REPORTS FROM THE FIELD
Kocide has been very effective on powdery mildew
of cucubits again this year; seems to stop it cold with one or two applications.
Looking for late blight on spuds, but none yet. Today has been drizzle
all day,so may see it soon. Have not sprayed copper for it yet. No rain
to speak of for weeks irrigating heavy for this time of year.(Norwich)
Still many blueberries on the vine, although many have fallen or are soft. Late varieties are ripening earlier than usual, but the large crop volume will still allow us to operate the pick?your?own well into September. Vole population seems all too healthy! (Saxton's River)
What crop? Looks like venison this week. We had the game warden look at the situation and he agreed that there seemed to be no alternative but to shoot the deer. I've been out alot but still have not seen one. The damage continues. Fall zuchini looking very good. Had 2" of rain today, mostly in 15 minutes. Tomatoes just about finished from disease. Saw a cucumber beetle in the greenhouse today. Got a great crop of horn worms in the greenhouse, but the kids are great at finding them. (Charlotte)
We were hit with golf-ball size hail and tremendous high winds that caused total devastation to all our small crops. Even the greenhouse covers have holes and must be replaced. (Bradford)
LATE BLIGHT ON POTATO AND TOMATO
Late blight has afflicted both potato and tomato
on many farms in the State. This is the first year I have seen severe economic
loss in tomato due to late blight in Vermont. The tomato severity I have
seen is directly related to planting tomato adjacent to potato. The late
blight fungus (Phytophthora infestans) does
not overwinter in infected tomato debris as do both early blight and septoria
leaf spot. The late blight organism can only overwinter in live tissue
(potato tubers). All of the infection we are now seeing originated from
infected seed potato or infected potato tubers
that remained in the field from last year. At one time fungicides such
as ridomil nearly eliminated the fungus from seed production. Resistance
to this fungicide by Phytophthora has now resulted in late blight problems
we have not seen in more than 15 years. A severe late blight
epidemic was even found in a greenhouse tomato operation where potato was
planted nearby. I strongly recommend that people do not plant tomato and
potato in close proximity. Also, do not plant field tomato next to tomato
greenhouses. Plant these crops in fields as separate as possible and use
a protective fungicide regularly next year. For this year, maintain the
protective use of fungicide. In situations where a strong protective fungicide
program was not used earlier and severe symptoms are noticed, fungicide
use is futile. (Alan Gotlieb ¶¶Òõ̽̽)
BLACK ROT ON CUCURBIT FRUITS
Black rot is caused by the fungus Didymella bryoniae.
When this pathogen infects other plant parts the disease is called gummy
stem blight. Black rot can be a very serious pre- and postharvest fruit
rot especially in winter squashes and pumpkins. Symptoms for black rot
vary depending on the fruit infected. In winter squash, particularly butternut
squash and sometimes pumpkin, it can appear in the field before harvest.
On butternut squash, symptoms develop when fruit are immature. A superficial,
tan to white petrified area can develop with distinct concentric rings
on the surface of the butternut fruit. Within these rings, signs of the
fungus called pycnidia, are embedded in the fruit tissue. More often, when
fruit is damaged prior to or during storage, a brown to pinkish water?soaked
area develops, which eventually blackens and has conspicuous, protruding,
fungal fruiting bodies.
The most effective control for this disease is to catch it when it is first seen as gummy stem blight in the field. Planning ahead for next season, early control will reduce the number of fruits lost and provide higher quality fruit for transit and storage. Another preventive measure for this disease is a 3?4 year crop rotation with other crops to reduce pathogen survival in diseased vines and crop debris. This disease may be seedborne, so the use of disease?free seed and clean uncontaminated growing trays for seedlings will help reduce infection. At this time, when the disease has already started to develop on the fruit, special care should be exercised to avoid rind injuries to squash and pumpkins, because wounds allow entry for the black rot organism in storage. The fruits will develop a corky protective tissue and heal wounded areas when properly cured. Curing at 20-25°C (68-77°F) or higher for 1-2 weeks will harden the rinds. Butternut, Delicious, and Hubbard squash, as well as pumpkins respond nicely to this treatment. Additional storage can be at 11-16°C (52?60°F), with an optimum at 13°C or 55°F, and with relative humidity between 55-75%, with an optimum of 60%. (Adapted from U. Illinois)
FRUIT ROTS ON PUMPKIN
The time to stop fruit rots was when plants began
to vine and set fruit. Besides black rots, common pumpkin fruit rot problems
include the fruit phases of angular leaf spot and bacterial leaf spot,
Fusarium rot, Phomopsis black rot, and Phytophthora fruit rot. Angular
leaf spot and bacterial leaf spot appear on the fruit as small, (less than
1/8 inch in diameter) water-soaked lesions that become tan to white in
the center. Fusarium rot, black rot, and Phomopsis black rot produce larger
circular lesions on the fruit, while Phytophthora fruit rot starts as a
circular spot, but quickly increases in size to cover large areas of the
fruit. An important disease management strategy includes a 3 to 4 year
crop rotation schedule because the pathogens that cause these diseases
can all overwinter on infested crop debris in the field.
Many of these diseases, such as the leaf spots
and black rot, get started on other parts of the plant, then spread to
the fruit as they develop and mature. Beginning a fungicide/bactericide
spray program when plants start to vine and set fruit will reduce the level
of disease on leaves and stems and help reduce the amount of inoculum available
to infect fruit later in the season. Copper based materials work best on
angular and bacterial leaf spot, and provide some control of fungal diseases.
Chlorothalonil or mancozeb should provide control of black rot (gummy stem
blight) and some control of Phytophthora fruit rot if applied when plants
began to vine. Fungicide applications do not control Fusarium fruit rot
very well. By the time fruit rots appear on pumpkins, the best control
measures can only help limit the spread of the problem. This is difficult
when the fruit are covered by a dense canopy of leaves. Avoiding wounding
injuries during harvest will help reduce the post harvest phases of these
diseases. (Adapted from U. Illinois)
BLACK DOT ON GREENHOUSE TOMATOES
Black dot root rot has been diagnosed on greenhouse
tomatoes in Vermont. This disease, part of the brown root rot complex,
is caused by the fungus Colletotrichum coccodes. If the inoculum is allowed
to build up in crops grown without rotations it can be very destructive.
Symptoms become evident about the time fruits begin to ripen. Brown lesions
appear on roots and these eventually die. Secondary roots may be stunted
and decomposed. Diseased plants are easily pulled up due to the damaged
root systems, and often they wilt during the middle of the day but recover
at night (this can resemble Fusarium wilt). The first blossoms set fruit
but the later ones often drop, leaving the upper half of the vine sterile.
Small feeder roots turn brown and rot away. In the rotted area or along
the small infected roots the tissue can become dotted with black stromata
(fungal structures) just large enough to be seen with the naked eye. From
these stromata comes the fungal spores. These spores germinate readily
but require several weeks to cause new infections in weakened plants.
The fungus lives over winter in old diseased parts
or in the soil humus, especially damp straw. The stromata can survive in
the soil for up to one year. Although some Colletotrichum is always present
in most soils, the level rises rapidly when susceptible plants are grown
successively in the same soils. The level recedes to normal after 1 or
2 years of grasses, cereals and other resistant crops. Infection of this
disease depends of the condition of the plant. If tomatoes are growing
vigorously, there may be no root infection. Poor nutrition, unfavorable
soil conditions, high soluble salts, low soil temperatures and other weakening
conditions are extremely important for the disease to develop. In greenhouse
situations where inoculum levels are high, it may be necessary to change
the soil or sterlize the beds with heat.
(Ann Hazelrigg, ¶¶Òõ̽̽)