Effect of Prodiamine and Isoxaben Tank Mixture for Early Postemergence Control of Bittercress

Hairy bittercress (Cardamine hirsuta) is consistently listed as one of the top ten most common and troublesome weeds in container nursery production. Previous research has shown that isoxaben can provide early postemergence control of bittercress before it reaches the flowering stage of growth. Isoxaben + prodiamine tank mixtures are popular among container nursery producers as both of these herbicides can be applied over the top of hundreds of ornamentals and provide a broader spectrum of weed control when combined. Research was conducted to determine if early postemergence control of bittercress is reduced when prodiamine is tank-mixed with isoxaben. Bittercress seed (0.1 g) were surface sown onto 7.6 cm pots filled with standard nursery growing media and fertilizer amendments at two separate dates in order to have two growth stages including small (seeded on Feb. 24, 2015, approximately 1.8 cm tall) and large (seeded on Feb. 24, 2015, approximately 5 cm tall). Four rates of isoxaben (Gallery^® SC) (0.14, 0.28, 0.56, and 1.1 kg ai/ha) and two rates of prodiamine (Barricade^®) (0.8 and 1.7 kg ai/ha) were applied alone and in tank mixtures using all possible combinations. A non-treated control group was also included. Treatments were applied to both growth stages of bittercress on March 11, 2015 using a standard pressurized sprayer on an outdoor container pad. Plants received overhead irrigation (0.6 cm) 1 hr after treatment, were allowed to dry and then moved into a shaded greenhouse for the remainder of the trial. Bittercress control was assessed by taking visual control ratings at 1, 2, and 4 weeks after treatment (WAT) and fresh weights were determined at 4 WAT. Results showed that when applied alone, prodiamine only slightly reduced bittercress fresh weights when compared to the non-treated control. For both stages of growth, bittercress control increased with increasing rate of isoxaben and bittercress was completely controlled at the two highest rates. No antagonistic effects were noted across any isoxaben rate when prodiamine was added. While the best weed control will be achieved when preemergence herbicides are applied to weed free pots, results from this study indicate that isoxaben will continue to provide early postemergence control of bittercress when used in a tank mixture with prodiamine.