There are a number of things I would like to address with this article.
1.) Where we are in the life cycle and how this might impact your management efforts;
2.) Best known scouting procedures; and
3.) Why I do not think that treating soybeans with insecticides now will lower kudzu bug densities later in the field.
We have now reached the end of the first migration of adult kudzu bugs into soybeans. Keep in mind that these adults resulted from eggs laid last August (2012).
Adults can feed on the plants and cause stunting and/or yield loss. However, these insects are spent and will likely die out in the next few weeks. However, they might still lay some eggs in the meantime.
Soybean fields now need to be managed for nymphs hatching from eggs, rather than the adults migrating into the field (previous article listed recommended thresholds).
Focus on fields that had sub-threshold levels of adults that you might not have sprayed and fields where you might have sprayed the adults and had some re-invasion. Keep in mind there are two generations of kudzu bugs a year and that insecticides won’t kill the eggs.
If you are visually sampling seedling soybeans, peel back the plants to reveal the stems. Some plants will be very heavily colonized, with other plants relatively clean (we think the insect has an aggregation pheromone, making it attractive to other kudzu bugs).
Base treatments decisions on a per-plant average. My best guess is that neighboring plants will compensate for any stunting that might occur on heavily infested plants.
Some full-season beans are now “sweepable”. I recommend using the sweep net whenever you can and following the one nymph per sweep threshold anytime your beans are near reproductive stages.
Small nymphs are very difficult to see, as they blend in with a soybean stem. By the time nymphs are large enough to see stacked up and down the stem you have probably already lost some yield.
Kudzu bugs take a long time to develop relative to other insects, so this will not happen overnight. Entomologists are aware that the sweep net “under-samples” nymphs compared to adults. Our sweep net thresholds are calibrated for this under-sampling.
For both visual samples and sweeping, you can check field edges to see if the bugs are present. However, this, insect congregates much more heavily on these edges. You must base all treatment decisions on field interiors. Start sampling at least 50 feet into the field to make any treatment decisions, being sure to visit several parts of the field.
This is speculation, but I do not think it is a good idea to treat soybeans now, hoping we can reduce their abundance later in the season. This insect has been sprayed like crazy in Georgia and South Carolina, but is still showing up in great numbers.
Also, we know for certain that many individuals can be produced on kudzu and suspect it can reproduce on wisteria.
My opinion is that there are enough wild reproductive hosts to create a source of insects for soybeans anywhere in the state.
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