Crabgrass Control From Tank Mixtures or Sequential Applications of Unlike Preemergence Herbicides.

Single spring applications of preemergence (PRE) herbicides are typical in areas with low crabgrass pressure, but for season-long control in areas with high crabgrass pressure sequential applications are used. It is typically recommended, based on early 1990’s research, to use the same active ingredient for both the initial and sequential applications. Objectives for this study were to determine if changing active ingredients (a.i.) for the initial and sequential application would affect crabgrass control and if single applications of tank mixed PRE herbicides would deliver season-long control. The study was conducted in Indiana in 2009, 2010, and 2011 and in Nebraska in 2011. Dithiopyr, pendimethalin, or prodiamine were applied in mid-April and mid-June as sequential applications using all possible combinations of the three herbicides and untreated for initial and sequential applications. The three herbicides were also applied mid-April as a single a.i. full rate or half rate application, or as a tank mixture with two a.i. at half plus half or half plus quarter rate. Sequential applications resulted in season-long crabgrass control regardless which of the three herbicides was used in the initial or sequential application. All tank-mixtures at a half plus half rate provided season-long control equivalent to full rate single a.i. applications. The ability to use different PRE herbicides for initial and sequential applications or in tank-mixture allows increased flexibility in crabgrass control programs.