Public pressure to ban or limit synthetic pesticide use on turfgrass has greatly increased the past few years.  Very little research has been published or presented concerning alternatives to synthetic herbicides for broadleaf weed control in turfgrass.  A 3-year study was conducted to evaluate broadleaf weed control in turfgrass using various alternatives to synthetic herbicides.

In September 2009, 11 treatments were applied to a lawn area in Doylestown, PA that contained about 20% broadleaf weeds and 80% cool-season turfgrasses.  Treatments included hand-pull, Burnout II (citric acid, clove oil, sodium lauryl sulfate), Weed-A-Tak (clove oil, phenethyl propionate, corn gluten meal), household vinegar, compost, corn gluten meal, glyphosate, synthetic herbicide (2,4-D, MCPP & dicamba), Burnout II/seed perennial ryegrass, an experimental organic extract, and an untreated control.  Treatments that were liquids were applied as spot treatments for the weeds using a hand-pump spray bottle and were re-applied 7 days after initial application to any remaining weeds.  On adjacent sites, the study was repeated in September 2010 and September 2011 with 4 additional treatments— FeHEDTA, propane torching, ammoniated soap of fatty acids, and sodium tetraborate.  Weeds were spot-treated 0 and 14 days after initial treatment (DAIT) for all treatments except corn gluten meal and compost which were blanket treatments. 

Percent weed cover by weed species was evaluated approximately every 7 DAIT for 70 days.  Since each weed species did not always appear in each plot, percent weed cover by species were combined for each plot.  Statistical analysis was conducted on total percent weed cover data since treatments had similar percent weed cover at 0 DAIT.  Total percent weed cover data were subjected to the square root transformation to stabilize variance and then subjected to ANOVA with means separated with Tukey’s HSD.  Untreated control plots were included in statistical analysis.  Turf quality was assessed visually according to NTEP standard practices where 9 was outstanding or ideal turf and 1 was the poorest or dead turf.  A rating of 6 or greater was considered acceptable.

Most treatments significantly reduced percent weed cover, however some of these treatments (Burnout II, Weed-A-Tak, glyphosate, vinegar, organic extract, ammoniated soap of fatty acids) killed turfgrass as well and resulted in very poor turf quality.  Hand-pull, FeHEDTA, and the synthetic herbicide treatments killed the weeds without decreasing turf quality.  Some treatments (hand-pull, Burnout II, Weed-A-Tak, glyphosate, FeHEDTA, ammoniated soap of fatty acids, organic extract) controlled weeds as well as the synthetic herbicide.  Various treatments needed multiple applications since the initial application caused only leaf necrosis and the weed resurged.  The corn gluten meal and compost treatments did not significantly control weeds compared to the untreated control. The corn gluten meal significantly improved turf quality, however, growth was excessive.