PreEmergent for Cheat grass
I would like to know the best time of year to put out Preen, the preemergent herbicide I purchased to help control cheat grass in my yard. I have tried pulling it by hand but the cheat grass has gotten too far ahead of me. I expect to put out the Preen in the fall and again in the spring to get a good control on cheat grass, but I don't know if I should wait as late in the fall as possible or get it out soon, in late summer. Any recommendations are appreciated.
Deschutes County Oregon
There is a section on the Preen label called "When to apply Preen Garden Weed Preventer". In this section it tells the user to apply the product before weeds get a chance to germinate. It also tells you that it should be reapplied every 9-12 weeks.
The cheatgrass in our area generally starts to emerge in September or October, sporadically during the winter on warm days and then goes gang-busters March through April ( a general time line). Using this information one should put out the Preen around the middle of September and then in mid March but only if the ground is thawed and will accept water to carry the preen into the soil. If the ground is frozen it will not take in the preen and it will just wash off and likely go to an area that it was not intended.
If the ground thaws out enough to take in the preen in late February it would also be a good time to apply the preen but only if the ground is thawed an inch or two.