Bioherbicide Treated Mulches for Ornamental Weed Control

The provinces of Quebec and Ontario have implemented bans on all “cosmetic pesticide" applications, prompting research in alternative weed controls for nurseries and especially in the landscape industry.  Evaluations initiated on May 19, 2009 at Sheridan Nursery, Halton Hills, Ontario in one gallon containers, 75°F in full sun and June 8, 2010 at the Vineland Research and Innovation Centre, Victoria Rd. Farm, Vineland Station, ON, in 2” mulched 3X3 ft. plots at 80°F in full sun were conducted.   In 2009, two sizes of Pine bark of >1” and <1” were obtained from Gro-Bark Ltd., Caledon, ON.  In 2010, three bark types were used: Pine <1” as in 2009; Hardwood (bark and wood); and, Cedar (bark and wood) obtained from Gro-Bark Ltd.  In both years bark was spread on plastic sheets at two inches thick with five replications per treatment and sprayed.  The treated bark was allowed to stand for 24 hr. and applied to the tops of freshly planted one-gallon containers in 2009 or plots in 2010.  In 2009, oxadiazon (Ronstar, Dow AgroSciences) and flumioxazin (BroadStar, Valent USA) at 1X rates were used as industry standards for efficacy and phytotoxicity comparisons.  Extracts of two alleopathic plants called BH1 and BH2 were also prepared and applied at 5% and 10% aqueous solution.  In 2010, phytotoxicity evaluations were conducted on white spruce (Picea gluaca) English oak (Quercus robur) and Coreopsis ‘Moonbeam.’  In 2009, Euonymus fortunei 'Emerald Gaiety' (Winter Creeper Euonymus), Sambuscus canadensis (American Elderberry) and Pinus Mugo (Mugo Pine) were used.  In 2009, 200 grain vinegar (Ohio State University (OSU), Food Science Department) applied on < 1” pine bark was as efficacious as the standard Ronstar with less than half the phytotoxicity at 90 DAT. The BH1 plant extract at 5 and 10% on <1” bark was as efficacious as Vinegar <1” and the Ronstar; however, the phytotoxicity with BH1 was almost half that of 200 grain vinegar and 3.5 X less than Ronstar.  In 2010, further testing with horticultural vinegars compared to the OSU 200 grain, pelargonic acid (Scythe™ at 10% v/v), (Gowan Co., LLC, Yuma, AZ) and comparisons of various mulch types were conducted. In 2010, Munger Horticultural Vinegar Plus (MHVP) (20% acetic acid) (Engage Agro, Guelph, ON) outperformed the 200 grain vinegar and WeedPharm™ (20% acetic acid) at 10% v/v (Pharm Solutions Inc., Port Townsend, WA).  MHVP, Scythe and BH1 were the most efficacious treatments in 2010.