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BIOLOGY AND CONTROL OF COMMON MILKWEED
Abstract
Visual surveys conducted across eastern and southeastern Nebraska revealed all cropland and noncropland situations to be infested, to some degree, with common milkweed (Asclepias syriaca L.). In descending order, soybeans {Glycine max (L.) Merr.}, oats (Avena sativa L.), railroad rights-of-way, sorghum {Sorghum bicolar (L.) Moench}, fallow land, and roadsides were infested to the greatest extent. In cropland situations, alfalfa (Medicago sativa L.), pasture, winter wheat (Triticum aestivum L.), and corn (Zea mays L.) were generally the least infested areas. Average common milkweed populations across corn, sorghum, and soybean fields ranged from 11,100 to 45,200 plants/ha. Crop grain yield losses associated with common milkweed infested areas averaged 2 to 10% for corn, 4 to 29% for sorghum, and 12 to 19% for soybeans. Progressively greater grain reductions were generally associated with increasing common milkweed population. Growing medium conductivity below 7 and 13 mmhos/cm('2) did not effect germination percentage, hypocotyl length, or radicle length of common milkweed or sorghum seedlings, respectively. Altering pH of the growing medium from 4 to 10 had no significant effect on common milkweed or sorghum germination percentage, hypocotyl length, or radicle length. Reductions in all three parameters for both species occurred at pH 2. Experiments using undiluted aqueous extracts of common milkweed shoot and root material showed a possible allelopathic influence of common milkweed on sorghum germination percentage, hypocotyl length, and radicle length. No allelopathic influence could be shown using common milkweed residues decomposed in soil for up to 5 months or a stairstep apparatus to eliminate direct contact and competition of common milkweed and sorghum. In greenhouse experiments postemergent treatments of amitrole (3-amino-s-triazole) in combination with 2,4-D {(2,4-dichlorophenoxy)acetic acid}, dicamba (3,6-dichloro-o-anisic acid); and glyphosate {N-(phosphonomethyl)glycine} alone or in combination with 2,4-D or dicamba effectively reduced dry-weight of 6-weed-old common milkweed regrowth. Removal of treated top-growth as soon as 1 day after treatment did not effect growth reduction from glyphosate. Using ('14)C-2,4-D and ('14)C-glyphosate to measure absorption into greenhouse grown common milkweed there was no significant increase in absorption 12 days after treatment as compared with 3 days after treatment. Greater amounts of 2,4-D were absorbed and translocated from the treated leaf area than glyphosate. However, movement of ('14)C out of the treated leaf area showed more ('14)C-2,4-D remaining in the untreated portion of the treated leaf than glyphosate. In field experiments, excellent control of common milkweed could be obtained with a broadcast application of glyphosate at 2.2 kg/ha or glyphosate + amitrole at 1.1 + 4.5 kg/ha at the early bud growth stage. Control varied among locations and years. Herbicides applied with the herbicide glove or roller applicator gave control of common milkweed similar to that obtained from broadcast applications.
Subject Area
Agronomy
Recommended Citation
CRAMER, GARY LYNN, "BIOLOGY AND CONTROL OF COMMON MILKWEED" (1980). ETD collection for University of Nebraska-Lincoln. AAI8109980.
https://digitalcommons.unl.edu/dissertations/AAI8109980