Author
|
Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only Publication Acceptance Date: 2/10/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Weed populations were affected by weed control history in 5-year field experiments. Two field experiments were conducted on adjacent fields and used the same design and treatment structure but differed in initial weed pressures. Each plot was subjected to the same weed control regime through the first 4 years of the experiments. Weed control treatments were a) weed-free, b) mechanical control, c) full-rate herbicide, d) banded herbicide, and e) variable postemergence. In the experiment where high density of giant foxtail initially dominated, plots kept weed free for 4 years averaged 24 giant foxtail (Setaria faberii Herrm.) plants m**-2 compared with 200 to 600 plants m**-2 following various herbicide and mechanical weed control treatments. The differences in weed density affected weed control with imazethapyr, and in the case of plots with a history of mechanical control, reduced soybean yield compared with the weed-free treatment. In the experiment with low initial weed density, wee control history had a lesser effect on weed densities and there was no effect on weed control with imazethapyr or soybean yield in treated plots. Differences in densities of annual broadleaf species also developed in response to treatment history. It appears that weed control practices that maintain weed populations below yield reducing levels do not result in weed populations that become high enough to reduce control efficacy in succeeding years. Weed-free conditions for 4 years greatly reduced weed densities, but enough weeds remained to reduce yields by 22% or more. Therefore, it seems questionable to attempt to maintain weed-free conditions in a soybean/corn system when the resulting weed populations still require treatment to prevent significant yield loss. |
