2008 Joint Annual Meeting (5-9 Oct. 2008): Postemergent Application of Dithiopyr for Control of Crabgrass (Digitaria species) in Turfgrass.

Crabgrass (Digitaria species) is one of the most common weeds that infest managed turfgrass around the world. The two primary species, smooth crabgrass (D. ischaemum Schreb. ex Muhl.) and large or hairy crabgrass (D. sanguinalis (L.) Scop.), are annual grasses which were introduced from Eurasia and now are widespread throughout the United States.  They emerge in early to mid spring and are killed by the first fall frost.  Crabgrass flowers throughout the summer and is a prolific seed producer that can rapidly dominate desirable turfgrass.  It is a vigorous plant that can grow faster than most desirable turfgrass species when exposed to adverse conditions such as drought, heat and low fertility where turfgrass suffers.  Dithiopyr (3,5- pyridinedicarbothioic acid, 2-(difluoromethyl)- 4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-dimethyl ester) has been used widely for a number of years by turfgrass managers for preemergent crabgrass control.  Previous research has demonstrated that postemergent crabgrass control can be obtained when dithiopyr is applied prior to the tillering of crabgrass (less than 5 leaves per plant).  The field performance data demonstrate that postemergent application of dithiopyr prior to tillering is effective in controlling crabgrass.