Crop & Pest Report

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No Soybean Aphids (08/15/19)

The most common insect pest problems in soybeans reported the last couple of weeks were some remaining pockets of thistle caterpillars and grasshoppers (nymphs and adults) causing leaf defoliation during flower to pod development. The Economic Threshold (E.T.) is 20% defoliation for all foliage-feeding caterpillars.

The most common insect pest problems in soybeans reported the last couple of weeks were some remaining pockets of thistle caterpillars and grasshoppers (nymphs and adults) causing leaf defoliation during flower to pod development. The Economic Threshold (E.T.) is 20% defoliation for all foliage-feeding caterpillars. The E.T. for grasshoppers uses a count per square yard: 8-14 adults per square yard in field and 30-45 nymphs per square yard in field. No soybean aphids were reported.

Although increasing population of soybean aphids are being observed in southeastern MN, soybean aphid counts continue to be zero to very low in ND. Besides the late start to soybean aphids this year, the recent weather conditions are just not suitable for fast reproduction (78-83F, moderate humidity are optimal). The IPM Crop Scouts observed 0-14% of plants in field infested and an average of <0.1 aphid per plant in ND (see map below). About 93 percent of the fields scouted had no soybean aphids present in ND. The pie chart map shows the proportion of plants observed by different aphid densities. If the pie chart shows mainly orange to red, this indicates those fields have more plants that are getting closer to the economic threshold of 250 aphid per plant. Maps are posted weekly on the NDSU IPM website.

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Janet J. Knodel

Extension Entomologist

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