Crabgrass is a problematic plant that won’t harm your children or pets, but can reduce the look of your lawn. Applying a pre-emergent treatment before crabgrass appears in U.S. Department of Agriculture plant hardiness zone 7 will help keep your turf looking its best.
1. Know Your Enemy
Crabgrass (Digitaria spp.) is an aggressive annual weed that appears during the spring months. It continues to grow and spread throughout the area until it dies from frost. The crabgrass seeds overwinter in the soil and begin to germinate when the soil reaches a temperature of 55 degrees Fahrenheit and stays at or above that temperature. Crabgrass can appear just about anywhere, including in turf, gardens, crop fields, roadsides, orchards, ditches, vineyards and pastures.
2. Pre-Emergent Herbicides for Crabgrass
Pre-emergent herbicides containing pendimethalin, oryzalin or trifluralin are available for homeowner use to control crabgrass. These pre-emergent herbicides generally come in granular form and require a drop-type or rotary spreader to apply. Each type of pre-emergent herbicide has specific instructions that you must follow to prevent harm to the area and increase its effectiveness. For example, one brand of pre-emergent herbicide containing pendimethalin as the active ingredient suggests setting the rotary-type spreader to a 2 1/4 setting to treat a 5,000 square foot area.
3. When to Apply Pre-Emergent Herbicides
In USDA zone 7, pre-emergent herbicides should be applied before the crabgrass seeds have germinated. This is typically in mid- to late February. If you cannot apply pre-emergent herbicides during this time, the crabgrass seeds will germinate and post-emergent herbicides will be required to kill the weeds. However, the Missouri Botanical Garden suggests that you shouldn’t try to control crabgrass in late summer or fall since frost will kill the weeds.
4. Corn Gluten Meal and Crabgrass
A byproduct of corn, corn gluten meal is a natural way to control crabgrass before it appears. It poses no harm to humans or pets, according to the University of Minnesota Extension Service. It can be added to a spreader and applied in the same manner as other pre-emergent herbicides. Twelve to 20 pounds of corn gluten meal spread evenly will prevent crabgrass from germinating on about a 1,000-square foot area. Once the corn gluten meal is applied, use a water hose to lightly dampen the area.
5. Prevent Crabgrass
Once you have controlled crabgrass with pre-emergent herbicides, take preventive measures to keep the annoying weed from returning. Prevention involves maintaining a healthy lawn by mowing the grass at the highest recommended height for the species. This shades the soil to help keep weed seeds from germinating. Furthermore, promote deep roots by watering the lawn deeply but infrequently.
6. Warnings and Precautions
When applying herbicides, make sure to wear the proper safety attire, including rubber gloves, goggles, a long-sleeve shirt and long pants. As with any chemical herbicide, always keep children, pets and pregnant or nursing women out of the area when applying. They should be kept out of the area until the herbicide has a chance to settle. If the herbicide comes in contact with eyes or skin, flush with cool water for 15 to 20 minutes. If ingested, contact a poison control center immediately and follow its instructions.
- University of California Statewide Integrated Pest Management Program: Crabgrasses
- Gardens Alive: Does Warm Winter = Early Crabgrass?
- Zone 7 Nursery: Lawns
- Missouri Botanical Garden: Crabgrass Control
- University of California Statewide Integrated Pest Management Program: Crabgrass
- The Scotts Company LLC: Halts Crabgrass Preventer
- University of Minnesota Extension Service: Corn Gluten Meal -- A Natural Pre-Emergence Herbicide
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