Cool, rainy conditions have given way to heat and humidity. Some vegetables planted before the change in weather are struggling, even under row cover. It appears they didnít develop many roots when it was colder and now they are having trouble coping with the heat. Once they adjust they should be OK. Precipitation has varied around the state, as it usually does. In many locations the soil surface is dry so irrigation is needed on small plants even though thereís moisture deeper in the soil.
Humid, rainy weather may lead to disease problems. As much as possible, avoid spreading bacterial pathogens by not working in crops when leaves are wet. Be prepared to harvest crops fast and frequently when ripe and cool them down right away. Keep an eye out for Phytophthora root disease where soil has not drained well and destroy infected plants promptly.
Some greenhouse tomatoes have been showing unusual growth, with leaf deformity and raised leaf ribs, often a sign of virus but none has been detected in a crop that was tested. Perhaps itís a reaction to the weather? Bacterial canker has been found in one tomato house. Plan to buy hot water seed or treat it yourself in coming years.
Market trends suggest increasing consumer interest in fresh, local, healthy produce. Donít let the weather get you down; be positive with your customers.
STRAWBERRY PEST UPDATE
(adapted from David Handley, UMaine Extension)
Strawberry clipper has been active in fields where plants still have a lot of unopened flower buds. Once most flowers in a field have opened, clipper is no longer a threat to the crop and attention should focus on tarnished plant bug. Be aware that clipper may move onto raspberry buds once strawberry buds have opened and no longer offer good egg-laying sites. Check raspberry flower clusters for clipped buds and live clippers. Insecticide sprays to control raspberry fruit worm adults, which are also active at this time, should provide some control of clipper as well. Products registered for clipper on raspberries include Sevin XLR Plus, and for organic growers Aza-Direct or PyGanic.
Tarnished plant bug nymphs are now active in fields, they are small, yellow-green insects. Scout for them often because they may appear quickly in warm weather. They feed on strawberry flowers, causing berries to have seedy ends. To scout, shake 30 flower clusters (6 clusters in 5 different locations) over a white plate. If 4 or more of the clusters sampled have any nymphs, control measures should be taken. Registered sprays include Brigade, Danitol, or Thiodan. PyGanic can be used by organic growers.
Twospotted spider mites are present in most fields, but remain mostly below the spray threshold. Populations may soon rise due to warm temperatures, and because insecticides applied for other pests can also eliminate the natural predators of spider mites. To scout for mites collect 60 leaves from various locations in the field and examine the undersides. Mites are very small so a hand lens is needed to see them. If mite populations are still low consider introducing predatory mites right away. Miticides labeled for strawberries include Vendex, Savey, Kelthane, Agri-mek and Zeal. Organic growers can use JMS Stylet Oil; direct contact is needed with mites and eggs to kill them.
Spittlebugs are appearing in some strawberry fields. These insects usually pose no threat to the plants, but the frothy spittle they cover themselves with for protection can annoy pickers. The spittlebug overwinters in the egg stage and the small, yellow-orange nymphs emerge in late May and can be found in the spittle masses. Scout during bloom by randomly inspecting 5 one-square-foot areas per field every week. Inspect the crowns, leaf bases, leaf stems, and flower stems. If the average number of spittle masses is more than two per square foot, a treatment may be warranted. Spittlebugs tend to be a greater problem in weedy fields.
Many strawberry plantings are still at a critical stage to protect
the fruit against gray mold. Two to three sprays of fungicide from early
bloom through petal fall are usually needed to give good protection against
this disease. The plentiful moisture still present in most fields will
make good coverage essential. If you tank mix insecticides and fungicides,
avoid spraying when bees are active. Be sure to rotate the fungicide materials
you use for gray mold to prevent the development of resistance.
Leather rot is a concern in fields that have had standing water. Rain and irrigation will promote infection by splashing the fungus onto the flowers and fruit. Maturing fruit in contact with wet soil can also be infected. Fruits may be affected at all stages from blossom to maturity. Clean straw mulch placed under plants and between rows keeps maturing fruit from getting rain-splashed soil on the surface.
Anthracnose fruit rot is also a concern because it is favored by warm, humid conditions and can spread rapidly during rains or frequent irrigation. Anthracnose fruit rot can be identified by black sunken lesions on the berries. It can become widespread very suddenly in a field. Fungicides that offer control of anthracnose include Abound, Cabrio and Switch.
Powdery mildew can be stimulated by periods of humid weather. The
most obvious indication of this fungus is the upward curling of the leaves.
Purple or reddish blotches, and/or white, powdery growth may be observed
on the undersides of the leaves. Mildew infections weaken plants and can
reduce yield the following year. Some varieties are more susceptible than
others, for example Northeaster and Annapolis, while Mira and
Mesabe are thought to be resistant. Quadris, Captan, Pristine, Cabrio, Topsin-M and Stylet oil are presently registered to control powdery mildew. Organic growers can use Armicarb-O.
VEGETABLE PEST UPDATE
(adapted from John Mishanec, Cornell Extension)
European corn borer (ECB) started flying the first week of June and now with warm weather is found in large numbers in many areas. Corn that was under plastic and has been uncovered will attract ECB egg deposition. Most growers using floating row cover still have their corn covered up. If it is uncovered while the ECB flight is still going strong, moths will be attracted to that corn as well. If you can, keep the row cover on long enough to avoid the ECB flight.
Cucumber beetles are out in many areas. Inspect your crops, looking first in the flowers. Smaller plants are more prone to damage than larger plants and you also have to worry about bacterial wilt carried by the beetles. Pumpkins, cucumber and melons are very susceptible to bacterial wilt so scout these crops twice weekly. The threshold is one beetle per plant for susceptible plants. Until they have 4 to 6 leaves, pumpkins are extremely susceptible to wilt. Fortunately, not all farms have bacterial wilt problems. If you had this problem last year, or if it has been a problem in your area, it may be wise to apply controls at the one beetle per plant threshold. If you have not had a problem with wilt, you may want to hold off spraying the beetles. Other vine crops can have a five beetle per plant threshold as they are not susceptible to bacterial wilt. Be sure to check under row covers for cucumber beetle and flea beetle. Organic growers can treat transplants with Surround before setting n the field, or apply PyGanic after that. Conventional growers can use Admire at planting or spray Capture, Asana or several other materials once beetles appear.
Flea beetles can be found in high numbers in most crucifer fields.
When transplants and seedlings are small, they are more susceptible to
serious damage. About the best control for flea beetle for organic
growers will be row cover applied before the beetles emerged. Do
not put row cover over your crops now as this will just trap the beetles
with the plants. Growers using harder products can use Sevin and
get very good results. Do not spray Sevin early in the morning while
bees are around.
Colorado potato beetle (CPB) adults are out and laying eggs but larvae may not have hatched yet. Scout the crop and flag 10 leaves with egg masses on them bright yarn or tape. Watch these eggs and when the first mass hatched apply B.t. like M-Trak or Novodor because those products only work on the small larvae (Note: no B.t. for CPB is currently approved for organic use). If using a hard product like Provado or Asana, than you can wait till those first larvae are about the size as the hard shell parents. You can also wait longer if using Entrust (organic) or SpinTor than with B.t. since these products kill larger larvae. Because the ground is warming up slowly, adult CPB's are emerging slowly. This will cause an overlap of generations in the field and can be difficult to control without multiple applications of insecticide; more reason to make the first application when it will do the most good.
Leafhoppers come up from the south on thunderstorms but generally are not found this early. Organic growers have few good control options except floating row cover although PyGanic is labeled. Leafhopper sucks on the underside of the leaves and can cause economic yield loss without being visible. Keep an eye on crops by scouting them regularly, especially potatoes and beans. Adult hoppers are about a quarter inch long and nymphs are a little smaller, pail green in color and jump when disturbed. If the plants are tall enough to flop over, shake them and then flop the plant to the other side. You will see the hoppers on the ground. Treatment threshold is one adult or 15 nymphs per 50 potato leaves.
Mention of pesticides is for information purposes only, no endorsement is intended nor is discrimination against products not mentioned. Always read and follow the label. Organic growers check with your certifying agent before applying any material to a crop. For a more complete listing of materials labeled for different crops and pests, consult the New England vegetable and small fruit management guides, available from my office, or on-line. Go to www.uvm.edu/vtvegandberry and click on pest management. There are also links to Extension recommendations from other regions.
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