Hello Tim –
AgraLawn Crabgrass Killer is an all-natural, organic weed control used as a spot-treatment in lawns and landscaped areas. To apply, simply wet the area you want to treat with a hose or use immediately after a rain. The product will turn from a white to a bright yellow to indicate adequate moisture when applied. A light to medium dusting applied in even strokes will work best (Do NOT wash the product off of the leaves). Results will be seen in 3-5 days.
Crabgrass Killer can be applied any time of year and is not temperature sensitive. In all of our years of testing it has worked in all temperatures common to North America. Also, your use of the ORTHO product will not impact the efficacy of this product. Killing crab grass has never been easier.
Hope this helps!