Glyphosate [N-(phosphonomethyl)glycine] was applied at various stages of maturity to corn (Zea mays L. ‘Pioneer brand 3147’ and ‘Dekalb XL 394’), soybeans [Glycine max (L.) Merr. ‘Forrest’ and ‘Essex’], and johnsongrass [Sorghum halepense (L.) Pers.]. Glyphosate applied over-the-top of corn before the grain moisture level decreased to 30% (black layer will have been formed) caused various seed and subsequent progeny abnormalities. Depending on grain moisture level at the time of glyphosate application, seed weight was sometimes reduced and progeny seedling emergence, vigor, and weight were reduced. Also, abnormal seedlings, albino or straited, occurred. Glyphosate applied 2½ weeks or more before soybean maturity reduced seed weight, caused seed discoloration, and drastically reduced progeny seedling emergence, vigor, and weight. Glyphosate applied in September or early October controlled semimature johnsongrass. Later applications were less effective because of advanced senescence.

Hemp dogbane (Apocynum cannabinum L.) was investigated relative to seed germination, depth of seedling emergence, response to clipping, influence of soil type and fertility on vegetative growth, and herbicidal control. Seed germination in this study was influenced by light and scarification. Seedling emergence was influenced by the amount of soil cover. Soil type and fertility affected vegetative growth. In a greenhouse clipping study, hemp dogbane became perennial 41 days after emergence and by 65 days was producing more than one shoot per plant following clipping. Hemp dogbane was more completely controlled following September application of herbicide than from application made in June.

Seed dormancy of common milkweed (Asclepias syriaca L.) is broken by a few days of moist low-temperature after-ripening. The duration of low-temperature after-ripening of the seeds is temperature dependent. Seedling emergence is best when the seeds are planted 1 to 2 cm deep and extremely limited when planted 6 cm deep. Seedlings have the capacity to produce new shoots if clipped in the 1 to 1¾-leaf pair stage and multiple shoots if clipped in the 2 to 2½-leaf pair stage. All seedlings reaching the 4 to 4½-leaf pair stage before clipping produced new shoots.

Response of seedling alfalfa to four herbicides applied at the 2nd, 4th, and 8th trifoliate leaf stages was evaluated in 1988 and 1989. There was no interaction between the herbicides and alfalfa growth stages at the time of herbicide application in either year. Bentazon did not reduce alfalfa height or yield of the first cutting in either year. The dimethylamine salt of 2,4-DB and bromoxynil reduced first-cutting alfalfa yield in 1988 and 1989, respectively, and the butoxyethanol ester of 2,4-DB reduced first-cutting alfalfa yield both years. Each herbicide affected one or more measurements of alfalfa quality in at least one year.