Mesotrione Activity on Large Crabgrass Is Influenced By Nitrogen Fertilization Rate and Application Timing.

Mesotrione, a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicide is labeled for the postemergence control of numerous grassy weeds. It has enhanced efficacy on large crabgrass (Digitaria sanguinalis) when applied in conjunction with soil-applied nitrogen (N). Greenhouse studies were conducted in Indiana (IN) and Tennessee (TN) to determine the influence of N rate and tissue N concentration, and the influence of N application timing on mesotrione activity in large crabgrass. Large crabgrass plants that received 12 kg N ha^-1 or higher prior to mesotrione application had higher levels of bleached and necrotic leaves compared to plants that received 0 kg N ha^-1 7 days after treatment (DAT). While we tested N application rates as high as 98 kg N ha^-1, 90% of the maximum bleached and necrotic leaves could be achieved with applications of 10.1 or 8.9 kg N ha^-1 in our two experimental runs. Nitrogen concentration in large crabgrass leaf and stem tissue on the day of the mesotrione application was closely related to the bleached and necrotic symptoms observed 7 DAT. Nitrogen application timing was also important with N application 3, 1, and 0 days before a mesotrione application having the highest percentages of bleached and necrotic leaves. As a result, practitioners can pair their N and postemergence mesotrione applications together or in close proximity to enhance large crabgrass control.