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Weeds: Coexistence or Control¹

ABSTRACT

This presentation is a review of literature with the purpose of exposing the direct role weeds have in affecting the well being of man and animal. Mankind working to feed its masses cannot afford weeds which captivate crop fields, nor can it afford not to use chemical energy to control these weeds.

Weeds are vigorous competitors with crops causing severe yield losses as well as many indirect losses such as increased production and transportation costs. For example, the yield reduction from infestations of less than one plant/30 cm of row was 40,300 kg/ha or 51% from kochia (Kochia scoparia L. Schrad.) in sugarbeets (Beta vulgaris L.), 600 kg/ha or 27% from smooth pigweed (Amaranthus hybridus L.) and 21% from wild mustard (Brassica kaber D. C.) in soybeans (Glycine max L. Merr.), and from 100 wild mustard plants/0.9 m², 36% in wheat (Triticum aestivum L.), 29% in barley (Hordeum vulgare L.), 32% in oats (Avena sativa L.), and 88% in flax (Linum usitatissimum L.). The degree of competition from a weed is dependent upon the crop, climatic, and edaphic factors. Protein of wheat, cotton lint grade, flax oil and iodine value, and potato grade have been reduced by weed competition. Weed seed contamination of grain may impart objectional flavors to the marketed product, render grain unfit for seed, and cause storage problems.

Common ragweed (Ambrosia artemisiifolia L.) and giant ragweed (A. trifida L.), which both adversely affect 4% of the population, account for 40% of the late summer pollen polluting the air. Many weeds are toxic to man and animals causing discomfort, congenital defects, and death. Three to five percent of the cattle, sheep, and horses on Western ranges in the United States are killed by consuming poisonous weeds each year.

Key Words: weed competition • weed toxicity • social aspects of weeds

¹ Published with the approval of the Director of the North Dakota Agr. Exp. Sta. Paper presented Aug. 18, 1971, in New York City at the annual meeting of the ASA as part of the Division C-3 symposium "Fate and Economic Impact of Herbicides."

² Professor, Agronomy Dep., North Dakota State Univ., Fargo, 58102.

Received for publication December 28, 1971.