Fred from San Jose California writes
I have a landscape company in San Jose California
Pre-emergents would be applied before soil temperatures reach 55 degrees as that is when crabgrass starts to germinate and you have to apply these types of products before the target weeds do so. There is not time restriction between using a post and pre and some are applied together if you have weeds at the same time you need to prevent others but a pre should be applied before a post to prevent in the first place. We do have general lawn care schedules here that can help. The best pre-emergent for crabgrass is anything that contains Dithiopyr as it also has very early post emergent control of crabgrass only if you do not get it down in time and it pops up. Once weeds have emerged you can use a product like Q4 for cool season turf applied when target weeds are actively growing as they only kill those weeds that are sprayed directly. Those please note: For use in California: Biotypes of large and smooth crabgrass in California have shown varied response to this product. If control failure occurs following a full or split application, DO NOT reapply this product. Change to a herbicide with a different mode of action. Tenacity would be an option if you do have this issue.
Answer last updated on: 01/30/2020
