VegNet Vol. 13, No. 8. June 15, 2006
Ohio State University Extension Vegetable Crops
On the WEB at:  http://vegnet.osu.edu
If experiencing problems receiving this fax, Call 614-292-3857

In This Issue

1. Downy Mildew Found in MI cucumbers

2. High Tunnels

3. Stewart’s Bacterial Wilt in sweet corn.

4. Soybean aphid trap network.

5. Crop Report, Meigs County Vegetables in Pictures

Downy Mildew Confirmed in Michigan Cucumbers Sally Miller

Downy mildew was confirmed in two slicing cucumber fields (16 acres) in SE Michigan (Monroe county) on June 9.   The Michigan sighting was unexpectedly early, on field plants under low tunnels. It is not clear where the disease originated, and so far it has not been confirmed in other fields in Michigan. Cantaloupes growing nearby were not visibly diseased. There have been no confirmed reports of downy mildew on cucumber or other cucurbit crops in Ohio.  As of Wednesday June 13 the predicted risk of downy mildew for SE Michigan and NW Ohio is "weakly moderate". The predictions can be found on the North American Plant Disease Forecast Center Cucurbit Downy Mildew website (http://www.ces.ncsu.edu/depts/pp/cucurbit/forecasts/c060613.php). 

Downy mildew symptoms can be confused with those of other diseases, environmental damage and chemical burns. If you find what looks like downy mildew in cucurbit fields, send a sample (overnight delivery) for confirmation to Sally Miller or Melanie Ivey, Department of Plant Pathology, The Ohio State University, OARDC, 1680 Madison Ave., Wooster. OH 44691, ph. 330-263-3838, or to the C. Wayne Ellett Plant and Pest Diagnostic Clinic, OSU, Kottman Hall, 2021 Coffey Road, Columbus, OH 43210, ph. 614-292-5006 (c/o Nancy Taylor).

A “weakly moderate” risk means that under the current dry conditions, in the absence of any observed downy mildew, the spores of the downy mildew pathogen are not likely to move around for long distances. Cucurbit fields need to be carefully scouted for downy mildew, especially should rainy conditions occur or threaten. When the predicted risk is high and/or the disease is found in the field, a protectant fungicide such as chlorothalanil (Bravo, Equus, etc.) or EBDC (maneb, mancozeb) should be applied.  Growers may consider additional fungicides if the disease progresses and rainy conditions persist. Research conducted at Michigan State University suggests that Previcur Flex (1.2 pt.) + protectant alternated with Tanos 50 DF (8 oz.) + protectant provides good control of downy mildew in cucurbits. Please see http://ohioline.osu.edu/b672/ for current recommendations. Since the disease has already been found in Michigan, growers are recommended to begin fungicide applications at this time.

Interested in High Tunnels

Haygrove Tunnels will co-host several "Grower to Grower" meetings at farms in eleven US states and Ontario. The meetings are scheduled during the growing season, so growers can see for themselves just how much difference Haygroves make, and they start at 6 PM unless otherwise noted. Some of the meetings closest to us in OH are:

July 6 - 11:30AM Michigan State University, Clarksville MI, cherries

July 11 – 6-9 PM, Schacht Farm, 5950 Shannon Rd., Canal Winchester OH, 43110; tomatoes, strawberries, mustard mulch.

July 14 - 2:30PM Cedar Meadow Farm, Holtwood PA, tomatoes, raspberries (Haygrove meeting in conjunction with a no-till and cover crop field day)

July 14 - 6PM Riverview Produce, Leola PA, heirloom tomatoes, various trial crops

July 19 - 6PM Penn State University, Rock Springs PA, PSU high tunnel day (no Haygrove tunnels - poly trials, Haygrove’s Luminance poly vs others)

For a complete schedule of the Grower to Grower meetings, go to the following link: http://www.haygrove.co.uk/docs/growerToGrowerUS.pdf

For some background information on the company go to the link below:

http://www.haygrove.co.uk/introPage.asp?article=98#__anchor3c

Stewarts Bacterial Wilt in Sweet Corn

Stewart’s Bacterial wilt is showing up in one sweet corn variety. About 10 to 20% of the plants are infected. There are no problems with most other varieties.

Symptoms: Young plants that become diseased usually wilt and die. Affected young plants develop yellow to white stripes on the lower leaves. These plants generally produce several tillers. The plants that do not die are stunted and usually produce no ears. Leaf blight can be recognized as long, pale green streaks on leaves. As the streaks enlarge, portions turn pale yellow and eventually become brown. Streaks may run the entire length of the leaf and the margins of the streaks are wavy. A few characteristic lesions may be seen early in the season, but numerous lesions are usually not detected until after tasseling. This increase in susceptibility after tasseling is probably a physiological response to the reproductive phase of the corn plant

Leaves showing white yellow stripes

Stripes turn brown, plants are severely stunted and the center dies

Soybean aphid suction trap network for vegetable and field crop growers Provided by Hanah Stevens and Jim Jasinski
The following is an article written by Dr. Chris DiFonzo, Michigan State University field crops entomologist, for the Field Crop CAT Alert. The article discusses details of a multi-state soybean aphid trapping network with information NAN (New Agriculture Network) readers can use.

Why should vegetable growers care about this network? In previous years, large numbers of soybean aphids taking flight from soybean fields in late July and early August are thought to have spread viruses to a variety of vegetable crops (including vine crops, snap beans and peppers). Soybean aphids, like other aphid species, find new fields by flying, landing and “tasting” plants with their mouthparts and then flying on if the plant is not to their liking. During this “tasting” behavior, plant viruses are both acquired and spread. The “tasting” (and consequent virus spread) occurs so quickly that insecticides have no impact on virus transmission. But, by being aware of the timing and size of the aphid flight in late July and August, growers can avoid planting virus susceptible varieties when aphid flight is high. The web site given in the article (http://www.ncipmc.org/traps/) shows up-to-date aphid trap catch numbers for the (soon to be) five locations in Michigan.

Northcentral Regional Aphid Suction Trap Network was turned on last week in at least eight states. As in 2005, Michigan has three trapping locations that cover a north-south transect: MSUs Saginaw Valley Bean and Beet Research Farm in Saginaw County; the MSU Entomology Farm in Ingham County; and the Kellogg Biological Station in Kalamazoo County. By the end of June, we will set up two new locations, one at the MSU Extension Office in Monroe County to cover southeast Michigan and another in western Michigan in Oceana County. Monroe County has a high population of buckthorn, the overwintering host for soybean aphid; it experienced heavy, early aphid infestation in 2005, and thus may benefit from trapping information. The location in Oceana County is specifically targeted to provide information to vegetable growers in Western Michigan, where soybean aphid is implicated in virus spread.

The traps suck in migrating insects, including winged aphids, flying over 20 feet above the ground. The insects end up in a jar of antifreeze just above the fan in the base of the trap. Sample bottles are changed weekly, and mailed to the University of Illinois where aphids are removed, identified and counted. The soybean aphid counts are posted on a web site, http://www.ncipmc.org/traps/, where you can view individual traps from each of the eight states. There are currently 33 traps on the network, plus five to six more that will come on line in June.
How can you use the suction trap data?
In early to mid-July, increasing flight tells you that winged soybean aphids are being produced in early-infested fields and are now dispersing across the landscape. These infested fields could be local, in another part of the state or even in a neighboring state. This means that previously uninfested, low-infested fields or seed-treated fields may get an influx of landing aphids that leave babies behind. This is how fields in areas that lack buckthorn (for example, many locations in southwest Michigan) get infested in July.
Later in the season, in late July and early August, increases in flight often time with peak infestations in soybean fields. For example, last season (see the 2005 data at http://www.ncipmc.org/traps), tremendous numbers of soybean aphid were trapped in early to mid-August, when aphid populations peaked in nearby fields. Such heavy aphid flights increase the risk of reinfestation in previously-sprayed fields we certainly experienced that frustrating situation in 2005.
In the last four years, heavy aphid flights in late July to early August coincided with virus infection in vegetable crops in Michigan. The suction traps can alert growers to a potential virus threat and may eventually help vegetable growers make decisions about late-plantings, for example, variety selection.

At the end of the season, the suction traps play their most important role, potentially predicting next year’s soybean population. Suction traps catch the winged males and females that leave soybean and go back to buckthorn, where soybean aphid overwinters.
In Illinois, the number of fall migrants caught in suction traps correctly predicted the next year’s aphid population (outbreak versus no outbreak) in four out of four seasons, including 2005. The 2005 season was the first year for the Regional network, across eight states. At the end of 2005, some areas (such as Michigan) had low fall trap catches; others (for example Minnesota) had high fall flights. June 2006 is a critical test for the predictability of the traps in theory, Michigan should have low colonization this spring, and Minnesota should have early, heavier colonization. Stayed tuned!

Crop Reports –Meigs County Vegetables June 13, 2006

Transplanted sweet corn on black plastic with trickle is about 10-14 days from harvest if warm weather continues.

Tomato harvest (left) as well as slicing cucumber (right) is close as long as temperatures and moisture remains favorable.

Notice the effect of plastic mulch (left) and bare ground (right) on melon growth.

Washington county agent Eric Barrett and Meigs County agent Hal Kneen (not shown) examine the effect of blue plastic mulch on melon growth.