SPRINGFIELD -- Crabgrass is an unwanted lawn invader that gets more attention than any other weed, according to Patrick Byers, horticulture specialist, University of Missouri Extension.
Hot, wet weather brings an explosion of crabgrass. That means this time of year in southwest Missouri, crabgrass also generates lots of phone calls to MU Extension offices from concerned lawn owners who want crabgrass out of their lawns.
There is little you can do to treat it when it reaches the current tiller stage.
"Practices that encourage a healthy, thick turf are the best defenses against crabgrass. But, when turf management practices are not enough, you may need to resort to pre-emergent herbicides and those need to be used in the Ozarks during the spring, no later than April 1," said Byers.
IDENTIFICATION
Crabgrass is an annual grassy weed and is easy to identify. It germinates in the spring and grows well throughout the heat of the summer. Its wide leaf blades, heat tolerance, and prostrate growth habit make it an eyesore in the lawn and allow it to smother desirable turfgrasses. During the summer crabgrass will produce seed heads even at low mowing heights.
Crabgrass plants will be killed by the first hard frost in the fall, and will drop their seed heads.
In the spring, new crabgrass seedlings emerge around the previous year's plants, unless this open space was over-seeded in the fall with a desired turfgrass or a pre-emergent herbicide applied in early spring.
SPRING CRABGRASS PREVENTION
A combined crabgrass preventer and fertilizer saves time with a one-step application and generally a flush of green growth is noticed immediately. But, if preferred, crabgrass preventer can be applied separately; however, it is difficult (and often fruitless) to do any spring seeding after your crabgrass preventer is in place.
Crabgrass will emerge when five consecutive days reach 70 degrees Fahrenheit. Most pre-emergent herbicides will not kill crabgrass that has already emerged. They must be applied and watered in to develop that herbicide barrier before weed seed germination.
"The amount of product needed depends on your lawn's square footage and the product itself. Before purchasing a product, measure your lawn to obtain the accurate square footage to be treated," said Byers.
Crabgrass prevention needs to happen in the spring, before seed germination. In southern Missouri, applications should be down no later than April 1.
Then, preventers typically need one-half inch of water to activate the chemical barrier that prevents crabgrass germination according to Byers.
MORE INFORMATION
See the MU Extension publication "Turfgrass and Weeds" (IPM1009), available for free download at extension.missouri.edu/p/IPM1009 or contact the Master Gardener Hotline, (417) 881-8909, or the nearest MU Extension Center.
General News on 08/24/2016