Dimension® 2EW is a new formulation of dithiopyr widely used for pre-emergence control of crabgrass in the Transition Zone and Northern United States.  Dithiopyr also controls crabgrass post-emergence and up to the tillering stage.  Defendor™ (florasulam) is a new herbicide from Dow® AgroSciences, utilizing low use rates for post-emergence control of many winter annuals and perennial broadleaf weeds.  Defendor™ should be available to the public in early 2013 as a co-pack with Dimension® 2EW offering pre-emergence crabgrass control and broadleaf weed suppression during the lag time between pre-emergence crabgrass treatment and late season broadleaf treatments.      

A study was initiated on March 16, 2012 that evaluated the following treatments for broadleaf weed control: dithiopyr (280 g ai ha^-1) + florasulam (14.6 g ai ha^-1) applied in mid-March + 6 weeks after initial treatment (WAIT), dithiopyr (280 g ai ha^-1) + florasulam (14.6 g ai ha^-1) + Trimec Classic (1330 g ai ha^-1) at 6 WAIT, dithiopyr (426 g ai ha^-1) + florasulam (14.6 g ai ha^-1) applied in mid-March, dithiopyr (426 g ai ha^-1) + florasulam (14.6 g ai ha^-1) applied in early May, dithiopyr (426 g ai ha^-1) + Trimec Classic (1330 g ai ha^-1) applied in early May and dithiopyr (280 g ai ha^-1) applied mid-March + 6 WAIT.  A second study, also initiated March 16, 2012, evaluated dithiopyr alone for smooth crabgrass control applied at 426 g ai ha^-1 in mid-March, 280 g ai ha^-1 applied in mid-March and mid-May, and 560 g ai ha^-1 applied in mid-March.  Both studies were arranged as a randomized complete block design with three replications.  All treatments were applied at 280 L ha^-1 using Teejet turbo twin injection 11004 nozzles at 262 kPa.  An untreated check was included for comparison. 

In the first study, all treatments controlled white clover greater than 93% when evaluated on June 15 (4 months after initial treatment), with the exception of dithiopyr (426 g ai ha^-1) + florasulam (14.6 g ai ha^-1) applied at 6 WAIT, and dithiopyr (280 g ai ha^-1) applied twice, which controlled white clover 30% and 10%, respectively.  On the same evaluation date, dithiopyr + florasulam treatments and treatments that contained Trimec Classic controlled dandelion > 93%, and the remaining treatments controlled dandelion < 25%.  These results indicate that dithiopyr plus florasulam controls white clover, but only when applied early in the season.  Dithiopyr applied alone does not control white clover.  Acceptable control of dandelion was achieved when dithiopyr was paired with florasulam at 6 WAIT and when treatments contained Trimec Classic.  In the second study, smooth crabgrass was completely controlled by all treatments on August 17, 2012, indicating dithiopyr applied alone and as a sequential application will provide season-long control of smooth crabgrass in the Transition Zone.  At a second location, single treatments of dithiopyr controlled smooth crabgrass less than the split treatment of 280 g ai ha^-1 applied in March and May.