Summers in Iowa can be hard on our lawns. The days are long, so sunlight is drying out our landscapes for over 12 hours a day. The weather is hot and humid, weakening the turf and making it susceptible to various insects and diseases. Summer also brings about annual grasses, and the one that gets the most attention in this part of the country is crabgrass. Crabgrass is considered a “warm-season grass”, meaning that it won’t germinate until late spring, and thrives in the hottest weather. Unfortunately, this time of year is hardest on the grasses we want to keep strong (these are considered “cool-season grasses”), so crabgrass is able to compete and take advantage of these conditions. We’ll take a look at how to identify crabgrass, and what can be done to control it.
Identifying Crabgrass in Your Yard
Crabgrass generally has a lighter green color, but it does tend to darken as it matures. Crabgrass has a broad leaf that has a soft texture, and it grows low to the ground. It starts as single leaf, then over time develops tillers, which are new stems that arise from the parent plant. As more tillers develop, the plant flattens out and gets a more rounded appearance. As it matures even more, above-ground stems called stolons are produced. These stolons grow along the soil surface and will take root, forming an entirely new plant. Below are some pictures showing a crabgrass plant as it matures.
Because of its growth habit, crabgrass can withstand regular mowing and grows outward more than upward. Crabgrass is unaffected by drought, and will thrive and spread while the lawns may be suffering. After reaching maturity, seedheads are produced and that seed is dropped onto the soil or spready via mowers, wind, birds, etc. If conditions are right, that seed will germinate the following spring/summer. With crabgrass being a “warm-season” grass, it doesn’t like any semblance of colder temperatures. The first frost of the year sends crabgrass into dormancy. It will turn purple, then brown, and eventually “melt” away. While it is great to see crabgrass die off, it’s an empty victory if it was able to produce seeds. With each plant producing hundreds, if not thousands, of seeds it’s easy to see how things can get out of control.
Fighting (and Killing) Your Lawn's Crabgrass
Whenever we encounter weeds, we have two treatment options: post-emergent and pre-emergent. Early-season lawn applications should ALWAYS include pre-emergent for crabgrass. The cost for fertilizer to include pre-emergent herbicide is minimal, and if it’s 90% effective, it’s money well spent. UltraLawn’s full program includes crabgrass pre-emergent on our first two visits of the season. In order to achieve season-long control, this method is recommended. Over the years, its been found that sequential applications are needed in order to get the product into the soil early enough to knock back our first “wave” of weeds, and again to make sure control extends late enough into the summer. When these pre-emergent herbicides are in the soil, it creates a toxic environment for weeds that are trying to germinate.
Crabgrass pre-emergent will be effective right away in its first season, but it usually takes a few years of a consistent program to reach a point where a Cedar Rapids or Iowa City homeowner can boast of a lawn that is 100% crabgrass free.
There can be breakthrough in certain spots even if pre-emergent has been used for years. When we see crabgrass, it is usually along the edges of sidewalks and curbs. Those areas get very hot due to the proximity to pavement, and are also exposed to sand and salt from winter snow removal. That heat makes the product break down a little bit faster and leads to a bit of breakthrough.
Post-emergent control of crabgrass can be achieved with several products. Our mid-summer application is a granular fertilizer with optional grub control, followed by a thorough walk through the lawn to spot-treat weeds, crabgrass included. On lawns that have received pre-emergent weed control, very little time is spent treating crabgrass. If a lawn has NOT received pre-emergent weed control, much more time and effort will be spent trying to catch up. In some cases, an infestation is so bad that spraying everything would leave much more bare ground than is tolerable. It may be better to let the crabgrass go dormant naturally in the fall, which will allow the turf to fill in where it can. It will be imperative then to make sure pre-emergent is applied the very next spring.
As always, maintaining a healthy stand of turf through proper fertilization and mowing will go a long ways in preventing crabgrass infestation. We often see weeds when a lawn is mowed too short. Low mowing heights put undue stress on the plant, causing it to thin out. This creates room for weeds to germinate. What also happens is that low mowing heights eliminate too much leaf tissue. That leaf tissue acts as an umbrella, preventing sunlight from hitting the soil. With that umbrella gone, weed seeds are more likely to germinate.