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Insects in- Soybean
By David G. Hallauer District Extension Agent Crops & Soils/Horticulture Soybean aphids have again arrived in Kansas. They were discovered on July 12 in a soybean rust/Soybean aphid sentinel plot in Lyon County. They have also been detected in Riley County. This is a little earlier than in past years. Interestingly, this is approximately the same time frame as in 2005 and populations that year never really became troublesome. What can you expect? Soybean aphid populations seem to be sensitive to hot temperatures, specifically temperatures over 95 degrees Fahrenheit. Hot summer temperatures may not actually kill the aphids but it does seem to drastically reduce their ability to reproduce. If they are not rapidly reproducing this gives some of their natural enemies, i.e. predators and parasites, the opportunity to help regulate the aphid populations. Aphid populations can increase very quickly. Soybean aphids are relatively small, light green aphids with the distinctive black cornicles or "tail pipes" at the tip of the abdomen. Infestations usually start at the outer canopy on the newer leaves. This aphid can transmit many viral diseases but can also stress plants and reduce yields by virtue of their feeding which removes nutrients from the plant. While aphid populations discovered so far are small and widely scattered, with the late development of the soybean crop this year, that could spell some cause for concern. soybeans in the late vegetative and early reproductive stages are probably the most susceptible to aphid feeding, right where we are now. Economic thresholds for Soybean aphids, from states that have had annual problems, is around 50 per plant in pre-reproductive plants and approximately 250 aphids per plant in R1 (beginning bloom) to R4 (full pod). This takes into account a seven-day lead time between scouting and treatment to make arrangements for treating. For information about treatment thresholds, sampling and a new technique of "speed scouting, and insecticides registered for use against Soybean aphids, drop me a line. We are trying to track populations so I would appreciate knowing if you have an infestation and what you may be planning to do about it. Dectes soybean stem borer adults have also emerged and were founds last week in soybean fields in north central Kansas. Not a common pest but one that can cause some damage if it gains a foothold. Potato leafhopper damage has also been reported on soybeans. Again, they aren´t a common problem on soybeans, but with the numbers we´ve seen on alfalfa this year, it wouldn´t be surprising to find them on soybean. Generally, they aren´t a big problem, but they are worth watching. Insects on: Alfalfa Potato leafhopper populations are still causing damage across North Central and Northeast Kansas. These little pests will be with us for another 6 or more weeks. If you swath your fields instead of spraying, you still need to make sure you monitor the stubble as there may be eggs in the remaining stems or enough hoppers remaining to retard regrowth. Date: 8/2/07
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