“Scouting for insects in soybeans at this time of year can be quick and painless,” said Jake Hansen, Federated agronomy sales rep in Rush City, but he added, “depending on what you find!” Spider mites and soybean aphids are the two most yield-affecting pests in the Federated areas.
Scouting for spider mites , as small as they are, can be somewhat difficult. “Most times we don't catch them until damage symptoms show up in the crop,” said Hansen. Spider mite damage looks like mild to severe burning, and the beans will turn almost brown.
Watch the weather . . . because the best way to monitor spider mites and prevent crop damage is to monitor the weather, Hansen noted. “Spider mites really thrive in hot, dry weather.” If the weather sets up for a dry spell, keep checking for spider mites. Hansen ventured that “all bets are off for mites this year, but we still have a few weeks left in July and early August for them to show up.”
Keep watch for soybean aphids (pictured above) too, which are much easier to locate by eye when scouting fields. Hansen said, “When heavy pressure is present in a field, you can see yellowing in areas of the field.”
To scout for aphids, look at the new growth and carefully check the uppermost leaves of the plant. Aphids tend to congregate on the underside of the leaf, out of the sun. Look for their distinct shape with small, black cornicles that look like antennae on their hind ends – and they move very slowly. Some aphids have wings, others don’t.
When to treat: The threshold to look for with aphids before considering treatment can be from 200-250 aphids per plant, and is dependent on crop stage and commodity price. Hansen said, “If your count is 150 or above per plant, treatment should be considered because aphids can reproduce rapidly.”
Another factor to consider is the presence of natural predators to aphids. Kevin Carlson, Federated’s senior agronomist, reported late last week that evidence of predators was good. He said, “We’ve been seeing a few aphids, but we are also seeing predators (photo below), which is great. We’re seeing both Asian beetles and parasitic wasps.” Pirate bugs are another predator of aphids.
“However,” said Hansen, “due to the aphid's strong reproduction cycle, common predators to aphids may only depress the population slightly,” so don’t assume all is well. Keep a close eye on the aphid infestation and plan to treat as needed. Talk to your Federated Agronomist about the best treatment options for your farm.