By: Clint Schroeder
The 2019 growing season continues to present new challenges for Ohio farmers. The late planting coupled with localized extreme weather events has changed the way we need to think about scouting for disease and pest issues in our crops. The good news is that the late planting will delay the corn crop enough that we should not have to worry about Japanese Beetles feeding on corn silks at pollination time. The bad news is that we have had more time for spore counts to build up for foliar diseases like gray leaf spot, northern corn leaf blight, and common southern rust. In a normal year we would look for disease pressure around tasseling, but this year we could start to see infection at the V8-V12 growth stages. If the hybrid is susceptible and conditions become favorable, high levels of infection at V8-V12 will result in greater and more rapid diseases development, and consequently, greater damage to the upper leaves before grain-fill is complete. Research by OSU Extension since 2010 has shown that the ideal time to treat with a fungicide is at the VT/R1 even if there is presence of disease prior to that stage. Growers also need to be aware that there is a new foliar disease that showed up in Northwest Ohio in 2018. Tar spot is more likely to show up in no-till fields and can be identified by the raised circular black lesions.
It’s also time to scout for western bean cutworm (WBC) egg masses. I am currently monitoring two traps in Allen County and reporting those numbers to our state office. Last week there was an average of 7 moths in the traps locally, but the state average was 25.3 moths per trap. It will be interesting to see if the numbers continue to rise or if we taper off similar to 2018. WBC egg groups are often found on the upper leaf surfaces in clusters. The eggs are round and first appear white, then gradually turn a dark purple. Once eggs turn purple, they will hatch within 24 to 48 hours. If infestations exceed the threshold level, over 8% of plants having eggs or larvae, many insecticides are available to treat with. However, as with any ear-burrowing caterpillar pest, timing is critical. Insecticide applications must occur after egg hatch, or after tassel emergence, but before caterpillars enter the ear. If eggs have hatched, applications should be made after 95% of the field has tassel. If eggs have not hatched, monitor for the color change. To search for larval injury after it has occurred, search the corn for ears having feeding holes on the outside of the husks.
Average western bean cutworm (WBC) per trap in monitoring counties in Ohio for 2016 (blue), 2017 (red), 2018 (green) and 2019 (purple).
In soybeans we need to be scouting for insect pressure. We’ve had a lot of Japanese Beetles present this year and they will do damage by eating the foliage of bean plants. As a general rule of thumb treatments are warranted when defoliation exceeds: 40% prior to bloom, 15% from bloom to pod-fill, and 25% after pod-fill to plant yellowing. Another pest that we need to be looking for is the brown marmorated stink bug. Adults are speckled brown-gray with a white band on its antennae. There are dark and white bands around the edges of the abdomen, with the whitish markings appearing as triangles. Early nymphs have a dark head with an abdomen that is orange and red with black stripes down the middle. Later nymphs are brown with a white band on its antennae and strong white bands on its legs. The underside of the nymphs is characteristically white.
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| Adult brown marmorated stink bug. | Brown marmorated stink bug nymph. |
These bugs will damage soybeans by puncturing tissues with their piercing and sucking mouthparts, and then extracting plant fluids. They prefer to feed on the young pods and developing seed within. This can cause significant yield loss as the seed will become shriveled and deformed. Scouting for this pest should ramp up as soybeans begin to flower. Given the late planting we have experienced it might be possible that the insect pressure will require multiple insecticide treatments to protect yield potential.
For more information on these pests or any other things you might be seeing this year please contact us at 419-879-9108. I know in these conditions it is often times frustrating trying to decide on treatments for a crop that doesn’t have great yield potential. I’d be more than happy to come out and talk about the threshold levels OSU Extension has set for treatments and the economics behind that. It is also important to remember that we need to be using our insecticides and fungicides responsibly to prevent not only resistance, but also negative public sentiment.