Remember crabgrass? It was the tough, clumpy, impossible-to-pull grass that took over lawns and flower beds all over northeast Kansas in the heat of last summer. While you were busy trying to keep it under control, it was busy producing thousands of seeds that will germinate soon.
You might be wondering why we even want to control crabgrass if it does such a good job of multiplying itself. To best answer this, think about what purposes lawns serve. Probably most important is the role turfgrasses play in preventing and reducing erosion in large areas. Crabgrass is shallow-rooted and has a shorter growing season than the recommended turfgrasses for this area, so erosion is more likely to occur in areas where crabgrass has taken over.
From an athletic standpoint, crabgrass lacks the cushion provided by perennial grasses.
In areas other than the lawn, crabgrass uses nutrients and water that might otherwise be used by flowers, vegetables, trees, shrubs or other plants that provide their own benefits.
Also, one little clump of crabgrass might be of minor concern, but crabgrass lives to reproduce. According to the University of Rhode Island, one crabgrass plant can produce 150,000 seeds.
There are a few things you can do to get a head start on crabgrass control this year, though, and now is the time to do it. Crabgrass seeds germinate about the same time in the spring that redbud trees are in full bloom. In most years this is around April 15 in the Lawrence area, so a pre-emergent product would need to be applied prior to that. There are both organic and conventional pre-emergent products from which to choose.
Getting your lawn back in shape is just as important as a pre-emergent. (Dense, healthy turf is by far the best way to control lawn weeds.) Core aerate the lawn this month unless it was done in September (the only better time to do it). When the grass greens up and starts growing, mow high. Fescue and bluegrass are healthier and will fill in better when left at least two to three inches tall.
If you plan to irrigate, apply water only deeply and infrequently. Irrigating once a week is enough for most soils. If we get rain, it may need less frequent irrigation. Over-irrigating will only encourage shallow root growth, meaning your turf will just be more stressed when temperatures climb. Overseed bare spots now (prior to April 15) or wait until September.
For pre-emergent crabgrass control, there are a variety of products on the market. In trials at Kansas State University research stations, Dimension (active ingredient dithiopyr) and Barricade (active ingredient prodiamine) consistently provided the best control. Corn gluten meal is an organic alternative. If overseeding, the only product that can be used is Tupersan (active ingredient siduron).
Corn gluten meal, the organic product, is a waste product that was recognized for its weed-and-feed properties in research at Iowa State University in the mid-1980s. It works the same way that conventional products do and is about 10 percent nitrogen by weight. Corn gluten meal works on a cumulative basis — researchers at Iowa State say users can expect a 50 to 60 percent reduction in weeds the first year, with two or three consecutive years of application needed to get the best control. Make sure to get genuine corn gluten meal — there are also a lot of similar but less effective products on the market labeled as corn gluten feed and distillers’ grain.
Always read and follow label directions when applying any pesticide, whether conventional or organic.
Once crabgrass is up, the only ways to get rid of it are pulling, digging, treating with a nonselective conventional or organic herbicide, or covering the plant(s) with black plastic long enough to cook them.