Better Crabgrass Control
The how to, when and why of proper practices
Although its only the beginning of March as I am putting together this article, the weather outside feels, smells, and sounds more like the first of April. While Michigan never knows what mother nature may have in store for us around the corner,we can try to assume that the excessively mild winter will bring two things; an early spring, and crabgrass germination.
What is Crabgrass?
Crabgrass (Digitaria spp) is a extremely common annual weed with its wide leaf blade, clump characteristics, that infest lawns competing for space with Kentucky Bluegrass, and Fescue mixes as well as other varieties prevalent in the mid Michigan region (Figure 1). It is considered a warm-season annual weed, only reproducing by seed, as all other annuals do as well. Crabgrass can begin to germinate when daytime soil temperatures (not to be confused with air temp alone) are approximately 60º F for 3-5 days at just below ground level (minimum 54 but predominately closer to 70 degrees). Further into the season the weed-grass begins flowering and setting seed usually no later than July. The grass plant then eventually dies with the first frost of fall (typically later September).
Crabgrass has tremendous survival reproductive capabilities. Because of this, it is unrealistic to expect a crabgrass free lawn. You cannot eradicate crabgrass (or any other pest for that matter); a few crabgrass plants in your lawn should be viewed as acceptable.
How do I rid my lawn of this Crabgrass monster
While the best way to kill crabgrass is with pre-emergent herbicides, the most effective way to control crabgrass is to create a dense, healthy turf. A healthy turf will compete well with crabgrass and prevent it from establishing. Following the suggestions below can do wonders to limit the crabgrass population:
- Fertilize more heavily in fall than spring (such as using .5 lbs N per K in the spring vs. 1-1.2 lbs N per K in the fall), using a balanced Fertilization program to promote healthy turf. By fall, frosts will have already killed any crabgrass.
- Don't let bare spots remain uncovered for long, else opportunistic crabgrass will take root. In the fall, fill in those bare spots by over-seeding.
- When irrigating the lawn, water more deeply and less frequently. Crabgrass is a notoriously shallow weed, meaning too frequent watering only aids the weed.
- Mow "high", leaving the lawn grass at a height of 2 1/2"-3". This will allow the lawn grass to "protect its own turf" better, depriving crabgrass seeds of the light they need to germinate.
Often, cultural control alone will not suppress crabgrass satisfactorily, and a pre-emergent herbicide may be needed. This is especially true along curbing, drives, and other hot spots where the grass can become stressed, as well in newer lawns, or lawns that are thin from damage or improper maintenance.
Pre-emergent herbicides can come in either granular or liquid form and kill crabgrass seedlings as they germinate. Think of pre-emergent herbicides as forming an invisible shield across the soil surface that stops emerging crabgrass dead in its tracks. This shield image will serve as a reminder not to practice core aeration on lawns after applying pre-emergent herbicides, since doing so would only "puncture" the shield. Aerate lawns beforehand, or optimally in the fall instead.
As their name suggests, pre-emergent herbicides kill crabgrass at a specific time: before its seedlings emerge. For success in getting rid of crabgrass in this manner, timing is of the essence. Apply preemergent herbicides before germination, but not too far ahead. The earlier that you apply, the sooner it will lose effectiveness. The duration of effective control depends on the type of product, and how heavy of a concentration you apply.
The control could last 2 to 3 months, or longer than 4 months, depending on several factors. So the timing chosen as to when to apply the crabgrass preventer plays a major role in its effectiveness.
Armed with this newly found knowledge and understanding of how to combat the unappealing sights of crabgrass, and how to control its outbreak, we would like to share with you one last resource that we use extensively to gauge the proper timing of the pre-emergent treatments in the spring. Tracking the Michigan State University’s Growing Degree Day GDD Tracker database of measurement sites around the state, we can predict a scientific approach to the optimum timing of our applications so our products have the best possible chance to do the intended job.
So, although it looks like spring may get here sooner than normal this year, be forewarned, if you see the "big chain operations" out even earlier than you might expect, you may want to question their motives & effectiveness. If you have read this article, I believe you now have the tools to understand what parameters, thought processes and data Emerald Outdoor uses before providing our Round One application to our all important clients, so the job gets done responsibly, without waste and on time.
Portions of Data & Material Credited to:
Zac Reicher, Professor and Turfgrass Extension Specialist,
Purdue University Department of Agronomy
Tom Voigt, Associate Professor and Turfgrass Extension
Specialist, University of Illinois Department of Natural
Resources and Environmental Sciences
David Beaulieu, About.com Guide
MSU Turfgrass Science