Treatments were applied with a CO 2 -pressurized backpack sprayer calibrated to deliver 20 gpa at 30 psi. All treatments contained Sylgard 309, a silicone surfactant. Silicone surfactants are not recommended with some herbicides and using it may have reduced control with some herbicides. Hoary cress control was evaluated in 1997 and then a year later on May 7 and August 14, 1998. Although the hoary cress population was consistent throughout the plot area at the time the treatments were applied in 1997, evaluations of the herbicide treatments in 1998 were variable.
Some variability arises from the differences in growth stage at the time of application.
Also with such a dense canopy, larger plants may intercept the majority of the herbicide spray reducing the amount that is received by plants within the canopy. Control was poorest with Banvel and Tordon alone. Treatments will be evaluated again in 1999 to determine how long hoary cress control is maintained by each treatment. Additional research also needs to be done to identify the most effective application time for the herbicides that worked well in this trial. Hoary cress control with postemergence herbicide applications, Malheur Experiment Station, Ontario, Oregon, 1998.