Western and northern corn rootworm are major corn pests in Iowa and surrounding states (Photos 1 and 2). Farmers have seen several management changes, including the release of four Bt-rootworm traits to suppress corn rootworm larvae since 2003. Although both species are persistent pests, western corn rootworm is particularly adaptable. The Gassmann Lab at Iowa State University (ISU) has demonstrated western corn rootworm resistance to all Bt rootworm traits in Iowa.
Integrated Crop Management News
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Every year we evaluate commercial fungicides on corn applied at V5 alone, VT-R1 alone, or both growth stages for disease control and effect on yield. The trial was done in collaboration with the farm managers at four Iowa State University (ISU) Research and Demonstration Farms (Table 1). The trials are laid out in a randomized complete block design with four to six replicates. Plot sizes are 10 foot (4 rows) wide and 30-100 foot long. Hybrids varied by location.
Tracking degree days is a useful tool to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar applications, if needed, are only effective when larvae are migrating and exposed. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated. Southern Iowa counties reached this important temperature benchmark over the holiday weekend (Fig. 1), and therefore scouting for migrating larvae should begin now to make timely treatment decisions.
Aphids are common insects to see in field crops, especially in alfalfa. In Iowa, there are at least four aphid species that can persist on alfalfa. A recent report of pea aphids near Clarion, IA from field agronomist Angie Rieck-Hinz prompted me to write this article. Learning to distinguish aphids in alfalfa takes a little practice, but is worth knowing for making sound treatment decisions.
The regional Corn Nitrogen Rate Calculator (CNRC) website was recently updated with a fresh look and a revised N response trial database. The concept and calculation process remains the same. The CNRC website url has changed to (http://cnrc.agron.iastate.edu/). The site is now more user friendly on smartphones.
Seedling diseases could be an obstacle for farmers this year with the early planting of corn and soybean. While we all hope that seedling diseases will be a small consideration, it is important to be ready for them. It is also important to know how to sample for them.
The black cutworm (BCW) is a migratory pest that cuts and feeds on early vegetative-stage corn. Black cutworm moths arrive in Iowa with spring storms each year. These moths lay eggs in and around fields and the emerging BCW larvae cut seedling corn. The sporadic nature of this pest makes scouting essential to determine if management is needed. Scouting for BCW larvae helps to determine if an insecticide application will be cost effective.
A simple but potentially valuable spring task to consider is sampling fields for the soybean cyst nematode. And since we are heading into the cropping season, it makes sense that attention be given to those fields in which soybeans will be grown in 2016.
Seedcorn maggot is a seed and seedling pest of corn and soybean. Plant injury is especially prevalent during cool and wet springs. The larvae, or maggots, feed on germinating corn and soybean seeds or seedlings (Photo 1). They can feed on the embryo, delay development or kill the plant. Infestations tend to be field-wide instead of grouped together like for many other pests. To confirm seedcorn maggot injury, check field areas with stand loss and look for maggots, pupae and damaged seeds (e.g., hollowed out seeds or poorly developing seedlings).