Concerns about atrazine carryover this year

Jim Martin and J.D. Green, Extension Weed Scientists, University of Kentucky

Dry soil conditions can enhance persistence of herbicides such as atrazine. Kentucky has had dry seasons in the past, yet atrazine injury to rotational crops was seldom an issue. Having said that, the risk of crop injury due to atrazine carryover is still an issue that we need to consider on a case by case basis. The risk will be reduced if atrazine was applied early spring and had some rain to move into the soil profile. Prolonged periods of dry soil will enhance persistence and increase the chance of injuring rotational crops. If weather conditions improve and we have a mild and wet fall and winter, then the risk of carryover to spring planted crops will be reduced. Using high rates of atrazine will increase the risks. Atrazine may dissipate more rapidly in no-till compared with tilled conditions. High soil pH (pH >7.0) will increase atrazine persistence.

Simazat Fall Applications and Atrazine Stewardship

Jim Martin, J.D. Green, and Bill Witt, Weed Specialists, University of Kentucky

On July 14, 2011 the EPA approved a supplemental label for using of Simazat (a premix of atrazine and simazine) for fall applications to control winter-annual broadleaf weeds prior to next year’s corn crop. The recently approved label is the only one that allows the use of atrazine in the fall in Kentucky. A lot of resources have been invested over a period of several years defending the registration of atrazine. In order to maintain atrazine as a viable option for weed management in Kentucky, it is important that applicators are not complacent in regards to its potential impact on the environment. Label restrictions concerning Simazat’s use near ground and surface waters are particularly important when it is applied in the fall.  Highly erodible fields with little to no vegetation, or residue cover, are especially at risk of movement of atrazine or simazine from the treated area. Certain watersheds, including portions of the Green River and Rough River are being monitored for atrazine and simazine. It is also important to consider the rate of atrazine and simazine. The recommended rate for fall applications is 2.5 pt of Simazat 4L/A. This is equivalent to 0.625 lb ai atrazine/A plus 0.625 lb ai simazine/A for a total amount of 1.25 lb ai/A. If Simazat is applied in the fall, do not exceed 2.5 pt Simazat 4L/A preemergence the following spring. When tank mixing or sequentially applying products containing atrazine and/or simazine, the cumulative amount of active ingredient of atrazine and/or simazine per calendar year must not exceed 2.5 lb ai/A.  If using the Simazat 90DF formulation, consult label for the maximum use rates.