Since its first detection in the U.S. over a decade ago, soybean aphid continues to be a yield limiting threat to soybean production in South Dakota.   Aphids can be managed effectively with insecticides through field-scouting and the use of economic thresholds.  An exciting new option for the management of soybean aphids is soybean varieties with bred-in resistance.  These resistant varieties provide new ammunition against this yield-robbing pest.

Growers selecting soybean seed for the 2012 growing season may expect to see high-yielding varieties with the Rag1 gene in the market. Field studies in South Dakota and other soybean-producing states show slower population development of soybean aphids on varieties that have the Rag1 gene.  Often aphid populations on Rag1 resistant varieties are as low as 10% of populations on susceptible varieties. They may not need to be insecticide treated in many situations.  However, it is important to note that under heavy aphid pressure these varieties can still reach economically damaging levels. Thus, field scouting to determine the need of chemical control is still necessary on these soybean varieties which contain the Rag1 gene.

To complicate the matter, research has shown that soybean aphid populations can vary in terms of their relationships with the Rag1 gene. There are at least three different soybean aphid biotypes in the United States. Soybean varieties with Rag1 gene can effectively slow down the development of aphid population from biotype 1. On the other hand, the population development of aphids from biotypes 2 and 3 are not inhibited by the Rag1 gene. The specific soybean aphid biotype or mixture of biotypes in South Dakota is not yet clearly identified.

Other resistance genes against soybean aphid, for example Rag2, -3 and -4, are currently on the breeding pipelines for incorporation into elite varieties.

Further online information:
Soybean Aphids in South Dakota
Soybean aphid article at the Northern Plains IPM Guide