Clark County has reported a massive spike in corn earworm (CEW) this week.

386 CEW moths caught during past week.

Other trapping locations have not reported an increase in activity yet (https://u.osu.edu/jasinski.4/pestvisualization/#linke). This annual caterpillar pest of sweet corn and tomato should have growers paying special attention to these crops for infestation, especially during the latter part of the season. Flights of CEW typically increase through the summer as the moth migrates into Ohio from southern states such as Louisiana, Texas and Mississippi. The caterpillar stage is known to attack silking corn and tomato fruit, especially when other susceptible hosts are not abundant.

CEW, aka tomato fruitworm, feeding on tomato.

Moths prefer to lay eggs on fresh sweetcorn silk and can hatch and enter the ear tip as quickly as two days under ideal weather conditions, where they are no longer susceptible to insecticide treatments. Treatments for this pest should be made based on number of moths per day and daily temperature threshold of 80F. Use the chart below to determine the recommended number of days between insecticide application to protect sweet corn as it enters silking. Insecticide options can be found in the Midwest Vegetable Production Guide, remember to rotate insecticide classes to avoid resistance (https://mwveguide.org).

CEW spray interval chart.

Want to learn more about monitoring for CEW? Check out this original video that reviews how to set up a trap to monitor for CEW (https://www.youtube.com/watch?v=W6b7OtUOo8Y&list=PL0HRPaZDLHyG53DPisl9iGTezcx815u-q&index=8).

There is also an updated version of how to monitor for several key moths in sweet corn on the OSU IPM YouTube channel https://youtu.be/X1jvQxx_fpc

CDM.ipmpipe map of pumpkin downy mildew reports, August 10, 2022

We have had a confirmed report today from Bill Holdsworth of Rupp Seeds of downy mildew on pumpkins in research plots near Wauseon, Ohio, in Fulton County. This is the first report of downy mildew on pumpkins, not only in Ohio but in the Great Lakes region and in fact a big swath of the Midwest and Northeast

CDM.ipmpipe map of cucumber downy mildew reports, August 10, 2022

(map on left). Compare this to the cucumber downy mildew map on the right, with widespread distribution. As a reminder, these maps are constructed from voluntary reports of downy mildew. The disease is likely more widespread than the maps show. Bill has also seen downy mildew on gourds in the area.

The downy mildew pathogen, Pseudoperonospora cubensis, exists as two clades. Clade 2 is quite specific to cucumbers and melons and tends to circulate early in the Great Lakes region, having possibly overwintered on cucumbers in greenhouses. It also makes its way up the Eastern US from southeastern states. Clade 1 has a broader host range, attacking all cucurbits, and also originates in the Southeast, moving up the through the eastern states. Due to typical wind currents from west to east, we don’t usually see clade 1 outbreaks in the Midwest until mid-August or September, when spores can be carried in storms that are remnants of hurricanes originating in the Southeast. We don’t know with certainty yet if the Fulton County outbreak was caused by clade 1 strains, but this is likely. We hope to conduct molecular tests to confirm the clade in the near future.

Downy mildew symptoms on a pumpkin leaf (top)

Downy mildew symptoms on the underside of a pumpkin leaf.

Downy mildew can be a bit harder to diagnose in pumpkins, squash and other Cucurbita species since the lesions may be smaller and not always crisply angular as in cucumbers. Downy mildew can also cause a lot of damage on pumpkins, squash, gourds and other Cucurbita spp.

Growers should be scouting all cucurbits for symptoms of downy mildew. The best time to do this is in the morning before 9 or 10 am before the lesions dry out and the sporangia disperse. If you find suspicious symptoms you may text me photos of the underside and top of symptomatic leaves (330-466-5249) and/or send us samples for confirmation.

Growers of any cucurbits throughout Ohio should apply appropriate protectant fungicides such as chlorothalanil (e.g. Bravo). Growers in Fulton County should begin a fungicide program with downy mildew-effective fungicides now. See my July 11 post for a list of recommended fungicides.

As noted by Sally Miller last week, bacterial wilt and yellow vine decline are being found in cucurbit fields across the state. There are two primary insects responsible for these outbreaks, the Striped cucumber beetle (Acalymma vittatum) and squash bug (Anasa tristis). I was just scouting some of my pumpkins this past week and counted 20 beetles in one flower! But sometimes looks can be deceiving as we can encounter as many as 4 different types of beetles in our cucurbit fields. It’s important to know what’s in your cucurbit since it could be the difference between making an insecticide application (or not). Below, I have included an image of different beetle species you may encounter in your cucurbit fields. As a reminder, we generally want to make an insecticide application when the striped cucumber beetle density exceeds 1 beetle/plant in a field. If you want information about specific products, check out my former post here.

Squash bugs are arguably easier to scout for since there aren’t many other insects that resemble them. However, we need to keep track of different squash bug life stages (shown below). Squash bug eggs are fairly diagnostic with a bright amber coloring. They are typically found along the midribs on the undersides of leaves. Those egg masses eventually give rise to nymphs which are powdery blue. Adults have a flattened appearance and are typically brown with alternating white and orange spots along their abdomen. Insecticide applications are warranted when squash bugs exceed a cumulative threshold of 1 egg mass, nymph or adult bug/ plant in a field.

Downy mildew on basil

Downy mildew was spotted in a garden in Wooster, Wayne County, Ohio and confirmed by Dr. Francesca Rotondo, interim director of the OSU Plant and Pest Diagnostic Clinic. This is the first report in Ohio this summer but it has likely been here for a few weeks. The pathogen, Peronospora belbahrii, is related to but different from the cucurbit downy mildew (CDM) pathogen, Pseudoperonospora cubensis. These pathogens don’t cross-infect hosts: P. belbahrii does not infect cucurbits and P. cubensis does not infect basil. However, their biology is similar; they are both obligate parasites that require living plant tissues to survive. They disappear from the outdoor environment in northern areas during the winter and are introduced the following spring or summer from infected plant material or via spores carried on wind currents and rain. Cucurbits or basil grown over the winter in greenhouses can be a source of inoculum. Last year we found basil plants with severe downy mildew symptoms in a big box store in Wooster. We tend to begin

Light microscope image of sporangia of the downy mildew pathogen Peronospora belbahrii. Image by Francesca Rotondo.

seeing basil downy mildew in Ohio in July or August. Rainy, cloudy weather favors spore (sporangia) transport and infection; the sporangia are sensitive to UV light and tend to be killed by sunshine.

Management of basil downy mildew, like CDM, is entirely preventative. There are resistant varieties and a number of fungicides and biologicals are available for conventional and organic production systems.  Fungicides and biologicals are only effective if applied before infection. Home gardeners should keep an eye on their basil plants and harvest non-diseased leaves as soon as downy mildew is observed. More specifics can be found in last year’s July 17 post.

Confirmed reports of cucurbit downy mildew. https://cdm.ipmpipe.org

Downy mildew developed in a commercial fresh market cucumber field in Huron County this past weekend. That makes five counties in northern Ohio with confirmed reports of downy mildew, all on cucumbers. It is likely that downy mildew is widely distributed in cucumbers in northern Ohio, but we are not always alerted to its appearance. Since our first report of downy mildew on cucumbers in Wayne County on July 13, it has been reported in several other fields, including one of our research plots in Wooster. So far there are no confirmed reports of downy mildew on melons, pumpkins, squash or other cucurbits in Ohio.

Downy mildew must be managed preventatively with resistant varieties (there are a few, see chart below) and more commonly with fungicides. In our experience, fungicides applied after infection are significantly less effective than the same ones applied before infection. Cucumber and melon growers in northern Ohio should be applying effective fungicides  on a 5-7 day schedule depending on the label requirements. Growers elsewhere in the state should be applying protectants such as chlorothalanil, e.g. Bravo, to all cucurbits. This will also help prevent other diseases such as Alternaria leaf spot and gummy stem blight. More details and a fungicide efficacy table can be found here.

For over 20 years the pumpkin field day has been a source of production and pest management information for both new and experienced growers. This year we will be adding some flair as we begin to tackle the production and pest management issues surrounding the popular trend of sunflower fields for photographs and cut flowers as an additional source of revenue on diversified farms. So if you want to learn about two popular fall attractions, pumpkins and sunflowers, this is a field day that can’t be missed.

Pumpkin and sunflower

The field day will be divided roughly in half, with the first hour focused on sunflower topics ranging from grower experiences in production (Matt Sullivan, grower) to impacts from the ag tourism perspective (Kate Hornyak, OSU). A nine-hybrid sunflower demo strip trial will be in various stages of bloom for attendees to walk through and examine.

The second hour will focus on pumpkins, starting off with managing pollinators in cucurbits (Ashley Leach, OSU), foliar fertilizers and plant nutrition (Bryan Reed, Sunrise) and then a review of powdery mildew fungicide management and a walk through the 24 hybrid trial (Jim Jasinski, OSU).

The field day will be held at the Western Ag Research Station, 7721 S. Charleston Pike, South Charleston Ohio. The field day will begin promptly at 5:30 PM and end at 7:30 PM. Pre-registration is required for attendance and there is a $5 charge per person for handouts and refreshments (and likely a few sunflowers). For more information contact Jim Jasinski, Jasinski.4@osu.edu.

Pre-register at this link: https://go.osu.edu/pumpsun22

More details are listed on the attached flyer. Hope to see you there!

Pumpkin and Sunflower 2022 Flyer