Response of downy brome (Bromus tectorum) and Kentucky bluegrass (Poa pratensis) to applications of primisulfuron

Greenhouse and growth chamber experiments were conducted to evaluate primis ulfuron phytotoxicity to downy brome (Bromus tectorum) and Kentucky bluegra ss (Poa pratensis) as a function of herbicide placement, adjuvants, and env ironmental conditions. Primisulfuron rates needed to produce GR(50) (50% gr owth reduction) values were 0.97 +/- 0.57 and 8.07 +/- 1.85 g/ha for downy brome and Kentucky bluegrass, respectively. Primisulfuron was applied to do wny brome and Kentucky bluegrass at three placement sites: foliar, soil, an d foliar plus soil. Foliar or foliar plus soil applications were more effec tive at reducing downy brome dry weights than the soil application of primi sulfuron, whereas Kentucky bluegrass was injured more from the soil or foli ar plus soil applications than from the foliar application of primisulfuron . Primisulfuron at 5 g/ha applied alone reduced downy brome dry weights by 5%, whereas when an adjuvant was added, dry weights were reduced by 52 to 8 3%. Primisulfuron was more phytotoxic to downy brome at alternating tempera tures of 8 to 16 C and 16 to 24 C than at 0 to 8 C,. Phytotoxicity of primi sulfuron was less when downy brome plants were stressed for soil moisture a fter herbicide treatments than when the plants were not stressed or only st ressed before treatment.