Classic Herbicide Update

What effect does Classic use have on spotted wilt and peanut yields, and should you still use it?

By Dr. Eric Prostko, Extension Weed Specialist, University of Georgia

Classic was first registered for use in peanuts in 1989. Currently, 10 to 20 percent of the peanut acres in Georgia are treated with this herbicide for late-season control of Florida beggarweed. Some evidence has suggested that Classic applications may have an influence on the expression of tomato spotted wilt virus (TSWV).

From 2000 to 2007, my colleagues and I conducted 15 field trials with six different peanut varieties to investigate this issue. The varieties were as follows: Georgia Green, AP-3, C-99R, AT-201, GA-02C, GA-03L.

The following are questions we wanted to answer through this research and what we determined.

Do peanut varieties respond differently to Classic?
Our research indicated that there was no interaction between peanut variety and Classic.

Do Classic applications result in an increased expression of tomato spotted wilt virus?
Our results indicated that when Classic is applied between 60 and 99 days after emergence (DAE), significant increases in spotted wilt, up to 9 percent, can be expected (see chart at top right).

Do Classic applications reduce peanut yields?
When averaged over six peanut varieties and 15 locations, we were unable to prove that Classic caused significant yield reductions (see chart above).

Should a peanut grower use Classic?
Based upon the research data presented above, I would recommend that peanut growers use Classic for the control of late-season Florida beggarweed when the populations of this weed are dense enough to impede digging or harvesting and/or reduce the deposition of fungicide sprays. PG