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Urea adducts (urea clathrates) of high molecular weight ethoxylated linear fatty alcohols at low doses are very effective enhancers of sulfonylurea herbicide biological activity. Greenhouse and field trials have identified the preferred alkyl chain length and the degree of ethoxylation for maximum biological efficacy with a broad range of sulfonylurea herbicides at low adjuvant doses. Based on experimental data, the optimum fatty alcohol surfactants include a C16–18 hydrophobe with 25 moles of ethoxylation or a C24 hydrophobe with 13 moles of ethoxylation. However, the latter alcohol ethoxylate is not readily soluble in water while the former dissolves slowly and forms gel phases when mixed into cold water. These characteristics make them generally unsuitable for use as unformulated materials. One readily cold water soluble and commercially available form of this surfactant type which presents very similar performance is based on a C18 linear alcohol ethoxylate with 20 moles of ethoxylation, BRIJ® 78. This ethoxylated linear fatty alcohol remains effective after admixture with related nonionic surfactants and transformation into a readily soluble solid form identified as the urea clathrate of the surfactant.
Urea clathrates can contain between 40–60% of nonionic surfactant by weight while remaining free flowing with melting points above 80 °C. As a result, they can be used as tank-mix or combined with the dry sulfonylurea herbicide formulation. Because of the high activity at low doses, a concentrated dry sulfonylurea herbicide formulation can be achieved with a specific urea clathrate ATPLUS® UCL 1007. Such a combination potentially offers the user more convenience, lower chemical volumes, and reduced costs.
adjuvant, clathrate urea, surfactant, sulfonylurea, urea, water dispersible granules
Development associate, Uniqema, New Castle, DE
Biological program leader for Adjuvants, DuPont Crop Protection, Stine-Haskell Research Center, Newark, DE