September 1, 1998
Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967 or

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 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 UVM)

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)

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 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, UVM)