Recognize and Mitigate Crop Heat Stress

Recent conditions in some areas (soaked soil, fog- and dew-filled mornings, high daytime humidity) can give a different impression about the season so far than weather data at https://www.oardc.ohio-state.edu/weather1/ and various forecasts. Temperature, rainfall, and other data are collected around the clock at OSU vegetable (and other) research sites in Fremont, Celeryville, Wooster, and Piketon and have been for decades. So far in 2021, these four locations have accumulated less precipitation and more growing degree days (GDD) than their historical averages. Also, climate and weather authorities reported on June 11 that the Upper Midwest, including Ohio, is set to experience hot, droughty conditions. Most agree that a dry year is less problematic than a wet one — provided irrigation is possible. However, it can be difficult for vegetable growers to escape the unwanted effects of excessively high temperatures. A way to separate potentially minor, moderate, and severe heat stress, example effects of moderate-severe heat stress, and main strategies for mitigating heat stress during production are summarized below.

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Early Season Cucurbit Pests – Cucumber Beetles & Bacterial Wilt

In the next 2-3 weeks, pumpkin, squash, melon and cucumber growers looking for an early crop will start direct seeding in the field or preparing seed flats for later transplanting out in the field. One of the perennial pest’s growers run into is the striped cucumber beetle which can attack seedling plants and chew them nearly to the ground. In addition to the physical damage the beetles can inflict, there is also a chance that some can transmit bacterial wilt to the plant which will prevent it from setting mature fruit.

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Cucurbit Downy Mildew is Spreading in Ohio Despite Hot Weather

Micrograph of a tape mount of spores and sporangiophores of the cucurbit downy mildew pathogen from cucumber leaves. Photo by Francesca Rotondo.

Downy mildew continues to spread in Ohio cucumbers despite the hot and mostly dry weather.  Frank Becker, OSU Extension Wayne County IPM Program Coordinator, brought cucumber leaves with downy mildew symptoms to to our Vegetable Pathology Lab on July 23 for confirmation.

We do this by placing a piece of scotch tape on the underside of a leaf lesion then transferring to tape to a glass slide and looking for characteristic spores and sporangiophores (branched, threadlike structures that produce the spores) under a microscope. The samples came from commercial cucumber fields in Wooster and Apple Creek in Wayne County, and both were positive for downy mildew.

Although we have confirmed reports in only Medina and Wayne counties, cucurbit downy mildew is likely present in most northern Ohio counties.  The map of downy mildew reports shows confirmed cases in Ontario, Michigan and western New York as well. All of these reports are from cucumbers; this clade, or strain of the pathogen affects cucumbers and cantaloupe, but not squash or pumpkins. We don’t expect downy mildew on squash and pumpkins until the other known clade, which has a broader host range, migrates to the Midwest from the Southeast.

Cucurbit downy mildew as of July 24, 2020. cdm.ipmpipe.org.

 

 

 

 

 

 

 

 

Fungicide recommendations are posted here.  If you suspect downy mildew in any cucurbit, please send us a sample.  This will help us track the disease and provide early warnings to growers to enable timely protection of cucurbit crops. Our diagnostic service is free to commercial growers in Ohio; gardeners may also send cucurbit downy mildew samples to us free of charge.  Instructions for sample submission are posted here.

Downy mildew in cucumber.

 

 

Ready to manage spider mites?

With the current hot and dry weather conditions in Ohio, we expect to hear reports of spider mite outbreaks on specialty crops. Because mites are tiny, they are often overlooked or misdiagnosed as a disease. Infested leaves have fine webbing on the leaf undersides. Tomato leaves damaged by spider mites usually have yellow blotches, while bean leaves show white stipples or pin-prick markings from mite feeding. Pumpkins can tolerate moderate levels of mites, but watermelons are more sensitive to injury from mite feeding. A simple method of diagnosing spider mites is to shake leaves over a piece of paper and look for moving specks that are visible to the naked eye. A closer look with a magnifier can show the tiny mites that are white, marked with two large dark spots on the middle of the body.

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Another Cucumber Downy Mildew Outbreak in MI – and Closer to Home

Outbreaks of cucumber downy mildew on two commercial farms in Monroe County, MI were detected on June 29. Monroe County is in southeast Michigan and borders Ohio’s Lucas County. In addition, spores of the downy mildew pathogen have been captured in spore traps in four Michigan counties, so downy mildew is ramping up and very likely to be in cucumbers in northern Ohio at this time.

Downy mildew sporulation on underside of a cucumber leaf.

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Early Season Cucurbit Pests

Jim Jasinski, Dept. of Extension, Celeste Welty, Dept. of Entomology

Although it’s been wet over most of the state recently, the temperatures are warming up allowing growers to get into their fields to direct seed or transplant pumpkin, squash, melon and cucumbers through May and into June. By now most decisions about how to manage key early season pests may have already been made with the purchase of systemic seed treatment or plans to treat transplant water using neonicotinoid insecticides. Some growers may have decided to forego systemic treatments and rely on scouting and treatment using foliar insecticides when thresholds are exceeded.

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Beware of armyworm on early sweet corn and other crops!

 

Originally posted in the VegNet Newsletter on May 17, 2020

We have detected an extremely large population of armyworm moths in Columbus during the past week. This pest prefers to feed on grasses, including corn, wheat, rye, and grassy weeds, but if those plants are in shortage and if populations of armyworm are large, it can infest other crops including alfalfa, beans, cabbage, cucumbers, lettuces, onions, peppers, and radishes. Infestation can be worse in no-till fields than in tilled fields. Any early-planted fields of these crops should be scouted for presence of armyworm. Scouting is best done near dawn or dusk because armyworm larvae are nocturnal and hide in the soil during the day. The name armyworm is given because of the ability of older larvae to form large aggregations that move together from field to field. Infestations can appear quite suddenly in a field, and much damage can occur in a short period of time.

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