Pre-emergent Time is Here

This past Sunday evening it finally got to me. I’d opened up my Q&A newspaper columns. I’d done five hours of live radio. I’d been to church and talked with friends. And, I’d been working through questions on Facebook. Even though it had been below freezing just two days earlier, the coyotes were howling that same familiar tune: “Is it time for pre-emergent weedkillers?”

Grassburs as they appear in mid-summer on left. Crabgrass as it appears in late spring just as it comes into first flower on right. Both can be prevented with a pre-emergent herbicide applied soon and repeated 90 days later.

I relented and put up the following Facebook post. As of distribution time for this week’s e-gardens, it’s been viewed by more than 45,000 people. I worked hard to get my wording right, so I decided just to repost it for you here in e-gardens. I’ve inserted several Notes to make certain it is exactly accurate for tonight’s (Feb. 20) e-gardens. I’ll put them in green.

Continued Below

From my Facebook page last Sunday evening…
Garden Tip: I’m already getting repetitive questions about pre-emergent weed killers. I’ll go ahead and address it all now.

Temperatures just two days ago were extremely cold in much of the state. Soil temperatures are still cold in the northern half of the state. (Note: Remember that I wrote this last Sunday evening.)

If you are in the southern third of Texas, go ahead and apply pre-emergent weedkiller granules now to prevent germination of summertime grassy weeds such as crabgrass and grassburs.

In the central half of the state (running east and west) wait another 10 to 15 days. (Note: So that would mean somewhere Feb. 25-Mar. 10.)

In far North Texas wait until mid- or late March.

I purposely did not give specific geographic boundaries to those areas because I’ve found that people take them so literally. By “southern third” I’m basically thinking of south of I-10, but there are people on the north side of I-10 who would take that to mean that directly across the freeway they should wait two weeks. It’s not that specific, and as I always have said, it’s better to be a few days early than a day too late. Once these weeds germinate and start growing the pre-emergent weedkillers will not work on them.

There are several good pre-emergents on the market including Dimension, Halts and Balan. These are sold as granules. I am NOT an advocate of “weed-and-feed” products because you are many weeks too early to be fertilizing your lawn.

You will need a follow-up application of pre-emergent herbicide 90 days after the first treatment to ensure a full growing season of prevention. Texas has a very long growing season, and one treatment alone will not be sufficient. Be forewarned that many stores do not continue to stock pre-emergents after the first round. Stock up for two additional treatments.

Finally, for those who ask, “But I can already see the weedy grasses. Isn’t it too late?” My answer is that what you’re seeing now are the winter (cool-season) weeds. They germinated in September and October, and for them you should have applied the same materials between August 25 and September 5. The grasses you’re seeing now will not be crabgrass of grassburs – they’re most likely annual bluegrass (Poa annua), rescuegrass or ryegrass.

(Note: Several insisted they already had crabgrass or grassburs. I would almost guarantee that they’re mistaking rescuegrass for the other, warm-season weeds.)

For non-grassy weeds in your lawn such as dichondra, chickweed, oxalis and clover, you can apply a broadleafed weedkiller spray containing 2,4-D to eliminate them. Read and follow label directions for best results.

(Note: One person posted about corn gluten meal so I’ll address it here. I am not an advocate. Although it was developed at a very respected Land Grant university (“ag school”), Iowa State, no southern universities have research showing it to be effective in controlling crabgrass and grassburs. It is expensive, short-lived and not highly efficient. For what it’s worth, I will not accept advertising for it.)

Posted by Neil Sperry
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