Glyphosate and Paraquat Effectiveness in Woody Nursery Stock

Abstract

Six species of 2- or 3-yr-old woody nursery stock were planted in the field in May 1976. Glyphosate [N-(phosphonomethyl) glycine] at 2.2 or 4.5 kg/ha or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 0.6 or 1.1 kg/ha were applied one or two times as directed sprays in 1976 and one, two, or three times each season in 1977 and 1978. Three applications of glyphosate or paraquat were required to control weeds during the entire growing season. When late-season applications of glyphosate were made during 1977, residual weed control was observed during early 1978. When glyphosate was applied twice a year for 3 yr at 4.5 kg/ha, four of the previously dominant perennial weeds were controlled, including common dandelion (Taraxacum officinaleWeber), broadleaf dock (Rumex obtusifoliusL.), buckhorn plantain (Plantago lanceolataL.), and red sorrel (Rumex acetosellaL.). Three applications provided 100% control of seven of the eight remaining broadleaf perennials, including hedge bindweed (Convolvulus sepiumL.) and Canada thistle [Cirsium arvense(L.) Scop.]; six of seven species of broadleaf annuals, including Pennsylvania smartweed (Polygonum pensylvanicumL.) and tumble pigweed (Amaranthus albusL.); and all of the remaining grass weeds. Crop size, crop quality, and marketability of the six ornamental species were not adversely affected by either herbicide. Two or three applications of glyphosate at 2.2 kg/ha or two treatments at 4.5 kg/ha increased plant size of andorra junipers (Juniperus horizontalisRend.). Three treatments of glyphosate at 2.2 kg/ha also increased the size of dwarf Japanese yews (Taxus cuspidataSieb. & Zucc.) and two treatments at 4.5 kg/ha increased the size of boxleaf Japanese holly (Ilex crenataThunb.).