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Cottonseed Oil Helps Malathion Fight Boll Weevils

By Tara Weaver-Missick
June 30, 2000

Adding refined cottonseed oil to malathion sprays makes them more effective at controlling boll weevils in cotton fields, Agricultural Research Service scientists have found.

The boll weevil has been a “hole in the pocket” for southern cotton farmers, causing billions of dollars in damage, crop losses and control costs since entering the United States in the late 19th century. For this reason, the U.S. Department of Agriculture started the Boll Weevil Eradication Program in 1978 to help farmers battle this pest.

The first year of the program begins in a particular area in August and continues into October. During this time, growers spray 8 to 12 applications of malathion to reduce the number of weevils entering diapause--the dormant period in the pest’s life cycle.

To reduce malathion application costs for boll weevil eradication, researchers with the ARS Application and Production Technology Research Unit in Stoneville, Miss., evaluated different oil mixturesfor their ability to enhance the effectiveness of malathion.

They found that, during July, boll weevil mortality from an 8-ounce mixture of malathion and cottonseed oil was the same as from a 10-ounce application of undiluted malathion for the first 2 days after application. In August, however, there were no differences in mortality until 5 days after application.

Their research also showed that malathion accumulates on the surface of mature cotton plants after repeated application during rain-free periods in August. The researchers say this implies that the interval between applications during this part of the growing season could be increased, thus reducing the number of applications and the cost of eradication.

The 8-ounce mixture of malathion/cottonseed oil is 20 cents per acre per application cheaper than a 10-ounce application of malathion--a substantial reduction.

Scientific contact: Joseph E. Mulrooney, ARS Application and Production Technology Research Unit, Stoneville, Miss.; phone (662) 686-5342, fax (662) 686-5372,