Use Preemergent Herbicides Now to Prevent Crabgrass and Other Summer Weeds

Use Preemergent Herbicides Now to Prevent Crabgrass

Brian Jervis: Ask a Master Gardener

Sunday, February 18, 2018

Q: When should I use crabgrass preventer on the lawn? And what is suggested to use? Steve C., Tulsa

A: There are several approaches one may take concerning lawn weeds. Some people simply ignore them, while others will wish to eliminate or prevent weed growth. The most effective preventative measure is to cultivate a healthy, thick lawn, which prevents weed seed germination and crowds out existing weeds. Any additional measure you may take toward a weed-free lawn, whether it is Bermuda or fescue, includes herbicides.

Herbicides for lawns come in two categories: pre-emergent and post-emergent. The pre-emergents are applied before the weed germinates; the post-emergents are used after the weed is growing. Pre-emergents should be applied to the lawn in February or no later than March 15 to prevent crabgrass and other summer weed growth. Pre-emergents for control of winter weeds should be applied in late August up to mid-September.

Always apply according to label instructions. When applied correctly, they are effective but still may not provide 100 percent control of all crabgrass. Activation requires all products to be watered into the lawn. Watering causes the soil surface to be coated with a thin layer of the herbicide and, because they dissolve poorly in water, may last for several weeks.

Some of the more popular herbicides that you will find in the Tulsa area are (brand names with the generic names in parenthesis): Amaze (benefin+oryzalin), Balan (benefin), Barricade (prodiamine), Hi-Yield Crabgrass Control (benefin + trifluralin), Dimension (dithiopyr), Halts (pendimethalin) and Portrait (isoxaben).

Generally, the products with benefin, alone or in combination with trifluralin, have a shorter duration of activity. A second application may be needed again in 10-12 weeks for control of late germinating crabgrass and goosegrass. Barricade, Dimension and Halts all have a much longer period of control of crabgrass and may need no second application. However, if allowed on the label, a second application can be an insurance policy that is to be applied no later than the second week of May in the Tulsa area.

All of these products, except Portrait, are excellent in preventing crabgrass growth and will have some effect on controlling broad leaf weeds from seed as well. The types of broadleaf weeds controlled vary by product. Dimension, Barricade and Halts all have good activity in preventing broadleaf weeds. Portrait is unique because it is formulated for broadleaf weed control alone and has little to no effect on crabgrass.

Whatever your choice, if you do use a pre-emergent, February/March and August/September are the times for application. However, do NOT use in late summer if you plan on reseeding fescue in the fall. Pre-emergents may be used on all Tulsa lawn grasses.

If you have questions about these products or lawn care in general, the OSU Cooperative Extension has two excellent condensed information sheets on Bermuda and fescue grasses. They are available for free at the Tulsa Master Gardeners website (tulsamastergardeners.org, under “Lawn & Garden Help”, then “Turfgrass”), as well as at the OSU Extension Office, 4116 E. 15th St. near the Tulsa Fairgrounds.

Garden tips

• Mid-February is a good time to begin pruning and fertilizing trees and small fruits.
• February is a good time to begin cutting back your perennial ornamental grasses, such as Pampas grass. Cut back to remove the dead grass, but avoid damaging new buds and early green growth at the base.
• Begin planting blackberries, raspberries, strawberries, grapes, asparagus and other perennial garden crops this month. Contact Tulsa Master Gardeners at 918-746-3701 for specifics about these plants.