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Pests, pests & more pests
Big weed year
This year left no shortage of insects attacking crops in Missouri. This summer, University of Missouri (MU) scientists at a July field day discussed some of the insect challenges this year at the MU Bradford Research and Extension Center near Columbia.
City slicker insects
Ever experienced new folks who move into the neighborhood and immediately become pests? That’s the case with Japanese beetles. “They used to be concentrated in suburban areas like Kansas City and St. Louis,” says Wayne Bailey, University of Missouri Extension entomologist. Japanese beetles have since moved into rural areas. This year’s wet weather favored high grub populations that later surfaced as Japanese beetles.
High Japanese beetle populations can curtail corn and soybean yields. In corn, beetles that clip silks can adversely impact pollination. Meanwhile, beetles that chew on soybean leaves can slow plants’ photosynthesis. In Missouri, insecticide treatment is recommended on corn when 4 or more beetles are present and if pollination is less than 50% complete. In soybeans, pesticide treatment is recommended when Japanese beetles defoliate plants by 20% to 30%.
A downside to an upside
When warranted, fungicides do a good job controlling fungal disease in row crops. The downside, though, is fungicides can kill off some good fungi, too. This has spurred appearances of green cloverworm and fall armyworm in row crops. “By applying fungicide, it kills the natural fungi that kill green cloverworm,” says Bailey. “It’s the same thing with fall armyworm.” When warranted, insecticides can control these pests. However, unnecessary fungicide applications can kill fungi that infect and kill green cloverworm and fall armyworm for free, says Bailey.
Corn earworm makes a move
A third pest in this trio, corn earworm, is also exhibiting different behavior than in the past. The good news? Infestations in corn like the one you see are down, due to traited hybrids. The bad news is corn earworm is popping up in soybeans. “They’re a pod feeder,” says Bailey. “One corn earworm larvae per plant can strip a plant.” Late planted or double-crop soybeans are most vulnerable to corn earworm attack. Insecticide treatment is recommended when 20% or more defoliation occurs during pod fill, if one or more larvae are present per linear foot of row or if it damages 5% to 10% or more of soybean pods.
Red-banded stink bug
There could be a big stink coming from the red-banded stink bug.
“Right now, it is in two southern counties in Missouri, coming out of Louisiana and other southern states,” says Bailey. In Louisiana, the red-banded stink bug has sliced soybean yields from 60 bushel per acre down to 21. “It can displace other stink bugs,” says Bailey. “It is more aggressive, and it can withstand more chemicals than other stink bugs.” On the other hand, colder climates may slow or restrict the pest’s movement northward. MU entomologists are monitoring its movement in Missouri.
Soybean stem borer
Soybean stem borer, a pest that tunnels into soybean plants, is surfacing several southeast Missouri counties. Some fields have 85% plants infested. So far, though, it’s unclear how to treat them, or just how adversely they impact plants. Insecticides can kill adult beetles. However, more beetles move back into the field the following day. Instead, cultural practices, such as controlling weed hosts like cocklebur and giant ragweed, and harvesting the crop as soon as it matures can help slice losses from lodged plants.
Field day focuses on Japanese beetles, corn earworm & a new stink bug.