First thing- Crab grass or another crappy looking grass?
The time of year tells us a lot about what you are most likely looking at. Crabgrass is a summer ANNUAL and Quack grass, Tall Fescue and Nimblewill are PERENNIAL grassy weeds. In the spring, until about mid to late June, you’re most likely looking at either Quackgrass or Tall Fescue. (Note: there are other grassy weeds with biannual and perennial life cycles.) Nimblewill (Muhlenbergia schreberi ) is also a perennial grass that greens up a few weeks later and goes dormant early in the fall but still will be actively growing by April/May many weeks to months before crabgrass is up. Quackgrass (Elymus repens), Tall Fescue (Festuca arundinacea) and Nimblewill are common problem perennials, meaning that once they get into a lawn, they come up every year, like the perennial Bluegrass, Ryegrass, and Fine Fescue that make up your cool season turf. In fact, Quackgrass is very easily spread through seeds or just little bits of roots. Because these grasses are cool season perennials in a cool season perennial grass lawn, there are limited options in the applicators tool box.
Turf Type Tall Fescue has been bred to look more like Blue grass and is found in some seed mixtures, but can start showing some of the original more native properties that clump, becoming an eye sore in an otherwise uniformly colored and textured lawn, which is not appealing. There is no easy way to get rid of them without some short term kill spots or thinning. It takes special methods that are not part of the regular program. Our Tall Fescue Control treatment or Our Nimblewill Control can selectively kill it, without killing the Bluegrass. The Quackgrass, however, is only controllable by using a post-emergent, non-selective vegetation control (similar to Round Up) and then seeding the killed area. Please let us know if you would like to talk about your options. If you would like to go over your grasses and identify what you have, just let us know. Or you can contact the state extension office.
- Learn more about Perennial Grassy Weeds in Lawns University of Illinois Extension
Crab Grass (Digitaria)
- Summer Annual germinates from seeds once a year once soil temperatures are above 55 consecutively for 7-10 days
- Usually germinates as early as late May or June in Northern IL.
- Full sun open areas
- Preventive control is best, but post emergent options are available while it's young, until it's mature 6/8+ tillers like the picture of mature Crab Grass
- First frost kills the plants, but the seeds remain dormant through the winter, ready for favorable soil temps.
- In severe early infestations Crab grass can choke out patches of lawn grasses.
- Lawns mowed 2½ inches or higher tend to have less problems with annual grasses like crabgrass
Annual Grassy weeds like Crabgrass can cause problems in many Lawns and can be treated through Integrated pest management (a combination of chemical and non-chemical practices). encouraging a dense stand of vigorously growing ornamental grasses is the best way to prevent weeds including crabgrass from invading. Mowing height has a big impact because Lawns mowed 2½ inches or higher tend to have less problems with annual grasses like crabgrass. Close-mowed lawns are more open to the sun with more direct sunlight warming the soil, even shining down the cracks in the soil allowing more crabgrass seed to germinate and proliferate. Studies confirm crabgrass seed can germinate over a hundred years later, so yes the sun shining down cracks in the lawn finding seed already in your soil just waiting for favorable conditions or maybe it found its way in on the mulch or even the wind. The first frost kills the plants, but the seeds remain dormant through the winter. When the ground temperature warms up, the seeds begin to grow. Open bare soil is ideal for crabgrass whether preventive chemicals were applied or not. To keep crabgrass out of a lawn it must first have a lawn grass covering the soil in partnership with a pre-emergent treatment that can keep bare soil weed free. Light, frequent watering favors crabgrass, the opposite of proper watering practices (Heavy infrequent watering). Crabgrass often invades areas seeded in late spring because of bare soil, frequent watering, and the onset of hot weather - all ideal for its growth. Weed Control treatments (weed Killer/Herbicides) are available to manage annual weeds and in combination with proper mowing height, good control is usually achieved. Pre-emergent herbicides prevent annual grassy weeds like crabgrass from emerging and completing its germination cycle and growing. Some products can treat preventively and post emergently so some products can be applied right up to and through the very germination and the first few growing leaf blades (tillers) . Applying pre-emergent herbicides are ideally applied before crabgrass starts germinating/growing. Crabgrass will germinate when soil temperatures are above 55 to 60F° for 7-10 consecutive days, and will continue germinating as the soil gets warmer also many other annual grasses germinate at 60 degrees and higher. In Northern Illinois Pre-emergent crabgrass herbicide should be applied by early to mid-May and if the spring is colder, such in a late spring, this treatment can be put down through May. The best way to avoid crabgrass is to improve the lawn through better cultural practices along with a foundational Lawn care program with pre-emergent applied in the spring. Until the conditions that promote crabgrass are corrected, crabgrass and other weeds in the lawn will continue to thrive. Using cultural practices like improving growing conditions with better soil with organic fertilizer/top dressing, core aeration to reduce compaction and work the soil, over-seeding to increase grass density, proper watering/irrigation, and mowing at the proper height, will reduce problems crabgrass as well as other weed problems in a lawn.
Treated lawn, cut less than 2" at top of ditch facing sun
Even with a Pre-emergent treatment to block Crabgrass, It needs a thick lawn shading, the soil and sun work in partnership.
Lots of Crabgrass- Untreated lawn cut less than 2 inches
More Crabgrass on left sun facing side to south sun head on, being cut less less than 1.5 inches, perfect combination for a bumper crab grass crop.
