Two weeks ago I addressed the question of when to apply our crabgrass preventer, which leaves this week open for the question of what product to use. My general response to this question is that there is no single product that is superior to all other products available. All provide excellent crabgrass control when applied properly. The real emphasis needs to be placed on application, not which product is used. Correct timing of the application and uniformly applying the proper amount are probably the most important aspects related to chemical control of crabgrass because if these two aspects aren't performed correctly, then all the preliminary work on deciding what to use was a waste. If not enough herbicide is used, crabgrass control will be unsatisfactory; and if too much herbicide is used, turfgrass injury is likely.
With this application, we will also need to make sure the preemergence herbicide has been moved into the seed germination zone of the soil and not on the soil surface. Most often Mother Nature does this for us, but if the forecast is for dry weather, one will need to irrigate within a couple days after the application.
Almost all preemergence herbicides are to be applied only to established turfgrasses. The only exceptions are products containing DCPA (Dacthal) and siduron (Tupersan). DCPA can be used in the spring following fall sown turfgrass. It can also be used after spring seeding. However, the 60 day delay needed after sowing so that your turfgrass survives often leads to poor crabgrass control. Therefore, if you will be or have spring seeded, use siduron which can be applied at the same time as seeding.
Finally, I would like to stress the cultural practices that one should utilize to help control crabgrass. Establishing and maintaining a dense vigorous growing turfgrass by including such practices as proper mowing, aeration, irrigation and fertilization is the first step towards reducing crabgrass infestations. These cultural practices help to get rid of any openings in the turfgrass which allow the light needed for crabgrass seed germination. These practices also help the turfgrass compete with the weeds. Therefore, your fight against weeds needs to start with good management.
This article originally appeared in the April 28, 1993 issue, pp. , 1993 issue, pp. 55-56.