Aminocyclopyrachlor Safety In Seeded Cool-Season Turfgrass.

Turfgrass managers applying aminocyclopyrachlor for annual and perennial broadleaf weed control in cool-season turfgrasses may want to seed into treated areas. Field experiments were conducted in Georgia (GA), Tennessee (TN), and Texas (TX) from August 2010 to March 2011 to investigate perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) reseeding intervals following aminocyclopyrachlor applications. The experimental design at each site was a randomized complete block with four replications. Four herbicide treatments were applied at four application timings before seeding, in addition to a non-treated control. Aminocyclopyrachlor was applied at 2.25, 4.5, and 9 kg ai ha^-1 while 2,4-D + dicamba + MCPP was applied at 1.5 kg ai ha^-1. Herbicide treatments were applied 0, 2, 4, or 6 weeks before seeding (WBS). Aminocyclopyrachlor rates were selected from previous research evaluating broadcast applications of aminocyclopyrachlor for selective broadleaf weed control. The 2,4-D + dicamba + MCPP rates were selected from label recommendations. Treatments were applied to 1 x 3.6-m plots in GA, TN, and TX. On the day of seeding, the field was mowed to 3.8 cm with a rotary mower, debris was removed, and the seedbed received two additional passes with a vertical mower set to a depth of approximately 1.3 cm. ‘Titan’ tall fescue and ‘Manhattan IV’ perennial ryegrass were seeded separately and perpendicular to herbicide treatments over half of all the plots at 390 kg ha^-1 with a drop spreader. Herbicide treatments scheduled for the day of seeding were applied immediately after seeding each grass species. After seeding, tall fescue and perennial ryegrass were irrigated daily to promote germination and establishment. A 10-10-10 (N-P₂O₅-K₂0) granular fertilizer was applied at 48 kg N ha^-1 approximately 4 weeks after seeding (WAS) at each location. Tall fescue and perennial ryegrass cover was assessed visually, for each species 2, 4, 8, 12, and 20 WAS on a percent scale (0 equaled no turf cover and 100 equaled complete turf cover). Data were subjected to analysis of variance with main effects and all possible interactions tested using the appropriate expected mean square values. No location x treatment interactions were detected for tall fescue or perennial ryegrass cover so data were pooled across locations. Means were separated using Fisher’s protected LSD test at the 0.05 probability level. Perennial ryegrass and tall fescue establishment was similar for the untreated treatments, aminocyclopyrachlor treatments, and 2,4-D + dicamba + MCPP applied at 0, 2, 4, or 6 WBS. Results suggest tall fescue and perennial ryegrass can be safely seeded the day of aminocyclopyrachlor applications at 2.25, 4.5, and 9 kg ai ha^-1.