WISCONSIN GROWERS first questioned the idea of a possible connection between potassium levels and soybean aphid populations in no-tilled bean fields. They wondered why they were often seeing a considerable variation in the aphid populations that were found in different areas within a single field.

As a result of the questions raised by farmers, University of Wisconsin entomologists have evaluated soybean fields throughout the Badger state and later followed up with several years of plot trials.

Aphid Threshold Timing.

Craig Grau says the researchers found that a soybean field with a low potassium level may reach the economic threshold for soybean aphid treatment with a needed insecticide considerably faster than a different area that enjoys higher fertility. “A field with higher potassium levels might take longer to reach that treatment threshold — or it might not reach it at all,” says the Wisconsin plant pathologist.

Among the reasons that soybean aphids tend to prefer plants that are stressed by potassium deficiency is that these plants contain a larger amount of amino acids. A number of research trials have shown that aphids require certain levels of a number of amino acids for optimal reproduction and growth.

Application Options.

While it appears that adding potassium may be a means of combating aphid concerns, no-tillers need to evaluate the most cost-effective way of getting this nutrient into the soil.

Iowa State University agronomist Antonio Mallarino has determined the most effective potassium application takes place with a 5- to 7-inch-deep band. While deep placement…