What is in this article?:
- Sweep net is good tool for sampling kudzu bugs in soybeans
- Most fields infested at some level
• Entomologists are aware the sweep net “under-samples” nymphs compared to adults.
• The sweep net threshold, then, is calibrated for this under-sampling.
OLDER INSTAR kudzu bug nymphs in a Montgomery County, N.C., on June 9, 2013.
I’ve received many calls about the presence of nymphs in soybeans that are not being picked up in the sweep net.
This is not surprising, since populations of nymphs in nearby fields can be anywhere from mostly large to mostly small. Small nymphs are green, round, and are less likely to land in the net except in dense (read treatable!) populations.
Entomologists are aware the sweep net “under-samples” nymphs compared to adults. The sweep net threshold, then, is calibrated for this under-sampling.
You will begin to pick more nymphs up as they become larger. Moreover, there are some things you can do to improve your sampling technique for this insect (more on that below).
As an aside, if you have a field where you are going to apply a herbicide or fungicide and kudzu bugs are present at levels you think might hit one nymph per sweep in the future, you might want to tank-mix in the insecticide to eliminate the nymphs.
Keep in mind that small nymphs are not causing as much damage as large nymphs and the soybean plant has an amazing ability to compensate.
Kudzu bugs reduce the number of seed and seed size, but not pod numbers. Therefore, it might pay to wait and see what happens.
Also, remember that a spray at R2 or R3 will kill all beneficial insects, potentially flaring worm populations. Our first major corn earworm moth flight and egg lay into soybeans generally happens in the end of July/beginning of August.
It almost never pays to tank-mix an insecticide automatically hoping to kill pests that are there. You will kill what is there, but you will also set yourself up for future problems.
Full-season soybeans are all large enough to sweep for kudzu bugs. Double-cropped beans planted in stubble are difficult to sweep, but are not as attractive to kudzu bug as seedlings.
Sweeping is still an excellent technique to estimate the abundance of small nymphs, which blend in with soybean stems and are difficult to see. By the time nymphs are large enough to see up and down the stem, yield may already be compromised.