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Advances in Witchweed Control

Published online by Cambridge University Press:  12 June 2017

W. C. Shaw ,
D. R. Shepherd ,
E. L. Robinson  and
P. F. Sand
W. C. Shaw
Affiliation:
Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Maryland and Whiteville, North Carolina
D. R. Shepherd
Affiliation:
Plant Pest Control Division, Agricultural Research Service, U. S. Department of Agriculture, Washington, D. C. and Whiteville, North Carolina
E. L. Robinson
Affiliation:
Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Maryland and Whiteville, North Carolina
P. F. Sand
Affiliation:
Plant Pest Control Division, Agricultural Research Service, U. S. Department of Agriculture, Washington, D. C. and Whiteville, North Carolina
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Abstract

Witchweed (Striga asiatica), a parasitic chlorophyll-bearing plant (Scrophuladiaceae) which attacks corn, sorghum, sugarcane, and more than 60 other important crop plants and weeds belonging to the grass family, was found in North Carolina and South Carolina in 1956. It presents a potential hazard to the production of grain crops with an annual value of more than 5 billion dollars in the United States. Continued extensive surveys indicate that witchweed is now present in 20 counties in North Carolina and 10 in South Carolina on a total of 9,566 farms containing 210,671 acres. Federal interstate and state intrastate quarantines (the first for a weed in the U. S.) were established to reduce its spread. Witchweed produces up to 500,000 microscopic longlived seeds per plant. These do not usually germinate until stimulated by a chemical stimulant secreted by the roots of certain plants. A stimulant has been isolated from corn but its exact chemical structure has not be determined. More than 300 chemicals have been evaluated in the laboratory in attempts to find a synthetic stimulant. Of these, 18 stimulated witchweed seed germination in the laboratory but they have not been evaluated for their effectiveness in controlling witchweed under field conditions. After 4 years of catch or trap crops, excellent control of witchweed has been obtained and highly profitable crops of corn have been produced on heavily infested land. Corn grown continuously with witchweed seed production prevented by 2,4-dichlorophenoxyacetic acid [2,4-D] has resulted in excellent witchweed control and high corn yields. Corn grown continuously receiving 2,3,6-trichlorophenylacetic acid [fenac] as a pre-planting soil-incorporated treatment and 2,4-D as a post-emergence spray as needed have proved effective full-season control of witchweed. Tobacco and certain other crops cannot be grown in rotation with corn for a period of 2 years after this treatment because of fenac residues in the soil. Other herbicides as pre-planting soil-incorporated or premergence treatments to control broadleaved and grass-type weeds plus 2,4-D to prevent witchweed seed production have been highly effective combinations for witchweed control. Quick eradication of witchweed will not be easy but effective control now and future eradication look favorable.

Type
Research Article
Information
Weeds , Volume 10 , Issue 3 , July 1962 , pp. 182 - 192
Copyright
Copyright © 1962 Weed Science Society of America 

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References

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