Studies examined the effect of herbicides on the quality and root strength of winter-installed tall fescue and hybrid bermudagrass sod. Sod was installed in February and treated approximately 30 to 45 d after installation with a variety of preemergence (PRE) and postemergence (POST) herbicides. Tall fescue quality was not affected by any herbicide treatment in 2000 or 2001. Root strength reduction occurred only in 2001 by dithiopyr applied PRE at 2.5 kg ai/ha, which is 4.5 times the maximum use rate. No other herbicides decreased tall fescue root strength in either year. Bermudagrass quality was decreased by triclopyr plus clopyralid applied POST, which resulted in 22 and 6% injury 42 d after initial treatment (DAIT) in 2000 and 2001, respectively. However, POST herbicides did not affect bermudagrass root strength in either year. PRE herbicide treatments did not reduce root development in bermudagrass in 2000. However, dithiopyr applied at 0.84 and 2.5 kg/ha reduced bermudagrass rooting by 59 and 70%, 60 DAIT, in 2001. Pendimethalin reduced root development of bermudagrass by 62% when applied at 10.2 kg/ha, three times the maximum use rate, in 2001. However, by 120 DAIT, only dithiopyr applied at 2.5 kg/ha decreased bermudagrass root development.
Nomenclature: Clopyralid; 2,4-D; dicamba; dithiopyr; MCPP; oxadiazon; pendimethalin; pronamide; simazine; triclopyr; hybrid bermudagrass, Cynodon transvaalensis Burtt-Davy × Cynodon dactylon (L.) Pers. ‘Tifway II’; tall fescue, Festuca arundinacea Schreb. #3 FESAR ‘Rebel II’.
Additional index words: Dynamometer, root strength.
Abbreviations: DAIT, days after initial treatment; fb, followed by; POST, postemergence; PRE, preemergence; 3×, three times the maximum labeled use rate; 4.5×, four and a half times the maximum labeled use rate.