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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Upcoming Session to Focus on Long-term Success in High Tunnel Production

Originally posted in the VegNet Newsletter

Investments in high tunnels and high tunnel production are among the most significant growers can make, especially if the tunnels are stationary (not designed to move) and income from the tunnels is critical to the farm. Getting the most from tunnels from the start and over the long run is important. A session summarizing steps toward that goal will be held on Thursday April 23, beginning at 12 PM ET. The session is part of the OSUE Ag Madness series (https://go.osu.edu/agmadness) and will focus on major challenges and emerging opportunities in high tunnel production. Specific topics will include soil health, and new crops and high tunnel technologies — information for all high tunnel users, regardless of experience. Please see https://agnr.osu.edu/events/agriculture-and-natural-resources-madness to connect and contact Matt Kleinhenz (kleinhenz.1@osu.edu; 330.263.3810) for information. We look forward to seeing you there!

Spring is In Sight

Authors Carri Jagger, Published on February 10, 2020
Originally posted on the Buckeye Yard and Garden OnLine
It's time to start thinking about starting seeds for the vegetable garden

This has been a long, unpredictable, wet winter.  Thank goodness spring is in sight, Thursday March 19th will be the first day of spring.  With this being said, it’s time to start thinking about planning vegetable gardens.  If starting a new garden, soil testing the site where the garden will go is a good idea.  If it is an existing garden and the soil has never been tested, now would be a good time to think about testing it.  Your local OSU Extension office can help you with soil testing.

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