Louisiana Hits Record Levels Of Bollworm Pyrethroid Tolerance For July

Louisiana State University this week released the charts showing how bollworm (corn earworm) pyrethroid tolerance compared in July to the same month going back to 1988. This particular chart tracks the lesser dose used in vial testing of moths.



Survivorship for both vial rates increased about 10% compared to 2009, according to a report issued in this week's Louisiana Crops Newsletter.

"This also represents the first time that survival has been measured above 50% for a monthly summary since testing was initiated during the mid-1980s," according to the report. "Bollworm tolerance to pyrethroids and high pressure within fields could lead to control problems in fields treated with a pyrethroid insecticide alone."

And, in fact, those kinds of control failures have been widely reported this season in both the Delta states and the Southeast.

"Pyrethroid insecticides should not be used alone at this time when bollworms are the target pest of an insecticide application," the report stressed. "When attempting to control this pest in cotton and soybeans, pyrethroids should be co-applied with Orthene (acephate) or other OPs to provide an additional mode of action and reduce the probability of field control failures."

Bollworm populations have increased, overall, in many Louisiana cotton and soybean fields, the report also noted. "The July moth trap captures from around the state are higher than that observed in previous years. These populations are the result of the generations that developed in Louisiana corn fields, but also migrated into the state from Texas."

The report was issued by Joshua Temple, Steve Micinski and Roger Leonard, LSU entomologists.

- Owen Taylor