- Weed interference is a major, ongoing pest problem in sweet corn and a diverse community of weeds persists until harvest in most fields. Impact herbicide was used for the first time in 2006 with great success, and a registration for Laudis was granted in November of 2007. These registrations have significantly reduced wild proso millet populations in the Willamette Valley. Issues persist with the use of these herbicides, however. First is the fact that atrazine greatly improves efficacy on some species and, therefore, is typically tankmixed with HPPD herbicides, particularly if triazine resistant species are present. Although atrazine has been an important herbicide to corn production for over 50 years in North America, it is under fire. Registered use rates have been in decline for several decades, and atrazine use is increasingly being prohibited in specific watersheds. The herbicide has been withdrawn from use throughout many European countries due to persistence of atrazine and its breakdown products in the environment and concentration of these in ground and surface water. Similar issues are on the horizon in Oregon.