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Soybean Aphids

Jul 31, 2020

Soybean Aphids:

As we approach August, I think of the old saying that August makes soybeans. Most of our soybean crops are putting on pods and finally starting to fill those pods with nutrients and sugars. However there is one last controllable pest that becomes a problem many years around this time period. Soybean aphids. Soybean aphids are a small insect with a piercing/sucking mouth part that acts like a straw for the insect. The aphid will stick its “straw” into the soybean and continually suck nutrients and sugars out of the plant. One aphid is not the problem though, it is when you have many. In fact the sprayable threshold for aphids is 250 aphids/plant. With this nice weather we are having now, that number can be achieved quite rapidly. The University will say under ideal conditions aphid populations can DOUBLE every 3 days. This is a trend that the aphids are now following. Many of the fields I scouted last week burst from 20-30 per plant last week to now 80-100 aphids per plant this week. Many of these field will get sprayed next week.

With aphids we also want to consider the beneficial insects in the field. These include lady bugs and their larvae (see picture), lacewings, and many other insects. These insects can actually help to keep populations of aphids from rising too quickly. Some years we have to spray for aphids twice and this is largely due to the fact that when we spray for aphids we typically kill the good insects in the field too. However, we can avoid killing those insects now with the product called Sefina. Sefina is a insecticide that only targets piercing/sucking insects. It will not kill ladybugs, bees, or any other insect that might be in the soybean field. This product only targets soybean aphids in your field. If you have a population of beneficial insects in your field, consider spraying Sefina for the aphids to avoid a costly 2nd application later on.

Talk to your agronomist for more information regarding soybean aphids and what products to use to control them.

Jackson Gregory
Belgrade Cooperative Agronomist

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