It's just about time to apply a preemergent herbicide to the lawn

By Keith Mickler

County Extension Coordinator

In about another week or two we will be at the window of opportunity to use preemergent herbicides on our lawn for summer weed control. But not every lawn will need a preemergent herbicide this time of year – only those lawns that have a history of summer annual weeds.

Dr. Patrick McCullough, UGA Extension Weed Scientist and I will try to explain the use of preemergent herbicides in our lawn. Keep in mind that Dr. McCullough and I don't have firsthand knowledge of the weeds in your lawn, only you do.

Crabgrass, goosegrass, dallisgrass are by far the most menacing summer lawn weeds we encounter. However, these menacing bad boys can be momentously reduced with the use of preemergent herbicides labeled for home lawns.

Often I get a phone call or three describing how the preemergent herbicide I recommended (and you spent a fortune on) didn't work. Well, I hate to be a smart aleck (actually I don't) but most of the time it's application error. You applied the herbicide after the weeds had already germinated. Duh, preemergent herbicides kill weeds before they show up in the lawn, not after you can see them.

Preemergent herbicides kill certain weeds just as the seeds germinate. When we see the weeds in the lawn, it's too late to use a preemergent herbicide; we now will have to use a post emergent herbicide. Get pre before germination post after germination.

The secret to praiseworthy weed control when using a preemergent herbicide is to apply the herbicide to the lawn before the dreaded summer annual weeds germinate. The universal time for preemergent herbicide application is around February 15 to March 15. Germination can vary from year to year, so applying too early is always better than doing it late.

Preemergent herbicides primarily control summer annual weeds such as crabgrass, goosegrass and spurge. Post emergent herbicides can control these weeds as well, but preemergent treatments offer the following advantages:

·         Since you apply the chemical before the weed seed germinates, most weeds never appear in our lawn.

·         We can get many preemergent herbicides as granular formulations. Granules tend to be easier to apply for most people.

·         Except for herbicides that contain atrazine, most ornamental trees, shrubs and flowers are tolerant to preemergent herbicides. In fact, many are labeled for use in ornamental plants.

·         Post emergent herbicides will sometime cause yellow streaking in the lawn from damage, but preemergent herbicides don't.

Make sure that if you use a preemergent herbicide that the lawn has been established for at least a year. These herbicides can and often will severely injure freshly seeded or sprigged turfgrass. I speak from experience on this one.

Don't apply a preemergent herbicide in the spring if the lawn will be seeded, sprigged or sodded in the early summer, either. Preemergent herbicides persist in the soil anywhere from two to four months and will hinder establishment of new turfgrass.

Preemergent herbicides for lawns are sold under a number of trade names. Your County Extension Office and/or garden center store can help you select a preemergent herbicide.

Be sure to select one that's labeled for use on the turfgrass species in your lawn. The tolerance of turfgrass species varies among the different herbicides on the market.

Although preemergent herbicides won't control all the weeds in the lawn, they are particularly useful in preventing weed problems such as crabgrass, goosegrass and many other summer annual weeds.

  

Keith Mickler is the County Coordinator and agriculture agent for The University of Georgia/Floyd County Cooperative Extension. Located at 12 East 4^th Ave, Rome, GA 30161 (706) 295-6210. Office hours are Monday-Friday 8:00 a.m. - 5:00 p.m.

The University of Georgia Cooperative Extension - Learning for Life. Agriculture and Natural Resources, Family and Consumer Sciences, 4-H Youth.  An Equal Opportunity/Affirmative Action Institution. To obtain extension publications please visit our web site http://extension.uga.edu or contact your county Cooperative Extension office.