Tuesday, September 8, 2009

Soybean Aphid & Other Insects in Double-Crop Soybeans

I have received several reports and questions from Extension agents, consultants and company reps concerning near economic threshold populations of Soybean Aphid (SA). Fortunately, all of these fields so far are in R6 or later stages. However, in addition a number of these reports included the observation that there are many other fields that are still in the R3 to R5 stages. These earlier stage plants will remain at risk to SA until they reach the R6 growth stage. These are the fields in which you should spend your scouting time.

The SA economic threshold is 250 aphids per plant, on 80% of the plants, with an increasing population. This threshold holds through plant stage R5. For more mature plants a great many more aphids per plant would be required to provide a benefit for an insecticide application. The exact number is currently under investigation but it is likely at least 500 aphids per plant and may well be 1000 aphids per plant.

In addition there have been scattered questions concerning stinkbugs and bean leaf beetles. Both of these insects are still present and will be feeding directly on the pods. At least one report I have seen, contains stinkbug numbers much greater than the threshold and bean leaf beetle populations very near thresholds. Both of these insects bear close observation as beans progress to maturity.

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