in a higher per-centage
of off-types. Many growers who do not have bottom
heat and use over-head heated air to maintain the temperature,
may find it difficult to maintain adequate temperature in the ger-mination
area. Focus on temperature in the growing medium us-ing
a thermometer to check. Rockwool and peat moss growing
mediums can show a lower temperature due to evaporative cool-ing
from the surface of the plugs or cubes or pots.
**Moisture - Saturate the rockwool cubes well with pH adjusted
water before putting the seeds in cavities. When using bedding
plant trays, thoroughly soak them before seeding. It is important
to maintain dequate moisture in the germinating media. Remem-ber
the seed has to imbibe water to become turgid. If there is not
enough free water available, the seed looses turgidity and emer-gence
is inhibited. If media is too wet, gas exchange will be a
problem.
**Oxygen - A good germination medium has the inherent capa-bility
of absorbing water up to its water-holding capacity. What-ever
water is held by the growing media is available to the seed.
After thorough watering, the air in the growing medium is ex-pelled
and the medium is considered to be saturated. After a few
hours, based upon the quality of the growing media the water is
replaced by air and thi helps the germination process. If the
media is too compacted or was designed to hold water for a longer
period of time then lower oxygen levels can result and affect ger-mination
rates.
**Relative Humidity - Relative humidity is very important for
seed germination and is one of the most neglected factors where
forced air furnaces are used to 6 heat the germination area. Erect-ing
a plastic tent over the germination bench helps to maintain
close to 100 percent relative humidity. Using intermittent mist
also helps to achieve higher relative humidity.
When using a germination chamber, remove trays from the cham-ber
when 60 to 75 percent emergence has occurred. The timing
is very critical, done too early and the late emerging seeds are
further delayed and if done too late, the seedlings that have al-ready
emerged become stretched and leggy due to the higher
temperature required for germination.
**Early Care - Proper care of the young seedlings is essential to
grow good quality plants. Quality plants are the foundation of a
productive crop which will last for several months. The focus is
on growing a healthy and strong seedling. After germination
the temperature is dropped several degrees below the germina-tion
tempera ure so the plants can be hardened off to better handle
stress.
A complete fertilizer feed has to start early, especially when
growing i an inert media like rockwool. Vegetable seedling grow-ers
are familiar with the use of higher electrical conductivities
(E.C.) to slow down the growth of plants, especially tomatoes.
The goal is to avoid the stretching of the plants. Stretched or
leggy plants become weaker and unbalanced in relation to veg-etative
and reproductive growth. Growers can use potassium
sulfate or sodium chloride (most commonly used in tomato seed-ling
management) to raise the E.C. of the standard fertilizer so-lution.
The E.C. of seedless cucumbers can be raised as high as
4.0 millimhos, while tomatoes can tolerate an E.C. of up to 7
millimhos until the first cluster of flowers are set. Calcium
nutrition is important. Most fertilizers with N, P, and K do not
contain calcium and generally not enough calcium is available
in the water. Greenhouse grade calcium nitrate contains about
19 percent calcium, while ready-made 15-0-15 contains about
12 percent calcium. Liquid calcium nitrate may contain even
less calcium, 11 percent in one formulation. It is important to
know the source of the fertilizer and the amounts of nutritional
elements they contain. Spacing is vital! When growing bigger
plants, make sure they don’t get crowded since crowding re-sults
in weak and stretched plants. Often these plants do not
recover.
(Michael D. Orzolek, Peter A. Ferretti, Penn St. Horticulture
Vegetable Newsletter, Vol. 8, No. 12, December 1996)
Words of Caution: Note that most articles provided here
were written for growers in northern climates. Thus, not all the
information is directly applicable to Hawaii. Also pesticides and
chemicals used in other states may and are often not registered for
use in Hawaii i.e. read the label prior to using any pesticide/chemical
on your crop/farm. For specific questions and clarifications con-tact
your county extension agent or the UHM Plant Pathologist
Specialist.
1996 - VEGETABLE CULTURE AND MANAGEMENT IN
A WET YEAR
M. Orzolek
Precipitation in 1996 has been above normal to say the least and
has caused a few problems with vegetable producers in Penn-sylvania.
Certainly, scheduling vegetable plantings and harvest
has been very difficult with potential for different planting dates
to be harvested on the same day this year. If July temperatures
are in the mid-eighty to ninety degree range for several weeks,
growth and development on young crops will increase dramati-cally
and change to reproductive growth rather quickly.
Excess moisture has also caused problems with pests, especially
weeds. Moist soils this late in the year encourage weed seed
germination and growth while at the same time dilute the amount
of herbicide applied in the field to control weeds. Consequently,
growers should check their fields for additional weed pests de-veloping
in their fields and take appropriate steps to eradicate
the weeds either with herbicides or other efficient methods. In
addition to weeds, leaf blights are starting to infect plants be-cause
of the wet weather, and fields should be closely moni-tored
for foliar diseases in the next couple of weeks.
The other problem growers may be noticing in their fields is the
yellowing, purpling, or interveinal chlorosis of crop plant tis-sue.
With so much rain in the last 6 weeks, leaching of nitrates
from soils has been a concern. Addition of modest amounts of
fertilizer (20 to 40 lbs/A of actual N) may help ensure maxi-mum
yields at harvest time. Potassium levels may be low be-cause
potassium is moderately water soluble and would have
been leached this last 6 weeks with above normal rainfall in
most counties of the state. (Michael D. Orzolek, Peter A. Ferretti,
Penn State Horticulture Vegetable Newsletter, Vol. 8, No. 7,
July 1996)
EFFECT OF TRANSPLANT TRAY TYPE AND TOMATO
CULTIVAR ON THE INCIDENCE OF FUSARIUM CROWN
AND ROOT ROT IN TOMATO TRANSPLANTS
by R. S. McGovern and C. S. Vavrina, UF-SWRES, Immokalee,
Florida.
The effect of transplant tray type and tomato cultivar on the
incidence of Fusarium crown and root rot caused by the fungus
Fusarium oxysporum F. sp. radicis-lycopersici (FORL) was ex-amined
in a commercial transplant house. Four common south
Florida tomato cultivars, Agriset-761, PAP-34283, Sunbeam, and
Sunny, were seeded in a peat-based medium in five different trans-plant
trays, two polystyrene and three Styrofoam trays with re-spective
cell volumes of 19 and 28 cm3, and 6, 20, and 32 cm3.
Six weeks after seeding, the roots and crowns of eight randomly
selected transplants from each tray type were surface disinfected
and plated on Komada’s selective medium for Fusarium
oxysporum. Following removal of all transplants and surface
disinfestation, cotton tipped applicators dipped in sterile water
were used to swab ten cells of each tray and to streak plants of
Komada’s. Isolation of FORL was assessed 5 days following
incubation of plates at 28 C/82 F. No significant differences in
varietal susceptibility to FORL were detected. Crown rot inci-dence
was significantly highest in transplants from Styrofoam
trays with the largest cell sizes (20 and 32 cm3), and FORL was
most frequently recovered from Styrofoam trays. Steam disin-festation
of Styrofoam at 71 C/160 F for 45 min eliminated FORL.
(Michael D. Orzolek, ed. PENN ST HORTICULTURE VEG-ETABLE
NEWSLETTER, Vol. 6, No. 2, 1994)
Diseases That Affect Vegetables After Transplanting
For the following vegetable diseases which appear after trans-planting,
control programs should be initiated by the seedling
producer:
Asparagus: Rust.
Crucifers: Blackrot, black-leg, clubroot, Fusarium yellows, and
downy mildew.
Eggplant: Fruit rot, and Verticillium wilt.
Lettuce: Botrytis gray mold, and mosaic virus.
Melons: Fusarium wilts, powdery mildew, anthracnose, and
mosaic viruses.
Onion: Smut.
Pepper: Bacterial spot, and mosaic viruses.
Tomato: Bacterial spot, speck, and canker; Fusarium and Verti-cillium
wilts; and mosaic viruses.
Control: Controls include use of pathogen-free seed, various
seed treatments, use of disease-resistant varieties, use of patho-gen-
free media, control of weeds that are sources of viruses,
control of insects that transmit viruses, isolation of seedlings
from diseased plants, application of specific bactericides and
fungicides, and minimizing contact with seedlings. Specific
controls are noted by disease for each crop in disease control
tables included below for each crop.
(Dr. Alan A. MacNab, Penn State, VEGETABLE NEWSLET-TER:
DISEASES, March, 1996, Volume 25, Number 3)
Sterilization and Sanitation of Flats
Old flats may be contaminated with fungi capable of causing damp-ing-
off of seedlings when they are grown in such flats; therefore,
steam all flats before re-use. Flats can be stacked on a bench or on
the floor and covered with a tarpaulin beneath which steam is re-leased.
Minimum treatment should be 180 degrees Fahrenheit for 30
minutes. Flats should be separated horizontally by 0.75-inch strips
or stacked in a staggared manner with vertical spaces of about 1-
inch. Treated flats can be used immediately.
If steam is not available, and chemicals must be used, chlorine
solutions (1 part laundry bleach to 9 parts of water) are probably the
most effective sanitizers. Dip the flats; then drain the solution back
into the tank. Stack the flats under a tarpaulin for 24-hours; then
uncover, but keep flats wet by spraying with water until odor is gone
(4 to 6 days). To be sure flats are safe for use, put a wet treated flat
into a plastic bag for 24 hours and then check the closed bag for odor
as soon as the bag is opened. Two kinds of chemical disinfestants are
available:
1) Phenolics: Phenol-type disinfestant such as Amphyl LF-10, ef-fective
at 1 ounce in 2 gal water.
2) Quaternary ammonium salt compounds such as Physan-20, used
at 1 oz in 2 gal of water.
Both the phenolic and quaternary ammonium salt disinfestants are
reactive and break down quickly upon contact with air and organic
matter. Effectiveness is enhanced by precleaning surfaces before
disinfestation. As with most chemicals, disinfestants should be made
up and used promptly.
Precaution: Use rubber gloves when dipping, do not use formal-dehyde
or chlorine in a house with living plants, and be sure flats are
kept wet until all odor is gone. (Dr. Alan A. MacNab, Penn State,
VEGETABLE NEWSLETTER: DISEASES, March, 1996, Volume
25, Number 3)
Phomopsis Blight of Eggplant
Phomopsis blight caused significant losses to some eggplant fields on
Oahu. Phomopsis blight is caused by the fungal organism Phomopsis
vexans (Sacc. and Syd.) Harter. This disease ranks second only to bac-terial
wilt in destructiveness to eggplant in the tropics. Phomopsis blight
affects the main stems, branches, fruit, and leaves of eggplant. Only
eggplant is affected by this disease. Other names that describe the symp-toms
expressed in eggplant include: damping off, seedling stem blight,
collar rot, canker, leaf spot, leaf blight, stem blight, eggplant blight, tip-over,
fall-over, and fruit rot. This disease was reported in Hawaii by
F.L. Stevens in 1925.
Symptoms: Fruit: Affected fruit have pale, sunken spots. The spots may
expand and affect the whole fruit. The spots usually start at the calyx
and then expand into the fruit. The fruit rot is soft and causes a light
brown discoloration of the flesh. In dry conditions, the fruit shrivel and
dry up into black mummies. The fruit rot may go undetected at packing
and show up as a postharvest rot. The presence of pycnidia, especially
evident in fruits, helps with field diagnosis. These pycnidia appear in
large numbers and resemble tiny black pimples just under the fruit sur-face.
Often they are arranged in concentric circles (arranged like the
rings in a bull’s eye target).
Stems: Cankers appear on the main stems and branches. Cankers com-monly
occur at the base of stems and appear as a constriction or girdled
area. The bark may slough off and the inner wood may be exposed.
Affected plants may wilt rapidly in the field. Plants with girdled stems
may be prone to lodging in high winds.
Seedlings: Phomopsis blight can spread very rapidly in fields when seed-lings
become infected and are later transplanted. The seedlings may
show the stem canker (girdling) symptom which can be easily confused
with other common damping off organisms.
Other diseases in Hawaii such as verticillium wilt and bacterial wilt
also cause wilting in eggplant. Growers should learn to diagnose these
important eggplant diseases. Laboratory analyses (such as the D1 analysis
available through the CTAHR Agricultural Diagnostic Service Center)
can be used to confirm field diagnoses by growers. Pycnidia an
dpycnospore production are promoted by growth of the fungus on 4 to
7% oatmeal agar, at 68 to 89F and in light.
Disease cycle. The fungus can live within seeds or as spores
on seeds and in soil and crop residue. The fungus remains alive for
more than one year in fields after eggplant has been grown and cleared
away, but completely dies out by the third year. Fungal conidia are spread
through splashing rain, insects and tools. Wet weather and high tem-peratures
promote disease development.
Phomopsis blight management. It is important that growers start
with clean seed which will appear bright and plump. Seed
batches which have dark or shriveled seeds are suspect. Seeds
can be treated for 30 minutes in water at 122F (see accompany-ing
article on seed treatments). Seed beds or nurseries should
be kept free of disease or entire fields can become contami-nated
through infected transplants. Avoid wet conditions in the
seed bed or nursery which can promote the spread of the dis-ease.
To help keep fields free of inocolum, follow a 3-year or
longer rotation. Diseased plants should be plowed under and
affected fruit should be picked quickly and disposed of prop-erly.
Resistance is available in some foreign varieties and re-lated
species. Varieties grown locally are apparently suscep-tible
(Randy Hamasaki, Univ. Hawaii Oahu Vegetable Grow-ers’
Newsletter, Vol. 6 No. 1, March 1994).
Seed Treatments
Starting off with clean seed is a basic and sound step in crop
production which is often overlooked by growers. Seed treat-ments
can help prevent early infection by seedborne diseases
and help reduce risk of a poor crop stand or crop failure. You
have probably ready many articles about improvements in seed
treatment technology being offered by commercial seed pro-ducers.
Seed treatment can be broadly grouped into two cat-egories:
1) eradication treatments which kill disease causing
agents on or within the seed and 2) protective treatments which
are applied to the surface of the seed to protect against decay,
damping-off, and soil insects. Seeds of beans, cucumbers, and
sweet corn, when planted in unfavorable soil conditions (cold
and wet soils), should be treated with thiram or captan. The hot
water seed treatment is the major means of eradication. Veg-etable
growers should become familiar with the advantages,
limitations and procedures of seed treatments.
When using hot-water seed treatment, it is important to pre-cisely
follow the temperature and time directions. Use a good
thermomoter and a hot water system which provides uniform
temperature (no hot or cold spots). Shown below are guide-lines
for the hot-water treatment of some crop seeds:
Hot water Seed treatments
Crop Temperature (F) Time (minutes) Seedborne diseaseas controlled
Broccoli 122F 20 minutes Alternaria, blackleg, black rot
Cabbage 122 25 Alternaria, blackleg, black rot
Eggplant 122 30 Phomopsis blight, anthracnose, rhizoctonia
Pepper 122 25 Bacterial spot, Rhizoctonia
Tomato 122 25 Bacterial canker, spot, and speck, anthracnose
Reference: Lorenz and Maynard. 1988. Knott’s Handbook for Vegetable Growers, 3rd Ed.
(Randy Hamasaki, Univ. Hawaii Oahu Vegetable Growers’ Newsletter, Vol. 6 No. 1, March 1994).
9
Phomopsis on Eggplant

Diseases of vegetables transmitted by in-fected
transplants
Crop Symptoms Cause
Broccoli, Yellow “V” shaped lesion Black Rot
Cabbage, at margin of leaf (bacterium)
Cauliflower Small galls or swellings Root Knot
on roots (Nematode)
Eggplant Yellow foliage frequently Yellows
with ringspot (virus)
Onions Roots are pink and Pink Root
shriveled (fungus)
Pepper Plants die rapidly, stems (Phytoph-are
dark and often woody thora Root
rot (fungus)
Angular leaf spots on Bacterial
margin and tips of leaves Leaf Spot
have ragged appearance (bacterium)
Leaves are distorted and Virus
may have a mosaic ap- (several
pearance, plants are viruses).
sometimes stunted
Irish Rough, scabby lesions on Scab (bac-Potatoes
tubers terium)
(seed pieces) Brown ring just inside of Ring Rot
peeling (bacterium)
Small raised areas on Root knot
surface of potato (nematode)
Tomato Woody dark stems, plants Collar Rot
wilt and die (fungus)
Foliage has small angular Bacterial
shaded spots Leafspot
(bacterium)
Leaves are distorted and Virus
may have a mosaic pattern, Leafspot
leaves sometimes curl (Viruses)
downward and develop a
purple color. Leaves may
develop necrotic ringspots
Roots have small swellings Root knot
or galls (nematodes)
(J.D. Johnson and G. Philley, Disease Management. In: Vegetable Growers’
Handbook, 2nd ed. Texas Ag. Extension Service).
10
Rhizoctonia Seedling Blight
Rhizoctonia, a soil inhabiting fungus affects a number of
vegetables including beans, cabbage, carrot, celery, cow-pea,
cucumber, lettuce, okra, peas, pepper, potato, soy-bean,
strawberry, and tomato. The following information
comes from Dr. Tom Kucharek’s Univ. of Florida exten-sion
publication on this disease: “Rhizoctonia is capable
of causing plant diseases over a broad range of soil tem-peratures,
soil pH, soil types, fertilizer levels, and soil
moistures. The versatile nature of Rhizoctonia results from
its broad genetic potential. Individual isolates of Rhizoc-tonia
can cause plant disease on numerous plant species
and under varied environmental conditions... For practi-cal
reasons, Rhizoctonia is becoming known as “Rhizoc-tonia
complex” as compared to its old name Rhizoctonia
solani... Even though soil fumigation is highly effective
against Rhizoctonia, recontamination of fumigated areas
should be avoided. Any method that reduces movement
of soil from nonfumigated areas to fumigated areas will
achieve this goal. For example, minimize stepping in fu-migated
areas from nonfumigated areas. Avoid soil wash
due to rain or irrigation from nonfumigated to fumigated
areas.
“The following control measures used collectively will
reduce seedling blights caused by Rhizoctonia and other
fungi. The major objective with this group of control mea-sures
is Rhizoctonia control on seedllings and stems of
young plants by establishing a fast growing seedling which
essentially reduces the “hazzard time” as young tender
plants are more susceptible than older plants.
“1) Use only healthy disease-free seed, seed pieces, or
transplants. Although Rhizoctonia is not notorious for be-ing
seed transmitted, poor quality seed will germinate
slowly, if at all, which offers a distinct advantage to Rhizoc-tonia.
2) Avoid deep seeding, if mositure permits, as deep
planting is advantageous for Rhizoctonia infection. Like-wise,
deep setting of transplants should be avoided. 3)
Especially in fields where fumigation was not used, plant
when the soil temperature is suitable for rapid germina-tion;
4) Seed should be treated with fungicide for protec-tion
against infection from Rhizoctonia in the soil. Seed
treatment fungicides such as captan and thiram are
nonsystemic in the plant, but they are labelled for use on
numerous plant species... 5) Use crop rotation; 6) Prepare
land so that a minimum amount of old plant debris is on
the soil surface; 7) When double cropping, allow green
matter to decompose for 30 days after bottom plowing the
old crop. Undecomposed green matter has been a major
source of Rhizoctonia inocolum on green beans and soy-beans
in Florida; 8) Control soil insects and nematodes.
These organisms weaken the plant, thereby predisposing
the plant to infection; 9) Avoid over seeding and close
transplanting as Rhizoctonia can grow from an infected
plant to adjacent healthy plants; 10) When cultivating,
avoid moving the soil onto stems.” (T. Kucharek, Univ.
Florida Coop. Ext. Serv. Pl. Path. Fact-Sheet, PP-1).

 

11
Dwight Sato, CES Hilo
Tel. 808-959-9155, Fax. 808-959-3101, dwights@hawaii.edu
Randy Hamasaki, CES Oahu
Tel. 808-247-0421, Fax 808-247-1912, rth@hawaii.edu
Alton Arakaki, CES Molokai
Tel. 808-567-6833, Fax. 808-567-6818,
ARAKAKIA@AVAX.CTAHR.HAWAII.EDU
Robin Shimabuku, CES Maui
Tel. 808-244-3242, Fax 808-244-7089,
shimabukur@AVAX.CTAHR.HAWAII.EDU
Hector Valenzuela
Vegetable Crops Assoc. Extension Specialist
Tel. 808-956-7903, Fax. 808-956-3894, hector@hawaii.edu
http://agrss.sherman.hawaii.edu/hort/
VEGETABLE DISEASES TO WATCH FOR
Although weather conditions have varied somewhat over
the state, most areas have had an over-abundance of rain.
(How’s that for understatement?) The wet and warm con-ditions
of the south and the wet and cool conditions of the
north may result in the development of particular disease
problems on vegetable crops. The hard, driving rains that
occurred in many areas not only helped disseminate patho-gens
from plant to plant and soil to plant, they also created
small wounds on leaves and stems that can serve as sites of
infection. In areas receiving heavy rains, growers should
be especially watchful for bacterial diseases. Not only do
bacterial pathogens need splashing rain and films of water
on plant surfaces to spread and infect, many of them can
only enter plants through wounds or other openings in the
plant. The prevalence of bacterial spot on peppers and to-matoes,
bacterial speck on tomatoes, angular leaf spot on
cucurbits, black rot on crucifers, bacterial blights of snap
beans, and other bacterial diseases may increase following
heavy rains. For these diseases it is important to recognize
the problem early and begin applications of copper based
fungicides/bactericides as soon as symptoms appear. Other
diseases to watch for over the next few weeks include early
blight and Septoria leaf spot on tomatoes, especially in the
south. On vine crops watch for the initial symptoms of Al-ternaria
leaf spot, gummy stem blight, and anthracnose.
Phytophthora blight may become a problem on peppers and
vine crops in low areas or where soils remain saturated for
an extended period of time. On sweet corn, symptoms of
northern leaf blight, gray leaf spot, anthracnose, and other
foliar diseases may begin to appear in the near future. Many
of these diseases are particularly damaging to young plants,
so it is important to identify problems early and initiate the
appropriate management strategy. (Darin Eastburn) [Darin
Eastburn, ILLINOIS FRUIT AND VEGETABLE NEWS
Vol. 2, No. 9, May 30, 1996]
COOL WET SOILS AND PROBLEMS WITH DAMP-ING-
OFF, ROOT ROTS, AND SEED DECAY
Much of Illinois has received healthy doses of rain (and more)
over the past few weeks. The combination of wet soils and
the continuing cool temperatures means that conditions are
favorable for some of the pathogens that cause root rots,
damping-off, and seed decay diseases. Root rots and damp-ing-
off caused by species of Fusarium, Pythium, and Rhizoc-tonia
are usually more severe in cool wet soil because the
plants grow slowly and remain in the susceptible seedling
stage for a longer period of time. This gives the pathogens
more time to infect and damage roots and lower stems. Green
beans are particularly susceptible to these seedling and root
rot diseases. Cabbage and other crucifers may develop “wire-stem”
as a result of infection by Rhizoctonia solani at or
just below the soil line.
Dark sunken lesions girdle the stem, leaving the wiry inner tis-sues
of the lower stem. Plants with wire-stem usually do not fall
over, but they do stop growing and develop an unhealthy stunted
appearance. Typical captan / thiram seed treatments will be of
some help in protecting the seed, but they may not be enough
when conditions are extremely favorable for disease develop-ment.
PCNB (Terraclor can be used on green and dry beans and
some direct-seeded crucifers to help control Rhizoctonia root
rots and wirestem. PCNB is available in several formulations
and is applied to the seedbed at the time of planting. It is not
registered for use after seeding or transplanting. Products con-taining
the fungicide metalaxyl will help control damping-off,
root rots, and seed rots caused by Pythium. Metalaxyl (Ridomil)
can be applied as a seed treatment (Apron) on legumes, beets,
carrots, and corn.
Ridomil may also be applied to the soil as a pre-plant incorpo-rated
treatment or to the soil surface after planting on several
vegetable crop species. Ridomil PC 11G contains a combina-tion
of metalaxyl for the control of Pythium and PCNB for the
control of Rhizoctonia on beans. Unfortunately, there are no
fungicides that are very effective for controlling seedling prob-lems
caused by Fusarium. From a diseases prevention stand-point,
it is always best to plant into a warm, well drained soil,
but other factors may require that seeds or transplants be planted
in a less than ideal environment. By being aware of the prob-lems
associated with seedling in cool, wet soils, growers will be
better able to assess the risks and benefits of planting early. (Darin
Eastburn) [Darin Eastburn, Illinois Fruit and Vegetable News
Vol. 2, No. 6, (Part 2), May 8, 1996].

 

 

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