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United States Department of Agriculture

Agricultural Research Service

Title: Timing and Measurement of Weed Seed Shed in Corn

Authors
item Forcella, Frank
item Peterson, Dean
item Barbour, James - UNIVERSITY OF MINNESOTA

Submitted to: Weed Technology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 26, 1996
Publication Date: N/A

Interpretive Summary: Timing of weed seed shed in corn was studied in a cool-wet year (1993) and a warm-dry year (1994) in west central Minnesota. Sound (apparently viable) seed varied from 11% (1993) to 59% (1994) and averaged 35% of total seed production for redroot pigweed. Sound seed percentages were more consistent for other species, averaging 79% for green foxtail, 68% for wild mustard, 49% for Pennsylvania smartweed, and 48% for common lambsquarters. Seed shed commenced in late August in 1993 and early August in 1994. Average growing degree days (base 10 C) accumulated from planting until 25% seed shed was 951 for wild proso millet, 983 for common lambsquarters, 984 for wild mustard, 1004 for Pennsylvania smartweed, and 1034 for both green foxtail and redroot pigweed. Wind storms dispersed large percentages of total seeds within a single day. Greater than 1/5 of all sound seed of green foxtail, redroot pigweed, and common lambsquarters were retained by the seedheads and dispersed by combines at harvest. In contrast, seeds of early-maturing species, such as wild mustard and proso millet, were completely dispersed by harvest time in 1993, but 1/3 of seeds were retained by seedheads until harvest in 1994. The best design for a seed trap consisted of a 4 inch diameter plastic cup, whose bottom was replaced by a brass screen, and the entire unit attached to a small wooden stake for support. These results can be used to schedule better timing of rope-wick or roller herbicide applications for reducing production of weed seeds, and they can be used to determine the potential contribution of combine harvesting to weed seed dispersal.

Technical Abstract: Extent and duration of weed seed shed was measured for two years in maize crops that received cultivation but no herbicides. Percentage of seed production represented by sound (filled) seed was 79% for green foxtail, 68% for wild mustard, 49% for Pennsylvania smartweed, 48% for common lambsquarters, and 35% for redroot pigweed. Percentage sound seed varied from 11% (1993) to 59% (1994) for redroot pigweed, but was more stable for other species. Seed shed commenced in late August in a cool year (1993) and early August in a warm year (1994). Average GDD (base 10 C) accumulated from planting until 25% seed shed was 951 for wild proso millet, 983 for common lambsquarters, 984 for wild mustard, 1004 for Pennsylvania smartweed, and 1034 for both green foxtail and redroot pigweed. Brief wind storms may have dispersed large percentages of total seed production. Greater than 1/5 of all sound seed of green foxtail, redroot pigweed, and common lambsquarters were retained by the seedheads and dispersed by combines at harvest. In contrast, seeds of early- maturing species, such as wild mustard and proso millet, were completely dispersed by harvest time in the warmer year, but 1/3 of seeds were retained by seedheads until harvest in the cooler year. Measurement of seed shed was compared using five seed trap designs. The preferred design consisted of a 10 cm diameter plastic cup, whose bottom was replaced by a brass screen, and the entire unit attached to a small wooden stake for support. This design provided high estimates of seed production, least among-replication variability, highest correlation with weed population density and aboveground dry-weight, lowest assembly cost, and greatest ease for sample access and seed processing.

Last Modified: 10/20/2014
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