Integrated Crop Management News

Corn rootworm egg hatch in Iowa typically occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. Development is driven by soil temperature and measured by growing degree days (GDDs). Research suggests about 50% of egg hatch occurs between 684-767 accumulated GDDs (since January 1; base 52°F, soil). Most areas within Iowa have reached peak egg hatch for corn rootworm (Figure 1), and we have heard several reports of folks finding larvae by digging roots in cornfields.

Plant-parasitic nematodes that feed on corn are relatively common in Iowa, but their presence in fields does not mean that damage and yield loss are occurring. The number of nematodes necessary to damage corn varies greatly among different nematode species, and the potential for yield loss can only be assessed by determining the types and numbers of nematodes present in a field. This article explains how to sample corn fields to determine if nematodes are causing damage and likely to reduce corn yields. Management options for nematodes on corn also are listed in the article.

Most soybean producers in Iowa have heard of the soybean cyst nematode (SCN) and are aware it is considered the most yield-reducing soybean pathogen in Iowa. Adult females of SCN can be seen on infected soybean roots with the unaided eye and they now are present on soybean roots. Read more in this article about digging roots to check for SCN.

Stalk borer is an occasional pest of corn, but it can be persistent in some fields, especially those fields near perennial grasses that serve as overwintering sites (fence rows, terraces, and waterways are typical sources). Tracking degree days is a useful way to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications are only effective when larvae are migrating and exposed to the insecticide. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated.