SUMMER VEGETABLE PESTS TO WATCH FOR
The following pests are showing up in various Northeast locations. For more info on control measures consult the New England Vegetable Guide (ask me if you need a copy) or view the updated Guide at www.nevegetable.org/ . Pest management guides from several other states are linked to the Vermont vegetable and berry web site (shown above). Click on ‘vegetables’, then scroll down and select a state.
BACTERIAL CANKER ON TOMATO
(adapted from John Mishanec, Cornell Extension)
Bacterial canker is showing up in many fields in the region and in some greenhouse tomatoes in Vermont. First symptoms are dry, dark brown spots along the edges of the leaves. On the fruit symptomatic spots are small, about the size of a pin head, with a white halo. Early blight looks somewhat similar with brownish bronze colored lesions on the leaf but does not cause these spots on fruit. Bacterial canker often spreads through entire plantings in the field if the problem started in greenhouse where transplants are very susceptible to the spread of bacteria since they are grouped and watered close together. Plants may grow fairly well in the field till a heavy fruit load and hot weather create stress, then symptoms appear. Some growers have saved their crop with frequent copper sprays to the point that their plants are practically blue-green. Copper plus mancozeb is recommended for conventional growers while several fixed copper materials can be used by organic growers. Very clean greenhouse conditions, use of hot-water treated seed and rigorous crop rotation are needed to eliminate this problem on your farm.
TWO SPOTTED SPIDER MITES
(adapted from Rutgers Extension)
Two spotted spider mite outbreaks have been reported in several mid-Atlantic states on field and vegetable crops. These pests are generally associated with hot, dry weather. Check eggplant, tomato, cucurbit, bean, and pepper fields at least weekly to spot spider mite problem areas. Concentrate on border areas, or field edges near hedgerows, or vegetable fields bordered by field crops such as soybeans. Look for the early signs of damage: white stippling at the bases of the leaves, whole areas of the field looking off-color, followed by yellowing of the leaves, webbing, and eventually defoliation. If the plants look off-color, look closely on the leaf undersides to determine if mites are the reason (a hand lens will help!). Thorough coverage including leaf undersides is necessary for effective control with miticides; use drop nozzles, or high pressure sprayer. Do not wait until the population is high, leaves curl, turn yellow or brown, or webbing begins to form as control will be reduced or not achieved at all.
WHITE ROT IN ONIONS AND GARLIC
(adapted from Eric Sideman, Maine Organic Farmers and Gardeners Assn.)
White rot is one of the most destructive fungal diseases in the onion family. Symptoms on the leaves include premature yellowing and dying of the older leaves and then death of the plant. White, fluffy fungal growth on the root end of the bulb eventually moves around the bulb and inward between the storage leaves of onion and cloves of garlic. Small, black, pea-like sclerotia form in the decaying tissue. There are no known spores, the fungus reproduces only by the sclerotia, which can lie dormant in the soil for many years until roots of a host plant grow nearby. The fungus can then grow to neighboring plants and spread down rows of onions and garlic, or it can spread in infested soil on equipment or boots or by planting infected sets and transplants. Animals feeding on diseased bulbs can defecate viable sclerotia. Control is by good sanitation. Use clean seed for garlic and clean sets and transplants. Wash off soil from tools, boots, equipment, etc, after working in infected fields. If the infection is low, which is usually the case the first year it is found on a farm, pull the infected plants and destroy them.
BACTERIAL SPOT IN PEPPER
(adapted from Rutgers Extension and Ann Hazelrigg)
Bacterial spot is a problem some Vermont pepper fields. Symptoms on leaves include small, brown water-soaked lesions that turn brown and necrotic in the centers. Spots may coalesce and form large blighted areas on leaves and premature defoliation can occur. On fruit, brown lesions can form which have a roughened, cracked wart-like appearance. High temperatures, high relative humidity and rainfall favor bacterial spot development. Losses can be reduced somewhat by maintaining high levels of fertility, which will stimulate new growth. Manage the disease by rotating out of solanaceous crops (and weeds) for 2 years, use hot water treated seed, and plant resistant varieties. Be sure to disinfest pots, flats, trays, etc. Chemical controls often don't work that well, but choices include basic copper sulfate, or fixed copper alone or with maneb. Do not to use a high pressure air blast sprayer as this can do more harm spreading bacteria than not spraying at all. Work in infected fields last, and destroy crop residue after harvest.
DOWNY AND POWDERY MILDEW IN CUCURBITS
(adapted from UMass and Cornell Extension)
Downy mildew is a very damaging disease moves up from the South but it has not yet been reported in New England or New York this year. Scout cucurbit fields by looking on the undersides as well as tops of the leaves (especially older leaves) for small round spots of white spores. Scout for powdery mildew at the same time. This disease is familiar to most growers since it occurs most every year. Once you see it, that’s the time to initiate control sprays which will also help prevent downy mildew. Once established, it cannot be controlled. Regular scouting will help you find downy mildew early, if it does come in to the region, which is even more important because that disease is much more destructive than powdery mildew. Look for many small half-inch or smaller sized angular dark spots on the leaf. This disease can be controlled if spotted in time. You will have probably 4 to 5 days from when you see the disease to when the vines may collapse if no control is applied. Outbreaks can be very localized rather than widespread in a region, so don’t just go by reports from other sources, look in your fields.
Conventional growers have many fungicides to choose from. Nova or Pristine work best if applied when powdery mildew is first observed. Start with one of these plus a protectant, then use the other 10 to14 days later, also with a protectant. If downy mildew should occur, then specific materials need to be incorporated into the spray schedule such as Acrobat, Curzate, Gavel, or Previcur Flex. Note that the strobilurins (Flint, Quadris, Cabrio) are not effective against powdery mildew.
Organic growers have many fungicides to choose from, too, although research by Dr. Meg McGrath on Long Island show that many are not very effective. The best results were obtained with sulfur (4 lb/acre Microthiol Disperss – this product is allowed by Vermont Organic Farmers although is not yet OMRI listed – check with your certifier before using it.) Be aware that sulfur can be phytotoxic on melons in hot weather. To be effective, applications need to be made every 7 to 10 days, or every 14 days on powdery mildew ‘resistant’ varieties.
NOW IS THE TIME TO TAKE SMALL FRUIT LEAF SAMPLES
Foliar analysis is the best way to determine the fertilizer needs of perennial fruits. For strawberries sample the first fully expanded leaves after renovation, within 6 weeks after harvest. For raspberries sample healthy leaves on non-fruiting canes in August. For blueberries sample healthy leaves between mid-July and the end of August. Always select undamaged leaves that have had good light exposure and represent the average condition of the planting. Avoid mixing leaves from different cultivars or plants of different ages. Select 50 leaves per sample, taken from at least 10 different plants across the sampling area. Gently wash off any soil or spray residues, if necessary, and allow leaves to dry. Place them in paper bag or box and mail to: UVM Ag Testing Lab, Carrigan Drive, Burlington VT 05405-0082. Enclose a check to ‘UVM Ag Testing Lab’ for $20 per sample with name of the field and your complete contact information.
WHAT ARE THOSE WHITE THINGS ON TOMATO HORNWORMS?
Tomato hornworm larvae are parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae that hatch from wasp eggs laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as many small white projections protruding from the hornworm’s body. Parasitized hornworms should be left in the field to conserve the beneficial parasitoids. The wasps will kill the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize.
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