Crop & Pest Report


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Time to Scout for Soybean Aphids (06/30/16)

Over 100 soybean fields were surveyed by the IPM Survey scouts last two weeks in ND and MN (Source: P. Glogoza for MN).

Time to Scout for Soybean Aphids

Over 100 soybean fields were surveyed by the IPM Survey scouts last two weeks in ND and MN (Source: P. Glogoza for MN). Low numbers of soybean aphids were found in only one field in Sargent County in ND and one field in Isanti and Ottertail Counties in MN. The current temperatures in the high 70s to low 80s is favorable for soybean aphid development. So, now is a good time to start monitoring for soybean aphids.

Regular scouting (at least once a week) is important to determine which fields have economic population levels of soybean aphids. Fields near buckthorn, the overwintering host, may be colonized first and require earlier scouting. During mid-season, July and early August, infestations of soybean aphids in North Dakota have been strongly influenced by migrating aphids from soybeans south and east of ND. Inspect 10 plants and 4 sites per field for a total of 40 plants per field. Examine the entire plant, particularly new growth a top of plant. Use an action threshold of 250 aphids per plant if populations are actively increasing on 80% of the field for plants in late vegetative to R1 (beginning bloom) through the R5 (beginning seed) soybeans. ent.3 4

Avoid early-season application of insecticides for control of sub-economic populations of soybean aphids. Why? Here’s four good reasons to avoid spraying early:

1) Kills beneficial insects like lady beetles, lacewings, and nabids that keep aphid populations low and below economic threshold levels;

2) Increases secondary insect pest outbreaks, like spider mites. Early spraying of pyrethroid class of insecticides for soybean aphids can flare mite populations (except bifenthrin A.I.);

3) Requires second insecticide application (increasing input costs!) to control aphids and/or mites later in season since insect populations will rebound with aphid movements in area and aphid migrating on winds from other states; and

4) Increases the risk of aphids developing insecticide resistance due to unnecessary applications of insecticides. Unfortunately in SW MN, soybean aphids have developed resistance to a few of the common pyrethroids (e.g., Warrior and generics, etc.) that are used to control soybean aphids (Source: B. Potter and R. Koch. Univ. MN).


Janet J. Knodel

Extension Entomologist

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