Question of the Week #2: February 2, 2017

 

“Neil, I’m seeing weeds and grasses popping up all over my lawn with the warm weather earlier this week. Is this the time to apply pre-emergent?”

No, it is not the right time to apply pre-emergent herbicides.

People who ask me this question are obviously confused by the types of weedkillers. (Like I’m confused by all the types of TVs!) Let me try to explain in a few simple pointers.

• The term pre-emergent refers to the fact that you must apply it before the weeds “emerge,” that is, germinate. Once you can see the weeds, you’ve basically blown it for that generation of weeds.

• Pre-emergent weedkillers work only on annual weeds that start their life cycles from seed every year. Pre-emergent herbicides will not help, for example, with perennial weeds that come back from their roots.

• There are two categories of annual weeds:
(1) Those that germinate in September and grow in the cooler months. They’re appropriately called “cool-season” weeds.
(2) Those that germinate in spring and early summer and grow in the warmer months of later spring, summer and into early fall. They are called “warm-season” weeds.

 

 

• To be effective, a pre-emergent weedkiller must be applied before the weed seeds start to germinate. For the cool-season weeds (the ones you are seeing now!), that time would be the first week of September. For warm-season weeds (like crabgrass and grassburs), that time comes in early spring. It will vary with where you are in the state, but it’s late February or the first week of March in South Texas into March 5-10 in Central and North Central Texas and March 15-25 in the Panhandle. Because Texas has such a long growing season, you will need to apply a “booster shot” of the same herbicide 90 days (3 months) after the first treatment.

• Annual weeds are also broken into two other categories:
(1) Grassy weeds such as annual bluegrass and rescuegrass in winter and crabgrass and grassburs in summer. Team, Dimension and Halts will prevent these if applied before germination.
(2) Broadleafed weeds – those types that are obviously not grasses, including dandelions, clover, henbit and chickweed. Gallery will prevent these if applied prior to germination.

• If you miss a pre-emergent application and weeds do develop, you can apply a broadleafed weedkiller spray (containing 2,4-D and perhaps other ingredients) according to label directions to control existing non-grassy weeds. Unfortunately, there is no second chance with grassy weeds. We have no post-emergent herbicide that we can use to kill existing grasses without doing serious damage to our permanent lawn grass.