Growers located in the upper Midwest, especially from the eastern Dakotas into Minnesota and Wisconsin, are encouraged to closely monitor soybean aphid populations over the next several weeks. Many fields are now in critical reproductive stages of growth, and soybean aphid populations are increasing to near treatable levels in some fields. It is recommended that growers check soybean fields through the R6.5 growth stage as any yield reductions directly related to soybean aphid damage occur on or before this stage of growth. University thresholds state that a field with at least a 250 aphid/plant average population in at least 80% of the field and a growing aphid population may be a suitable candidate for treatment (University of Minnesota). Additionally, it is important to watch the weather and not necessarily rely entirely on thresholds to determine if treatment is needed. If a field is nearing economic threshold levels, but a period of intense heat is expected for several days and/or a heavy rainfall event is imminent, it may not be wise to treat the field as aphid populations may decline due to the heat or excessive rainfall. On the other hand, if the weather forecast indicates several days of high temperatures in the 70s to low 80s and no rainfall, a proactive treatment approach may be warranted as soybean aphid populations can double in as little as a couple days under such conditions. It is also important to not rely on what your neighbor or the local coffee shop discussion is saying as soybean aphid populations can vary widely in adjacent fields. Scout your own fields and make any treatment decisions based on what is occurring in your fields and the weather forecast. Late or replanted soybean fields may be at a greater risk of seeing higher soybean aphid populations this growing season, as well, so these fields should be closely monitored until they advance past the R6.5 growth stage.
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Soybean aphids (SBA) are minute (less than 1/16th inch long), soft-bodied, pear-shaped insects.