REPORTS FROM THE FIELD (As of August 22)
Powdery Mildew is showing up throughout the state on cucurbits. (PM infection can increase susceptibility to diseases that cause pumpkin and squash handles to rot in storage. Protective sprays are usually necessary to control PM into the latter part of the growing season, but fungicides should be rotated to avoid resistance. There are 2 relatively new, environmentally friendly, fungicides to consider for next year's rotation: Quadris and Armicarb.) Many vine crops are showing browning of leaves. According to Dr. Tom Zitter at Cornell, much of this is due to heat stress. Older leaves in the center of the plant will show this stress first. Another cucurbit disease, Phytophthera, has spread rapidly on a farm in Essex, destroying an entire pumpkin field. This disease is spread through water, so try to prevent standing water in your fields. Clubroot has been a problem in fields at several locations this year. This pathogen infects the root systems of Brassicas, forming thick and swollen club?like growths. Above-ground symptoms are stunted plant growth, yellowing of the lower leaves, and wilting and death of the plant. Plants may not show symptoms until nearing maturity. Clubroot stays in the soil for many years, and cruciferous weeds such as mustard are also hosts. Management includes rotation out of Brassicas for at least 3 years, control of weed hosts, and rasing soil pH to 7.3. Continue keeping an eye on the ground for: Colorado Potato Beetle, Striped/Spotted Cucumber Beetles, Tarnished Plant Bug, Imported Cabbage Worm, Diamondback Moth and Cabbage Looper, Thrips, European Corn Borer and Corn Earworm, Hornworms, and Late Blight. (mostly from Eye on the Ground report, Pam Adams, IPM Scout.)
Rain, shortening days and cooler nights making life a bit easier here by giving us a our first real break from irrigating all summer. Field laborers are jumping ship this week to start school, so we are trying to wrap up repair and construction projects. Erratic ripening in corn blocks makes picking harder, and the drought looks as though it will make the latest blocks planted ripen earlier than we had hoped for. Our scout has alerted us to the fact earworm numbers in the Heliothis traps have jumped and told us to spray every 5 days. Tomato varieties all are ripening later and together despite the fact they were pampered with drip. Early blight getting in there as well. Pumpkins and squash ripening early as also noted in UMass vegetable notes. We will start harvesting before labor day. Strawberries look pretty good, especially renovated beds, very little leaf spot. Without the summer labor the next month will be tough physically on the few of us that remain. (E. Hartland)
Recent rains left the crops looking much better. We've lost our onions and at least half of the winter squash, but for the most part we're still hanging in there with other crops. Incredible pressure from deer this year. They seem to be coming out of the woods where there's little food and water. We see their tracks around the irrigation pond and then of course in the carrots, beets, and lettuce where they are nibbling. In one far-off field they ate a third of an acre of broccoli transplants in one day. Aphids are starting to show up on brassicas. Leafhoppers are severe in many crops. The potatoes died very early but the reds have decent size anyway. Watermelons are all ripe and picked - a very short and somewhat sweet season. The corn is doing very well. Overall, very relieved with the recent rain and hope it is the start of a new trend. (Amherst MA)
We are starting to cover crop things now for the fall. We will use rye of course and some winter wheat. I'm beginning to hate rye since it is so stubborn to plow in. We would like to fix some nitrogen, but would also just like to create some useful sod to plow in next spring. Water is still a major issue despite rain. Put up two lines of wire off the main charger for deer fence, and it seems to be working. Have been trying direct seeding of mesclun but it has a lot of drawbacks, mainly weeds. Guess I'll go back to using soil blocks keep buying lots of potting mix. (Charlotte)
PUMPKIN VIRUS PRIMER (adapted from Ohio State
Watermelon mosaic virus (WMV, formerly called WMV-2) was by far the most common virus detected when we ran ELISA tests on thousands of pumpkin leaf samples from across Ohio from 1994 to 1996. We occasionally found cucumber mosaic virus, squash mosaic virus, and papaya ringspot virus (formerly called WMV-1). We never detected zucchini yellow mosaic virus. Aphids are the vectors of all of these viruses, except for squash mosaic virus which is vectored by cucumber beetles and which can be seed borne. Although most aphids are wingless, all aphid species have wings at some times in the season. It is the winged aphids that start a new infestation in fields. Viruses like WMV are transmitted quickly while the aphid is probing the leaf with its mouthparts, before it picks up the lethal dose of insecticide. Insecticides can do a good job of killing aphids that colonize pumpkin plants, that is, ones that stay to feed and reproduce. Insecticides can also do a good job of killing non?colonizer aphids, which are the ones that land in pumpkins take several tastes, then fly on to find more preferred hosts. BUT, in either case, the virus is transmitted before the aphids die. Usually a field with virus will still produce a harvestable crop. Most Ohio fields that get WMV start to show leaf symptoms (leaves twisted, warty, mottled light green and dark green color) in late July and symptoms are usually widespread by mid?August. Many fruit that were set before this time will show only mild virus symptoms: mostly uneven coloration and light green circular rings. Fruit set usually still occurs after virus infection but fruit symptoms are more severe: lumpy fruit with very uneven coloration.
The most common aphid species that land in pumpkin
fields in Ohio are corn leaf aphid, artichoke aphid, green peach aphid,
turnip aphid, melon aphid, cowpea aphid, potato aphid, and sunflower aphid.
We have tested several of these for their ability to transmit WMV to pumpkins.
We found that green peach aphid and melon aphid are good vectors, artichoke
aphid and potato aphid are weak vectors, and corn leaf aphid is unable
to vector this virus. We do not know for sure where the aphids pick up
the virus but we think that there is a reservoir of virus in some species
of local plants. We have tested about 50 species of plants for WMV. Most
plants tested were perennial weeds, along with some perennial crops and annual weeds. The plants that were found to contain WMV were shepherd's purse, Virginia pepperweed, field bindweed, dandelion, purple deadnettle, and goldenrod. Growing resistant varieties seems to be the only way to manage viruses. Several WMV-resistant pumpkin varieties are under development and should be commercially available within 1 to 2 years.
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