Greenhouse studies were conducted to examine the influence of temperature and relative humidity (RH) on the foliar activity of mesotrione on five weed species. Regression analysis was performed allowing for comparison of estimated GR50 (herbicide dose to inhibit growth by 50%) values for each weed response at either temperature (18 or 32 C) or RH level (30 or 85%). Temperature and relative humidity did not influence the response of ivyleaf morningglory, common cocklebur, and velvetleaf to mesotrione markedly. An increase in temperature or relative humidity increased the efficacy of mesotrione on common cocklebur and velvetleaf up to threefold. Conversely, common waterhemp and large crabgrass were six- and sevenfold more susceptible at 18 C than at 32 C, respectively. Common waterhemp and large crabgrass were four- and twofold more susceptible to mesotrione at 85% compared with 30% RH, respectively. The influence of temperature and RH on the efficacy of mesotrione in foliar applications is species dependent and may be an important consideration for field applications.
Nomenclature: Mesotrione, 2-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione; common cocklebur, Xanthium strumarium L. XANST; common waterhemp, Amaranthus rudis Sauer AMATA; large crabgrass, Digitaria sanguinalis L. Scop. DIGSA; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; velvetleaf, Abutilon theophrasti (L.) Medic. ABUTH.