Dustin F. Lewis, Travis W. Gannon, Fred H. Yelverton and Matt D. Jeffries

 Department of Crop Science, North Carolina State University, Raleigh, NC  27695

Location:  Block T29


Imprelis (active ingredient: aminocyclopyrachlor) is a newly developed synthetic auxin herbicide from DuPont that will soon be available for broadleaf weed control in warm- and cool-season turfgrass.  Imprelis has a broad spectrum of weed control with low use rates and a favorable environmental profile.  Preliminary reports indicate Imprelis is stable in aqueous environments but rapid photodecomposition can occur when exposed to sunlight.  In golf course management, most herbicide applications are made in the morning when dew is present.  If Imprelis applications were made to dew covered turf, there could be a potential for efficacy loss due to photodegradation.  Research was conducted to determine the effects of dew on Imprelis efficacy.


Research was conducted in 2009 at the North Carolina State University Lake Wheeler Turfgrass Unit in Raleigh, NC on ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. X C. transvaalensis Burtt-Davy]. ‘Tifway 419’ bermudagrass was selected because it displays an intermediate tolerance to Imprelis and retains dews well.  Experimental design was a randomized complete block with four replications in a factorial arrangement (five herbicide treatments by two moisture scenarios).  Herbicide treatments included:  two liquid applications of Imprelis at 4.5 fl oz/A (0.07 lbs ae/A) and 6 fl oz/A (0.09 lbs ae/A); two granular applications of Imprelis Elite and Standard granular at 150 lbs/A (0.075 lbs ae/A); aminopyralid at 8 fl oz/A  (0.125 lbs ae/A); and a nontreated check.  Moisture scenarios included DRY plots (no dew present) vs. WET plots (dew present).  DRY plots were covered overnight with tent structures to prevent dew formation.  WET plots were left uncovered so natural dew could form.  Structures were removed the following morning and herbicide applications were made with a CO2 pressurized spray boom calibrated to deliver 32.5 GPA.  Bermudagrass injury was visually rated on a 0-100% scale (0%=no visible turfgrass injury; 100%=complete turfgrass death).  In addition, turfgrass quality ratings were taken using a Field Scout TCM 500 NDVI Turf Color Meter on a 0-9 scale (0=poorest quality; 9=highest quality).


All herbicide treatments applied to WET plots showed greater injury than those applied to DRY plots 11 days after treatment (DAT).  Applied to WET plots liquid applications of Imprelis (4.5 and 6 fl oz/A), granular application of Imprelis Elite and Standard (150 lbs/A), and aminopyralid injured 30, 38, 15, 14, and 36%, respectively.  Applied to DRY plots, injury reduced to 25, 27, 10, 5, and 30%, respectively, for the same treatments.  Turfgrass quality ratings for liquid applications of Imprelis (4.5 and 6 fl oz/A) and aminopyralid on WET plots were 6.7, 6.5, and 6.4, respectively, compared to 6.8, 6.7, and 6.6, respectively, on DRY plots.


Both liquid applications of Imprelis provided greater injury and reduced turfgrass quality more when applied to WET vs. DRY plots 21 DAT.  Applied to WET plots, Imprelis (4.5 and 6 fl oz/A) injured 35 and 40%, respectively.  Applied to DRY plots, injury reduced to 28 and 30%, respectively.  Turfgrass quality ratings for Imprelis (4.5 and 6 fl oz/A) on WET plots were 5.9 and 5.5, respectively, compared to 6.4 and 5.9, respectively, on DRY plots.


These results indicated photodegradation did not occur when Imprelis was applied to dew-covered turfgrass.  Conversely, herbicidal efficacy increased when applications were made to WET plots vs DRY plots, which is similar to results observed in past research with other herbicide chemistries.