Herbicide-Treated Mulches for Weed Control in Nursery Container Crops

Abstract

Abstract Weed control is the largest expense faced in the nursery and landscape industries. Nursery growers spend $967 to $2,228/A, depending on species, for supplemental hand weeding in addition to three to four yearly herbicide applications. Herbicide-treated mulches have utility in addressing many current nursery/landscape weed control issues such as non-target herbicide losses, leaching and off-site herbicide movement, and reduction of weed control costs. The objectives of this study were to compare seven types of mulches, including Douglas fir nuggets, pine nuggets, shredded hardwood, shredded Cypress, PennMulch™, rice hulls, and cocoa shells sprayed with Surflan [aqueous solution (AS) (oryzalin) at 1.12 (0.5×) and 2.24 (1×) kg ai/ha (1.0 and 2.0 lb ai/A)] and SureGuard [(water dispersible granular (WDG) (flumioxazin) at 0.19 (0.5×) and 0.38 (1×) kg ai/ha (0.17 and 0.34 lb ai/A)] to determine efficacy on common chickweed (Stellaria media), annual bluegrass (Poa annua) and spotted spurge (Chamaesyce humistrata) and phytotoxicity to Golden vicary privet (Ligustrum × vicaryi), creeping juniper (Juniperus horizontalis ‘P.C. Youngstown’), and wintergreen boxwood (Buxusmicrophylla ‘Wintergreen’) at 45 and 115 days after treatment (DAT). The herbicide-treated mulches were compared to untreated mulches, over-the-top sprays of the herbicides and a combination spray of Surflan + SureGuard each applied at the 1× rate, described above, an industry-standard granular formulation Rout (oxyfluorfen + oryzalin) at 3.41 kg ai/ha (3.0 lb ai/A), an industry standard nonchemical alternative Geodisc™, and an untreated control. The experiment was conducted in 2001 and repeated in 2002. In 2001, 17 of 43 treatments provided commercially acceptable visual ratings at 45 DAT; 14 were herbicide treated mulches. Four of five treatments in 2001 providing acceptable control at 115 DAT were herbicide treated mulches. In 2002, three treatments providing commercially acceptable control at 45 DAT were: PennMulch™ + 0.5 × Surflan, PennMulch™ + SureGuard, and Rout. Rout was the only treatment providing commercially acceptable control at 115 DAT in 2002. Golden vicary privet exhibited the greatest phytotoxicity in both years. In 2001-2002, the over-the-top sprays of Surflan + SureGuard were the most phytotoxic treatments to Golden vicary privet when averaged across 45 and 115 DAT. The data indicated a significant herbicide × mulch interaction and that some combinations, such as hardwood + SureGuard or pine nuggets + SureGuard, increased and extended efficacy and reduced phytotoxicity versus mulches or herbicides applied alone.