Increased Risk of Insect Injury to Corn Following Rye Cover Crop.

Decreased pest pressure is sometimes associated with more diverse agroecosystems, including the addition of a rye cover crop (Secale cereale L.). However, not all pests respond similarly to greater vegetational diversity. Polyphagous pests, such as true armyworm (Mythimna unipuncta Haworth), black cutworm (Agrotis ipsilon Hufnagel), and common stalk borer (Papaipema nebris Guenee), whose host range includes rye have the potential to cause injury to crops following a rye cover crop. The objectives of this study were to compare the abundance of early-season insect pests and injury to corn (Zea mays L.) from fields with and without a rye cover crop on commercial farms. Fields were sampled weekly to quantify adult and larval pests and feeding injury to corn plants from mid-April until corn reached V8 stage, during 2014 and 2015. Measurements within fields were collected along transects that extended perpendicularly from field edges into the interior of cornfields. Adult true armyworm and adult black cutworm were captured around all cornfields, but most lepidopteran larvae captured within cornfields were true armyworm and common stalk borer. Cornfields with a rye cover crop had significantly greater abundance of true armyworm and greater proportion of injured corn. Both true armyworm abundance and feeding injury were significantly greater in the interior of cornfields with rye. Common stalk borer abundance did not differ between cornfields with or without rye cover. Farmers planting corn following a rye cover crop should be aware of the potential for increased presence of true armyworm and for greater injury to corn.