Published online by Cambridge University Press: 12 June 2017
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 officinale Weber), broadleaf dock (Rumex obtusifolius L.), buckhorn plantain (Plantago lanceolata L.), and red sorrel (Rumex acetosella L.). Three applications provided 100% control of seven of the eight remaining broadleaf perennials, including hedge bindweed (Convolvulus sepium L.) and Canada thistle [Cirsium arvense (L.) Scop.]; six of seven species of broadleaf annuals, including Pennsylvania smartweed (Polygonum pensylvanicum L.) and tumble pigweed (Amaranthus albus L.); 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 horizontalis Rend.). Three treatments of glyphosate at 2.2 kg/ha also increased the size of dwarf Japanese yews (Taxus cuspidata Sieb. & Zucc.) and two treatments at 4.5 kg/ha increased the size of boxleaf Japanese holly (Ilex crenata Thunb.).