With the earliest signs of spring farmers can also begin to look for signs of cereal leaf beetles to start showing up in their wheat fields. CLB generally begins to come out of their winter habitations to colonize wheat fields in the first weeks of March. The adults do little to no damage to the wheat, themselves, but they lay eggs and it is the larvae that hatch that are the wheat pests that cause defoliation and wheat loss.
"We usually see peak egg hatch in the third week of April," says N.C. State University crop scientist Randy Weisz, "so if you are planning to make an insecticide application that gives you the best control of CLB, then usually the best time to apply that is sometime in April, to kill those larvae that are coming along."
However, Weisz says, an increasing number of growers are experimenting with tank-mixing a residual insecticide with the nitrogen applications they are currently putting on their wheat.
"That sometimes can work pretty well," he notes, "but the idea there is that you hope all the adults are finished colonizing the field before that insecticide wears out. If you are successful, if that happens, then you do don't have a CLB problem – and sometimes that works very well."
However, there are occasions it doesn't work out perfectly. Weisz notes his colleague, NCSU entomologist Dominic Reisig, has looked extensively at CLB management strategies on about 170 N.C. farms over the last two years, to determine what growers have been doing to control the pest and how efficiently what they did worked out for them.
Reisig reports he found about 7%-8% of the time when growers put their insecticide out with their N at this time of year (around early March) that the strategy failed. Weisz speculates the application was too early and the CLB adults kept coming into the field from over wintering sites.