Cut off crabgrass
Amy Jordan, Special to the Gazette
Thursday, March 31, 2011
Many of us have lawns. These lawns vary, often showing the degree of interest or expectations we have for our lawns. I find people fall into three different groups when it comes to lawn care. Those that want a weed-free, deep green, mowed perfectly lawn. Those that think, “If its green, who cares what it is.” And everyone else falls somewhere in between.
Individuals in the second category often welcome crabgrass because it looks kind of like lawn grass and grows in the worst soil with lots of heat and little water. Individuals in the first group do all they can to prevent or eliminate crabgrass from their lawns. Individuals in the last category often address crabgrass if it becomes a problem, but tolerate it in a few places.
Regardless of what your expectations are, lawn care doesn’t have to be expensive or time consuming. A few important cultural practices make a big difference. Mow at the proper height, water deeply and infrequently, reduce compaction, and fertilize at the proper time. More information on all of these practices can be found at www.ksuturf.com.
Crabgrass is rarely a problem in lawns that are dense and mowed at the proper height. This is because crabgrass seed requires contact with the soil and sunlight to grow. Lawns that are dense and mowed appropriately do not have exposed soil, preventing invasion by weeds. Therefore, the most important way to have a lawn with minimal crabgrass (or other weeds for that matter) is to have a healthy lawn and mowed at the upper end of the range for your type of grass. For tall fescue that would be 3 to 3-1/2 inches.
Crabgrass is a warm-season annual weed, so any crabgrass plants you had last year are dead. Crabgrass plants you get this year will be from seed that typically begins germinating around May 1.
Crabgrass preventer is another name for a pre-emergence herbicide. It doesn’t actually “prevent” the seed from germinating but rather the germinating seed takes up the herbicide and is killed. If a lawn had problems with crabgrass last year or there are some thin or bare spots in the yard, these might be a good option. These products must be put down before the seed germinates, and it has little effect on existing crabgrass plants.
April 15 is a good target date to have crabgrass preventers applied. That gives the product time to evenly disperse in the soil by the time the seed germinates. However, because weather varies year to year, a better indicator of proper timing is the blooming of ornamental plants. The Eastern Redbud is a good indicator plant for crabgrass preventers. The trees around here are just beginning to bloom, so now would be a good time to apply the product if you plan to. Some products last about 60 days, so may have to be applied twice (about eight weeks apart) for adequate control.
Exceptions to this are products containing Dimension (dithiopyr) and Barricade (prodiamine). Both of these products have a long residual effect and will provide season-long control, so they can be applied well before mid-April. Dimension can control crabgrass that has germinated when applied at the proper rate, as long as the plants are still small. Dimension is also the best choice if treating a lawn that was planted late last fall. Normally you should not use a pre-emergence herbicide unless the lawn has been mowed two to four times. However, Dimension can be applied as early as two weeks after the first sign of germination. Lawns established in the fall can be safely treated with Dimension this spring even if they have not been mowed.
• Amy Jordan is a horticulturist with K-State Research and Extension in Lyon County.