The Problem with Post-Emergent Herbicides
Post-emergent herbicides are instrumental in knocking out weeds once they have surfaced in the spring. Once summer weeds become established, they produce seeds to perpetuate the species, creating a vicious cycle of repeat spraying. Post-emergent herbicides work by killing growing plants, usually by interrupting chemical processes such as photosynthesis, protein production, or root growth. They are best applied when the plant is actively growing, which allows the herbicide to be drawn down into the roots where it is most effective.
Post-emergent herbicides can work on contact, killing only the vegetation they touch, or systemically, absorbing into and killing the entire plant. But there is a better way.
Meet Your New Best Friend: Pre-Emergent Herbicides
Have you spent countless hours pulling weeds by hand, or repeatedly spraying weed killers? Pre-emergent herbicides offer relief from that aggravating problem. They do not offer automatic salvation, but they are one of the most important weapons in a gardener’s arsenal.
Pre-emergent herbicides attack weed seeds as they begin to germinate by killing the immature root as it emerges from the seed. This means you interrupt the growing process before weeds even become visible. With pre-emergents, you are taking preventative measures for a weed-free yard.
Timing Is Critical
Application timing is critical for optimal results. Most pre-emergent herbicides have about a 90-day residual. By allowing gaps in the coverage, you may allow seeds to germinate and restart the cycle.
In the Mid-South, we have a unique situation. Although we live in the South where winters are supposed to be mild, we have had some very cold winters. In the North, where it can almost be certain it will remain cold all winter, a winter application of pre-emergent is not necessary. Here in the Mid-South, where the weather can swing from cold and rainy to sunny and warm, a winter application can help eliminate the weeds that appear when the sun comes out and temperatures rise. Generally, a pre-emergent is applied in late summer to early fall, usually mid-September to early October, but Mother Nature does not always follow the calendar. Give us a call if you have any questions about timing.
A Three-Application Program
Your first application controls early-germinating Poa annua and other winter weeds. Your next application, put down 80 to 90 days after the initial application, helps stop other cool-season weeds and more Poa annua. Your third application, 80 to 90 days after your winter application, is probably the most important. It helps stop broadleaf weeds and, most importantly, crabgrass.
Why Crabgrass Is So Difficult
Crabgrass is a very invasive grassy weed that is difficult to eliminate using weed killers. Post-emergent non-selective weed killers will kill crabgrass but will also kill the surrounding lawn. Selective weed killers help eliminate existing crabgrass but do nothing to stop future generations from growing right back where you just sprayed.
Crabgrass produces a toxic chemical that inhibits the growth of plants around it. Once entrenched, it will soon start affecting your entire lawn. One single clump of crabgrass can produce over 100,000 seeds during a typical growing season. These seeds are spread every time we cut the lawn. Bagging helps, but it is not the answer.
The Right Product
Hi-Yield Turf and Ornamental Weed and Grass Stopper containing Dimension provides superior control of crabgrass, as well as control or suppression of other listed weeds, when applied before they germinate. It will also provide post-emergent control of crabgrass up to 4 weeks after germination. This product can be applied to both warm and cool season grasses and, unlike most other brands, can be used in flower beds and other landscape areas, as long as you do not plan to plant seeds in those beds.
If you plant a fescue grass yard or plan to overseed your Bermuda or Zoysia lawn, take great care with pre-emergent prior to seed planting. Pre-emergent can have up to a 120-day residual and will impede the germination of grass seed. It is also best to wait to use pre-emergent on new lawns. Allow your grass to become well established with adequate root growth before treating with any chemicals.
Give Your Lawn a Rest in Summer
Too much of a good thing is not good for you. By constantly bombarding your lawn with the same chemicals, root damage can occur. We recommend giving your yard a rest during the peak growing season and either pulling weeds by hand or using a post-emergent weed killer for the few weeds you may see throughout the summer. Use the summer months to enhance the soil and treat your lawn with products that will make both the grass and soil healthier.
The Bigger Picture
Conquering a weedy lawn is quite a challenge, but you can be successful if you keep one thing in mind: weeds are a signal that the grass in your yard is not happy. A healthy, thick lawn will naturally be low in weeds. Use pre-emergent to stop weeds before they start. Use organic lawn foods to feed not only the plant but the soil as well. Water deeply to allow for healthier root growth, and give your yard a summer treat by spraying with liquid seaweed or fish emulsion. It may take a little time to get your yard back, but once you do, you will be the envy of the neighborhood.