This article was excerpted from the CORN newsletter #19 and written by Alyssa Essman, Assistant Professor, Extension Field Crop Weed Specialist, Dept. of Horticulture and Crop Science.

We’re entering a period of hot, dry weather and the long-term forecast for this season suggests that these conditions are likely to persist during the summer and through harvest. With variable planting dates across the state, there is also a range in current crop growth stages and overall status, which means there are also different weed management activities taking place over the next month. There are some considerations to keep in mind as we aim to manage weeds when temperatures are high, and rainfall is scarce.

• Residual Herbicides – The incorporation or activation of residual herbicides can be insufficient in areas that receive less than ~ 0.5 to 1 inch of rainfall. Without some sort of incorporation or activating rainfall, the product does not enter the soil solution and is not available for uptake by germinating weeds. A layered residual strategy for the control of waterhemp is still recommended, especially where crops were planted early and preemergence herbicides are starting to decrease in concentration and lose efficacy. Rain will still be needed to incorporate these later-applied residual herbicides into the soil profile for maximum efficacy.

• POST Applications – Plants respond to drought stress in part by increasing the thickness of the cuticle, or the waxy outer layer of the leaf, to preserve water. This can result in decreased herbicide absorption, and translocation and metabolism within the plant are also affected. Systemic herbicides are especially at risk of reduced efficacy in these conditions. The use of the right adjuvant product and rate can help to increase absorption by improving leaf coverage and product uptake. Follow the label and herbicide/adjuvant manufacturer recommendations to determine the best adjuvant type and rate in these conditions. Some labels also include specific information related to applications in dry weather. Be aware that an increase in activity from the use of adjuvants can also lead to increased crop injury, and that applications early or late in the day may reduce the risk of injury. Contact herbicides are also more active when applied during hot weather, and crop injury from applications of these products may increase as well. Where residual herbicides were less effective due to lack of rainfall, a two-pass POST program should be considered to manage the potentially higher weed densities.

• Weed Emergence – Dry conditions can delay the emergence of weeds to some degree, especially those in the upper portion of the soil, and those that emerge from smaller seeds. Larger seeded species and those at lower depths will be less affected, as they have more energy reserves and access to more water for imbibition and growth, respectively. In dry weather patterns, weed emergence flushes may occur periodically following rainfall events.

• To Wait or Not to Wait – One question that often comes in when rainfall is limited is whether it’s better to apply POST herbicides soon, when weeds are smaller, or to wait until after a rain event and the potential following flush of weed emergence. Weeds are most effectively controlled when they are smaller and are actively growing. Drought and heat stress can impede control efforts and herbicide efficacy, and large weeds are more difficult to control. This is especially true if the stress-inducing conditions persist and weeds “harden off”. For this reason, it is a good strategy to wait for the extremely high temperatures to pass before making an application, for greater crop safety and herbicide efficacy, and to ensure weeds are actively growing. However, it’s not necessarily better to wait for a rain before making a POST pass. As mentioned, plants that persist through hot and dry weather often produce thicker cuticles, and it can be difficult for herbicides to get into the plant and be effective. For this reason, it might be best to spray when weeds are as small as possible unless there is some definite rain in the forecast.

The Integrated Pest Management Program along with OSU Extension educators across the state are monitoring five key pests this season. Monitoring sites are set up on farmer’s fields across the state and will be updated weekly.

Brown Marmorated Stink Bug – This insect will not be monitored for until late July though it is currently active in a broad range of specialty crops.

Spotted wing Drosophila – A total of three sites have been set up in Greene and Ross counties. SWD has not been reported or detected at any sites but growers with ripening brambles, blueberries, peaches and other soft skinned fruit should be aware of this pest so that proper management can be started when detected.

European corn borer – Two sites are set up in South Charleston (Clark Co.) and Fremont (Sandusky Co.), both reporting zero (0) moths captured. Additional sites should start reporting next week.

Corn earworm – Four sites are set up in Clark, Sandusky, Fayette and Crawford counties. Clark county trapped fewer this week than the previous week (28 moth to 9 moths). The other three sites reported capturing zero (0) CEW moths this past week.

Squash vine borer – There are eight sites currently trapping for this pest in Clark, Greene, Ross, Seneca and Morrow, Summit and Williams counties. Clark, Greene and Ross sites are reporting low single digit captures of SVB moths; the other four counties reported capturing zero (0) moths. Expect moth captures to go up this next week.

Growers can access and view the monitoring data directly at this site.
https://docs.google.com/spreadsheets/d/1T4Uk8VKH-fY4qms4FlEwQvz8o1Lxk-t8LLHVz97kxNU/edit?usp=sharing

This edition of the OSU Extension Fruit & Vegetable Report was created using field observations and expertise from the following OSU Extension staff: Mark Badertscher, Frank Becker, Thomas Becker, Ed Brown, Chris Galbraith, Melanie Ivey, Matt Kleinhenz, Ashley Leach, Logan Minter, Gigi Neal, Sabrina Schirtzinger, Ryan Slaughter

Vegetables

A common trend this spring is the delayed planting in many parts of the state due to consistent rainfall that held up field work. Transplants that have been held onto for too long may become rootbound and stressed, exacerbating transplant shock and generally delaying growth and development. With that said, conditions have been dry in other parts of the state such as SE Ohio and could benefit from more rain at this point.

Cucumber beetles are out feeding and bacterial wilt was reported in southern Ohio. Cucumber beetles thresholds are lower for younger plants because of the outsized risk of lethal infection. Seed treatments have been the go-to solution and they seem to be handling pressure well so far this season where they were used. Squash bugs have also emerged and are active. 

Bacterial wilt of cucurbits. Photo by Jim Jasinski, OSU Extension, Bugwood.org

 Flea beetles are feeding in cole crops. Imported cabbageworm and cabbage maggot feeding is severe in some brassica plantings. Heavy imported cabbageworm pressure has been observed in western Ohio.

Severely stunted growth can be an above-ground symptom of cabbage maggot root feeding. Photo by Chris Galbraith, OSU Extension. 

Severe Colorado potato beetle defoliation is being seen in eggplant and potatoes. Some growers have found extended protection using imidacloprid when planting seed pieces. Spinosad is another option in the arsenal, with the added benefit of being organic compliant.

Foliar diseases are being detected in high tunnel tomatoes. Many of these pathogens present on lower foliage first. At the time of fruit set, the lower ⅓ of leaves on tomato plants are generally not particularly productive from a photosynthesis standpoint, and therefore can be pruned to improve airflow between plants. Whitefly and aphid presence has been noted in peppers. Thrip pressure is heavy in onions in some areas.

As is the case every year, spray drift is being observed in vegetables. In some instances, symptoms resembling drift damage may occur on your vegetable crops when there is no obvious source of pesticides nearby. Drift particles may be moved surprisingly far by temperature inversions or other weather conditions. Other times, it may be an issue with herbicide residual activity in the soil.

One question from a community member: Is produce still safe to eat in cases where there is crop damage from pesticide drift? As is the case with most food safety questions – when in doubt, it’s best not to take the risk. There is uncertainty around how long it takes before residue levels are at or below the tolerance levels for situations in which a chemical is not registered for a specific crop. It is better to be on the side of caution when it comes to pesticides and produce safety.

Fruit

Fire blight incidence is high in some apple orchards. Apple scab is also being observed this year, with most infection occurring on fruit rather than foliage. Powdery mildew is being reported. Codling moth flights have been strong this season which is leaving growers with weekly sprays. Dogwood borer flights are particularly strong, and we do not have clear peaks this season. Some rosy and green apple aphids, as well as white apple leafhoppers, are being observed in orchards. 

Bacterial leaf spot is being reported on peaches. Peach leaf curl incidence is also high so far this season. Peach X-disease was recently confirmed by the OSU diagnostic lab. There is oriental fruit moth activity in some peach orchards but seems to be well controlled in most cases.

Foliar symptoms of peach leaf curl. Photo source: Nancy Gregory, University of Delaware, Bugwood.org

There have been calls about thrips and sap beetles in strawberries. 

Similar to vegetables, herbicide drift damage is popping up in vineyards and other fruit. For commercial growers who have experienced significant losses, reach out to ODA to report drift damage. For those wishing to pursue legal action – as soon as damage is observed, store damaged tissue in the freezer for preservation so that it can be tested at a later date.

For more information or if you have questions, please reach out to a member of the Fruit & Vegetable team or your county extension educator.

The Integrated Pest Management Program along with OSU Extension educators across the state are monitoring for five key pests this season. Monitoring sites are set up on farmer’s fields across the state and will be updated weekly.

Brown Marmorated Stink Bug – This insect will not be monitored for until late July though it is currently active in a broad range of specialty crops.

Spotted wing Drosophila – Two sites were set up this past week in Greene county. Several other county sites will be set up later this week. SWD detections will be reported next week.

European corn borer – Two sites were set up so far in South Charleston (Clark Co.) and Fremont (Sandusky Co.), both reporting 0 moths captured. Additional sites will start reporting next week.

Corn earworm – Four sites were set up so far in Clark, Sandusky, Fayette and Crawford counties. All sites reported capturing CEW moths except Sandusky County.

Squash vine borer – Five sites were currently set up in Clark, Greene, Ross, Seneca and Summit counties. All sites are reporting captures of SVB moths except for Seneca county.

Growers can access the monitoring data directly at this site.
https://docs.google.com/spreadsheets/d/1T4Uk8VKH-fY4qms4FlEwQvz8o1Lxk-t8LLHVz97kxNU/edit?usp=sharing