Ask an Expert – Is Crabgrass Making You Crabby? Six Tips to Help

Taun Beddes & JayDee Gunnell

08/11/2020

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Crabgrass

We often label any weedy grass as crabgrass; however, not all of them are crabgrass. For example, if you have weedy grass growing in April and May, it is not crabgrass. Crabgrass seed germinates when soil temperatures are around 55 F, usually after forsythia are done blooming and just before lilacs start. This is the best time to apply pre-emergent herbicides to prevent crabgrass seed from germinating.

 If you missed this window of opportunity and find crabgrass in your yard, you still have a chance to kill it. Consider these tips:

  1. Post-emergent sprays containing quinclorac offer good control for newly germinated crabgrass. Products containing quinclorac include terms like “lawn weed killer plus crabgrass control” or “dandelion and lawn weed killer with crabgrass control.” However, these products must be sprayed in late spring or early summer before temperatures get too hot – it can’t be done now. The crabgrass is too mature, and these sprays could cause unintended damage to ornamental plants. This is due to other active ingredients in these formulations including dicamba and 2,4-D. These chemicals evaporate at temperatures above 85 – 90 F and drift in the wind. Any broadleaf plant they run into is potentially damaged. Dicamba can also be absorbed by roots of desirable plants. The most common indication of 2,4-D or dicamba damage is distorted, curled, twisted leaves and stems on the new growth of plants.
  1. As far as immediate control measures, hand pulling and digging are some of the best options. This should be done before seeds are produced. Smaller plants often do not recover from cultivation. For larger plants, carefully cut seed heads from the plants and throw them away. For areas with bare ground, such as flower beds, the grassy weed can be cultivated, dug or possibly sprayed with a non-selective herbicide containing glyphosate, if practical.
  1. It is especially critical to improve lawn health in heavily infested areas. Keeping turf thick and healthy is one of the best deterrents. Mow at a height of 2.5 – 3 inches. Make sure the area does not have compacted soil. If it does, this can often be remedied by aeration in the spring and fall. Crabgrass is often a sign that an irrigation system is not working properly. Sprinklers in this area will need to be checked and most likely adjusted. 
  1. Fertilize the area in the spring and fall, avoiding mid-summer applications. In some situations, crabgrass will outcompete the lawn because it is better able to use nutrients from fertilizer than grass in the hottest time of the year. If enough lawn grass is still reasonably thick, consider the use of a pre-emergent in the spring to prevent crabgrass germination.
  1. In non-turf areas, hand cultivation in late spring is very helpful. Additionally, 2 to 3 inches of mulch applied on top of the soil will prevent most weed seeds from emerging. There are also some pre-emergent products registered for use in flowerbeds and gardens. However, be cautious about using them where annual flower or vegetables will be seeded, and always follow the label.
  1. Keep in mind that if the lawn is too thin and pre-emergent is applied, new seed or sod cannot be used in the same area. Pre-emergent products often work by preventing proper rooting of newly germinated seeds, and they do not discriminate between desirable and undesirable seeds. If sod is laid, pre-emergent prevents it from rooting. There is up to a full year wait before lawn seed or sod can be laid.

The best way to eliminate crabgrass is to maintain the lawn and garden areas so they prevent crabgrass seeds from germinating. The old adage that “an ounce of prevention is worth a pound of cure” holds true, especially when it comes to weedy grasses. And if all else fails, remember that you won’t be stuck with crabgrass forever – it is an annual that dies with the first hard frost in the fall!

Photo by JayDee Gunnell

By: Taun Beddes, taun.beddes@usu.edu, and JayDee Gunnell, jaydee.gunnell@usu.edu, Utah State University Extension horticulturists