Greenhouse studies were conducted to determine the response of velvetleaf, common cocklebur, and ivyleaf morningglory to mesotrione and atrazine applied PRE, and to characterize the nature of any interaction between mesotrione and atrazine. Sensitivity to mesotrione was as follows: velvetleaf > common cocklebur > ivyleaf morningglory. Sensitivity to atrazine was as follows: ivyleaf morningglory > common cocklebur > velvetleaf. Combinations of mesotrione and atrazine resulted in at least an additive interaction. The activity of mesotrione and atrazine applied in combination was generally additive for control of velvetleaf and ivyleaf morningglory but was synergistic for several rate combinations.
Nomenclature: Atrazine, mesotrione, common cocklebur, Xanthium strumarium L. #3 XANST, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE, velvetleaf, Abutilon theophrasti Medicus # ABUTH.
Additional index words: Synergism, additive, herbicide interaction.
Abbreviations: DAT, days after treatment; GR50, rate causing 50% growth reduction; HPPD, 4-hydroxyphenylpyruvate dioxygenase; LDR, Logistic Dose Response equation.
