What is in this article?:
- Itâ€™s time to scout soybeans for insect problems
- Problem near field edges
• Insects of particular note to watch for are three-cornered alfalfa hopper and kudzu bug.
Problem near field edges
Grasshoppers are generally more of a problem near field edges and if a treatment is applied, sometimes a border treatment can be effective. Adult insects are difficult to kill and pyrethroids or acephate (Orthene) are equally effective. Nymphs can be killed with Dimilin.
Cutworms have not been an issue this year, but will feed at night and are difficult to find. You might suspect cutworms are a problem based on their feeding habit of cleanly clipping plants. They rarely are an economic problem, but are more of an issue in no-till fields.
Fortunately the threshold for foliar-feeding pests of soybeans is easy — 30 percent defoliation throughout the entire canopy up to two weeks before blooming.
Pests to watch for this time of year are bean leaf beetle, southern corn rootworm, and various caterpillars. As of this time, I have not heard of a treatable situation for any foliar-feeding pest of soybeans in 2012.
Suckers and girdlers
Three-cornered alfalfa hopper has been a recent problem in Mississippi cotton and Mississippi and Tennessee soybeans.
Last year, they caused lodging issues in the North Carolina Piedmont from girdling done during the early season (see previous blog post for description of injury).
Unfortunately, once you notice the girdling on the plant — generally later in the season — the damage has been done. Now is the time to scout for these insects in soybeans.
Although sampling beans with a sweep net is difficult early in the season, do your best to sweep the foliage.
The treatment threshold for three-cornered alfalfa hopper is one per sweep in beans less than 10 inches tall. Pyrethroids do a fair job of managing this insect, with bifenthrin looking a little better than most.
Kudzu bug is widely distributed across the state, albeit generally in low abundances on soybeans.
There have been a few cases where treatments have been made. These were very early planted soybeans that were an early maturing variety (Group IVs).