March 14, 2016

Chemical Reregistration: Leaf Lettuces Get “New” Crop Protection Tool

With Western Growers’ help, Kerb SC Herbicide is now, once again, federally registered for use on leaf lettuces, and labels are available in both California and Arizona.  The availability of this key crop protection materials is being lauded by the manufacturer—Dow AgroSciences—as well as by the grower community.

“Western Growers has been working to make this use available for several years and we are extremely pleased that that U.S. Environmental Protection Agency and the states have restored leaf lettuce to the Kerb label,” said Hank Giclas, Western Growers senior vice president of science & technology and strategic planning.

“This is an incredibly important new label for leaf lettuce growers,” said Jesse Richardson, Dow AgroSciences field scientist for Southern California and Arizona.  “No other herbicide controls as many weeds in lettuce as Kerb.  Kerb has been the standard for efficacy for decades.  Lettuce growers typically grow both leaf and head lettuce, so this will allow them to use Kerb across all lettuce acres.”

Though this does represent a new label for leaf lettuce growers, in reality it is a return to a tried and true crop protection tool.  Kerb SC was first registered in California in 2008.  At that time, “lettuce” was not differentiated as head vs. leaf by the U.S. Environmental Protection Agency.  Due to a federal change in tolerance expression in 2009, head lettuce, endive, escarole and radicchio greens were labeled for use but leaf lettuce was no longer covered.

Since that time, Dow AgroSciences (DAS) and the IR-4 Program have worked tirelessly to develop the data necessary to support the addition of leaf lettuce.  “We conducted state-of-the-art toxicology research that resulted in cancer reclassification to ‘Not Likely to be Carcinogenic to Humans,’ performed an innovative series of residue trials that now allow 25-35 day pre-harvest intervals at lower use rates for baby greens and did a complete overhaul of the risk assessment to incorporate the above changes,” said Richardson.

The association played a large role in demonstrating the importance of this product and its usefulness to the lettuce and leafy greens industry.  “Western Growers helped document a critical need and facilitated direct dialogue between industry, USEPA and state agencies which was instrumental in this approval,” said Brian Bret, regulatory manager for Dow AgroSciences.

Jim Mueller, Dow AgroSciences field scientist for Northern California, said several groups offered strong advocacy for the re-registration effort including Western Growers, California Leafy Greens Research Board, University of California, Yuma Fresh Vegetable Association, University of Arizona, and USDA-ARS.

A ‘split shot’ supplemental label was issued in 2012, allowing split applications of Kerb on head lettuce.  That label will now apply to leaf lettuce as well.  Dow AgroSciences also reformulated Kerb in 2012, switching from water soluble packets to a suspension concentrate.  The new formulation makes applications and mixing easier, and is the preferred formulation in the produce industry.

Giclas said the new label for Kerb SC includes a prior supplemental label for chemigation at lower rates to facilitate shorter intervals between spraying and harvesting, which was first supported by Western Growers through a special local needs label in 2005.