No abstract

Infestations of common milkweed (Asclepias syriacaL.), in descending order of incidence in Nebraska, occurred on areas occupied by soybean [Glycine max(L.) Merr.], oats (Avena sativaL.), sorghum [Sorghum bicolor(L.) Moench.], railroad rights-of-way, fallow land, roadsides, corn (Zea maysL.), winter wheat (Triticum aestivumL.), pasture, and alfalfa (Medicago sativaL.). Average crop yield reductions, within common milkweed communities of 11100 to 45 200 plants/ha, ranged from 2 to 10% for corn, 4 to 29% for sorghum, and 12 to 19% for soybeans. Reductions in crop yields tended to increase with increasing common milkweed populations. Germination percentage of common milkweed and sorghum were not significantly affected by growing medium conductivities below 7 and 13 mmho/cm2, respectively. Growth media at pH 2 significantly reduced germination percentage, hypocotyl length, and radicle length of both common milkweed and sorghum as compared with pH 4 to 10. Undiluted aqueous extracts of common milkweed shoot and root material significantly reduced germination percentage, hypocotyl length, and radicle length of sorghum.

Griin' (Reg. No. CV-25, PI 672148), is a canola-quality, winter oilseed rape (Brassica napus L.) and is a dual-purpose forage and grain canola cultivar developed for Kansas, with potential to be grown across the southern Great Plains. It was tested as the experimental cultivar KS4022 and was released by K-State Research and Extension. The ability of Griin to withstand the efects of simulated grazing and its excellent forage quality compared with 'Wichita' make it a good candidate for dualpurpose use. In simulated grazing studies, Griin had winter survival superior to Wichita across all treatments; Griin averaged 80.4% survival across grazing treatments, whereas Wichita averaged 69.4%. At the optimum timing for forage harvest, Griin's inal grain yield was reduced by 36.6%, while Wichita's inal grain yield was reduced by 61.1% compared with the no-forage harvest treatment. Griin yields a highprotein, highly digestible, nutritious forage for livestock producers. Griin also possesses beneicial morphological features that could be used in breeding of new cultivars. A prostrate growth habit and the ability to avoid fall stem elongation are important characteristics to consider when selecting a canola cultivar with optimum winter survival.

Control of common milkweed (Asclepias syriacaL.) with postemergence herbicides was investigated in greenhouse and field experiments. In greenhouse experiments, amitrole (3-amino-s-triazole), dicamba (3,6-dichloro-o-anisic acid), glyphosate [N-(phosphonomethyl)glycine], and combinations of amitrole + dicamba, dicamba + 2,4-D [(2,4-dichlorophenoxy) acetic acid], glyphosate + 2,4-D, and glyphosate + dicamba reduced regrowth of 6-week-old common milkweed as compared with the untreated check. Postemergence herbicides commonly used in corn (Zea maysL.), sorghum [Sorghum bicolor(L.) Moench], and soybeans [Glycine max(L.) Merr.] had little effect on emerged common milkweed. Removal of common milkweed top-growth as early as 1 day after treatment did not effect subsequent growth reduction from glyphosate at 0.3 kg/ha or higher. In the field, satisfactory control (70% or better) of common milkweed was obtained with glyphosate at 2.2 kg/ha applied at the early or late bud growth stage. Plots plowed 1 day after application of glyphosate at 2.2 kg/ha still retained satisfactory control of common milkweed 1 yr after treatment. Herbicides applied with a herbicide glove or a roller applicator resulted in common milkweed control similar to that obtained from broadcast spray applications.