BP-10-12
weed science
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • DEPARTMENT OF BOTANY AND PLANT PATHOLOGY LILLY HALL OF LIFE SCIENCES • WEST LAFAYETTE, INDIANA 47907

FACTORS TO CONSIDER WHEN PURCHASING ADJUVANTS FOR USE WITH HERBICIDES
T. N. Jordan, Extension Weed Specialist

Adjuvants (surfactants and crop oils) are used with herbicides to increase the wet-tability of spray solutions to obtain better coverage and increased penetration of the spray solution into the plant. By getting more of the herbicide into the plant, you essentially increase the activity of the herbicide; this is the reason for adding an adjuvant to a herbicide solution.
Manufacturers of herbicides use many different adjuvants in formulating the product, These adjuvants are added to stabilize the pure chemical in the formulation sold to the farmer. Qn-farm use of adjuvants should be only for increased wetting and pen-etration of foliar herbicides. Contact herbicides such as Paraquat and dinitro (DNBP) need an adjuvant to help moisten foliage and increase herbicide coverage and penetration for maximum weed control. This is also true for residual herbicides such as Lorox and atrazine when used as a postemergence application. Even translocatable herbicides like 2,4-D, Banvel, and dalapon, can be more effective when applied with an adjuvant.
Label restrictions prohibit the use of adju-vants with certain applications; thus, the herbicide label should be consulted before an adjuvant is added to a herbicide solution.

Adjuvants are marketed under many different trade names. These may be products from parent chemical companies and marketed under trade names such as X-77, Surfactant WK, Cittowett Plus, or these may be products owned by co-ops and distributors who have bought from parent companies and use their own trade names. Most crop oils are sold as a crop oil concentrate. This is usually a mixture of 80 percent crop oil plus 20 percent surfactant. Crop oils are usually preferred over surfactants, especially in corn, because they not only penetrate and spread the herbicide solution, but they also keep the foliage moist longer than do surfactants. Crop oils are usually added to the spray solution at the rate of 1 to 2 gallons per acre and crop oil concentrate at 1 to 2 quarts per acre, whereas surfactants are usually recommended as a percentage of the volume of spray being applied (1/4 to 1/2% by volume). If 20 gallons of spray solutions were being applied per acre, then 1 gallon of surfactant would be used on 10 to 20 acres. The recommendation of 1/4 to 1/2% by volume surfactant is based on the use of surfactants that have 85 percent (+ 10%) active surfactant in the formulation. Surfactants with lower levels of activity may have

Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture Cooperating. H.G. Diesslin Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30,1914. It is the policy of the Cooperative Extension Service of Purdue University persons shall have equal opportunity and access to its programs and facilities without regard to race, religion, color, sex or national origin.