Apply pre-emergents now … or wish you had by the spring

There’s a bit of hocus-pocus in this pre-emergent weedkiller thing. You apply the granules to prevent germination of weeds you can’t even see (yet). That’s why it’s called a pre-emergent product. You put it out before the weeds emerge from their seeds.

Many types of plants sprout in the spring. That includes most of our garden flowers and vegetables, and it also includes lawn weeds like crabgrass and grassburs. Those weeds grow in the late spring and summer, and we call them “warm-season” weeds.

Then there is another category of weeds we see in the winter and early spring. They’re the “cool-season” weeds, and they sprout in early fall. About now! As soon as the first cold front drops night temperatures down near 60F, especially if it’s accompanied by rain or irrigation. That’s when winter weeds like annual ryegrass, rescuegrass, and annual bluegrass (Poa annua) sprout and start to grow.

When you think about it, they operate on the same schedule as most of our spring wildflowers like bluebonnets. They germinate in the fall, establish roots over the winter, and bloom in the spring.

Cool-season broadleafed weeds function on that same schedule, and that list includes clover, dandelions, henbit, chickweed, and others. They are handled separately, and there’s a special notation for them that you’ll want to remember. More on that in a moment.

Preventing cool-season grassy weeds…
• Keep your turf healthy and vigorous and it will crowd out many or most of these invaders.
• Prevent or limit germination of annual ryegrass, rescuegrass (also an annual), and annual bluegrass (Poa annua) by applying either Dimension or Pendimethalin granules. Note: There is no second chance – there is no post-emergent (after germination) product that will kill these weeds without doing harm to your permanent turf. These products will not harm trees or shrubs, and they are safe on any type of permanent turf as long as it’s been through at least one winter.
• Timing of application: Prior to first 60F night.
For the Texas Panhandle that would be Aug. 25-Sept. 8.
For Central two-thirds of the state Sept. 5-15.
For South Texas Sept. 10-20. Water moderately after application.

• Regarding annual bluegrass, southern ag universities and turf authorities have observed that Poa annua has been building up resistance to pre-emergent herbicides. That means you may not get complete prevention of the weed. You should, however, see significant reduction in its population – enough so to justify application.

Dealing with cool-season broadleafed weeds…
So, what do you do with the other weeds? Dandelions, henbit, chickweed, clover, plantain? These weeds can become big and obnoxious.
• Again, you take the best possible care of your lawn. Healthy turf discourages weeds.
• The pre-emergent product Gallery will greatly reduce germination rate of all these broadleafed weeds if it’s applied before they start to sprout.
• Schedule of application will be the same as above for grassy weeds and their pre-emergent granules.
• If you choose to use Gallery pre-emergent granules, apply the grassy pre-emergent granules first, then the Gallery granules, then water both across the lawn surface with one single watering.
• Gallery can be expensive if you have a large area to cover. You do get a second chance with this category. You could wait until they germinate, then apply a broadleafed herbicide spray (containing 2,4-D) to eliminate all the young seedlings. That spray would be made sometime in the second half of November.