Rootworm power trip

Corn rootworm is known in some circles as the “billion-dollar bug” because estimates of its damage approach $1 billion per year. University of Illinois research shows yield losses of 15% for every node of roots destroyed, and up to 40% loss from rootworm
in drought conditions.

That’s why Bt rootworm hybrids were so eagerly adopted across the Corn Belt. However, the Cry3Bb1 gene that confers rootworm resistance in some hybrids has suffered greater-than-expected losses in some areas. In those situations, Monsanto recommends using pyramided products (like SmartStax) that contain multiple corn rootworm traits or use a soil-applied insecticide at planting.

Remember to scout for adult rootworm beetles at tassel. More than five beetles per plant clipping silks can lead to yield loss significant enough to warrant an insecticide spray. Researchers at Purdue University say a threshold above just one beetle per plant may even be warranted in a corn-on-corn program to protect the following year’s crop from
a big hatch of larvae.

Watch cutworms

Unlike most infestations of corn rootworm, which thrive in continuous corn, black cutworm tends to be a bigger problem in first-year corn, according to Mike Gray, Extension entomologist at the University of Illinois.

Weedy or late-planted fields tend to attract cutworm moths, which swoop in to lay eggs. An individual larva can cut three to four plants in its lifetime, and heavy infestations can be devastating.