Herbicide Registrations for Different Types of Lettuce (August 19, 2015)

Herbicide registrations were always the same for all types of lettuce until 2009 when this changed. Prior to around 1920 there was very little lettuce produced in this part of the country and what was produced was mostly leaf or butter types. After 1920 this changed dramatically. Lettuce acreage became increasingly important in the west after 1920 when the acreage increased and the type of lettuce produced changed from leaf to iceberg. The shift to iceberg was largely because iceberg shipped long distances better than other types. In the early years, lettuce was packed in sheds, placed in crates and cooled with ice. More than 80% of the lettuce produced in this region was iceberg when the first herbicides were registered for use on it. The data collected to support herbicide registrations were done largely with iceberg lettuce and only “lettuce” appeared on the labels. Vacuum cooling was adopted in the 1950’s and the types of lettuce produced here have shifted over the last 20 years. Now almost 50% of the acreage is leaf types (including romaine). The most broad-spectrum of the limited herbicides registered for use on lettuce is Pronamide (Kerb). When EPA reassessed the registration of Pronamide in lettuce in 2009 they noted that data had been collected only for iceberg types and cancelled the registration for leaf lettuce. Dow Agrichemicals have been working to collect the needed data for leaf lettuce and expects the reregistration in November of this year.