Response of Soybean Insects to an Autumn-Seeded Rye Cover Crop

We evaluated the hypothesis that the use of an autumn-seeded winter rye, Secale cereale L., cover crop in soybean, Glycine max (L.) Merr., could lead to decreased insect pest pressure. We compared insect pest and natural enemy populations in an organic soybean production system with soybeans planted into an autumn-seeded rye cover crop (i.e., soybeans planted in spring into a rye cover crop that had been planted the previous autumn). Small-plot experiments were conducted at two locations in southwestern Minnesota to compare insect populations on soybean planted into fallow ground versus soybean planted into rye that was managed by mowing using three different techniques. Densities of potato leafhopper, Empoasca fabae (Harris), were significantly lower on soybean in all of the rye treatments compared with soybean without rye at both locations. Densities of soybean aphid, Aphis glycines Matsumura, were significantly lower on all of the treatments incorporating rye than the soybean-only treatment at one site, but the suppressive effect of rye depended on the specifics of rye planting at the other site. Densities of bean leaf beetle, Cerotoma trifurcata (Forster), were significantly lower in the rye plots than soybean-only plots at one of the two sites. Foliar-foraging insect predator densities did not differ significantly among treatments at either site. Soybean yields did not differ significantly among treatments at either location although there was a trend for lower yield in two of the rye treatments. A statewide survey also was conducted to compare A. glycines infestations in Minnesota soybean fields with and without a rye cover crop. The proportion of plants infested and infestation ratings were both significantly lower in soybean fields with rye than in those without.