September rains in the Pacific Northwest usually means that we are going to get flushes of downy brome, if the weather stays warm. Downy brome germinates when soil temperature are above 50 degrees. It can be easily controlled exterior to the crop with glyphosate. Although, you might want to add a downy brome sulfonylurea (SU) herbicide for pre-emergence activity like Outrider or Olympus.
Two things to remember with Rotation Restrictions and some rain is needed to activate the herbicides. Read follow the label for rotation restrictions. ,
If you have a moist soil and then no rain downy brome can germinate and go through the herbicide if it is still on the soil surface. Many growers now split their SU downy brome herbicides fall and spring. Remember to use a good water conditioner and surfactant like Full Load Complete from AgraSyst to maximize the glyphosate activity.
Post emergence control of Downy Brome with the Sulfonylurea type herbicides is greatly enhance with adjuvant like Sure UP from Agrasyst. The adjuvant is built specifically for SU herbicides. It increases the solubility of the herbicides thereby making them diffuse toward the leaf surface and into the plant much faster and at a higher concentration. The herbicide works a lot better and you get better downy brome control. Plus it has a specific surfactant blend that makes the herbicide work a lot better on more grass weeds than just adding a normal non-ionic surfactant.