Sometimes you just have to start digging to find out what’s going on in the field. While western corn rootworms haven’t disappeared on the insect pest radar, they have certainly been less troublesome with the widespread use of stacked Bt hybrids. Is that changing?
A general observation shared by Midwest entomologists is that there has been lower density of several insect pests, including western corn rootworms, over the past several years. In 2011, corn rootworm egg hatch was delayed because of cool soil temperatures. However, recently reports of root pruning have been coming from some areas of Iowa and Illinois.
To get a first hand look, I headed to the field last Friday, July 29, with Dave Shenaut, Monsanto Technology Development Representative. His plots on the Parkland College campus, Champaign, Ill., gave us a good chance to compare the feeding on roots that had been inoculated with rootworm larvae to infestations that occurred naturally. We found natural infestations of rootworms had done nearly as much damage as where the corn had been inoculated.
“Rootworms are still here. Growers thinking they may not need the technology, may want to reassess,” says Shenaut.
He recommends that growers dig roots and look for injury. Non-Bt fields are most susceptible to larval damage. Continuous Bt corn fields with previous damage are good candidates for scouting too. Sample corn plants in different areas of the field to estimate infestation levels. A power washer may be needed to wash off roots for a good clean look.
Listen in I visit with Shenaut on the Parkland College campus: