First Call: Pre-emergent Weedkillers

That awful cold just a week ago certainly did nothing to speed up application dates for pre-emergent weed control products. Still, warm weather earlier this week helped start up the engines of Spring, so here are the relevant details.

Before I begin, though, I have to say that this is a topic that confuses gardeners more than any other topic in gardening. Let’s begin with the basics.

Defining “pre-emergent”
This is a weedkiller (usually granular) that is applied before weed seeds emerge, that is, before they germinate. Once you can see the actual plant growing, you’ve blown it.

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What weeds will they control?
Because they attack seeds before they sprout, pre-emergent granules are primarily intended for use on annual weeds that complete their life cycle within one growing season. They do not help with perennial weeds that come back from their root systems (nutsedge, Johnsongrass, dallisgrass, etc.).

What are the common pre-emergents?
Products in the consumer marketplace are Dimension (most commonly at independent retail garden centers), Weed-EX with Halts (at national chains) and Balan (often sold in farm supply centers).

All three of those (and other less common types) are primarily intended to prevent germination of grassy weeds.

Gallery is sold in independent retail garden centers primarily to prevent germination of broadleafed weeds (non-grasses).

When should a pre-emergent be applied?
Before the weed seeds start to sprout. It’s better to be a week too early than a day too late.

For summer weeds such as grassburs (sandburs) and crabgrass: 2 to 3 weeks before the average date of the last killing freeze for your area. In South Texas that would be late February. You are in good shape time-wise thanks to last week’s cold. In Central and North Central Texas it would be the first two weeks of March. In North Texas it would be the middle two weeks of March. In the Panhandle it would be late March.

Because these granules are effective for about 100 days you will need to reapply three months later as a “booster shot.” Mark the calendar so you won’t forget. Without this second application the weeds will still germinate later in the season. That second application should be late May in South Texas, early June in Central and North Central Texas, mid-June in North Texas and into the Panhandle.

Note: Buy the product for this second application now, while the stores are fully stocked. Many stores sell out after March and early April and will not have it for this second round.

Gallery is not as critical for summer lawns. Fewer broadleafed weeds are common in hot weather, plus our warm-season grasses tend to crowd them out.

For winter weeds (the ones you can see in your lawn in February and March), apply one of the grassy pre-emergents as well as Gallery the last week of August or the first week of September over most of the state. This timing could be mid-September in South Texas.

What about weed-and-feed applications?
I’m personally not a fan of these combination products. There is too much danger of damage being done to desirable trees, plus the timing doesn’t match up.

Late February and early March would be prime time for the first application of pre-emergent herbicide, but it’s too early to fertilize turfgrass. These two procedures should be done independently.

Posted by Neil Sperry
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