The saying, “Timing is everything,” could never be more true when it comes to weed control. Proper timing of herbicide applications can save you the frustration of dealing with a lawn full of weeds while also providing better control of those pesky plants. Properly identifying the weed and understanding its life cycle are important steps in selecting the best control method and getting the greatest results.
Know Your Weed
Knowing what type of plant you are dealing with is crucial to controlling it. Annual weeds require a different approach than perennial weeds.
Annual weeds sprout, grow, flower, produce seed, and die within one year. Annual weeds can be divided into three categories based on when they typically germinate. Spring annuals, such as crabgrass, germinate in the spring. Summer annuals, such as knotweed and sandbur, germinate later in the season. Winter annuals, such as henbit, germinate in late summer or fall, overwinter, and resume growth the following spring.
Each type of annual weed has different temperature and environmental requirements for germination.
Perennial weeds, on the other hand, continue to grow year after year. Plants such as clover and ground ivy can survive from year to year through their crowns, roots, stolons, or other plant structures.
Timing Herbicide Applications
There are several options for controlling weeds. Knowing the weed's life cycle and when it germinates can help determine the best time to apply a herbicide.
Preemergence herbicides are used primarily to prevent annual weed seeds from germinating, or sprouting. By stopping weeds before they emerge, these products can prevent them from becoming a problem in the first place. However, once a weed has germinated and begun growing, a preemergence herbicide is generally no longer effective at controlling that established plant.
Preemergence herbicides are also not effective for controlling established perennial weeds because these plants survive from year to year through their crowns, roots, stolons, or other structures rather than relying solely on new seedlings.
Postemergence herbicides are commonly used after weeds have germinated. Just like with preemergence herbicides, timing is important.
Early-season control of many weeds can provide better results. However, the best timing depends on the weed you are trying to control. For example, summer applications of broadleaf herbicides on perennial weeds may only injure or burn back the foliage temporarily. The plant may then produce new leaves and continue growing.
For many perennial broadleaf weeds, fall is an excellent time for control. As temperatures cool, perennial plants begin moving resources down into their roots and other storage structures in preparation for winter. Herbicide applications made at the appropriate time can move into these plant parts, resulting in better control.
On the other hand, applying herbicides to annual weeds late in their life cycle may provide little benefit. The herbicide may kill the plant only a few weeks before it would have naturally died from frost, while the plant may have already produced and dropped viable seeds. Knowing the weed you are targeting will help determine when herbicide control is most worthwhile.
Don't Forget the Elbow Grease
Herbicides aren't the only option for controlling weeds. Manually removing weeds may require a little elbow grease, but it can be an effective method of postemergence control.
Hand pulling or digging takes time, but removing weeds from the landscape also removes the developing or ripening seeds. When possible, remove the entire root system or as much of it as possible, and get the plant out of the landscape before it has an opportunity to produce or drop seeds.
Solarization for Large Areas
If you have a large area with an overwhelming weed problem and are considering completely rejuvenating the area, soil solarization may be an option.
With solarization, clear plastic is placed tightly over the soil surface for an extended period during the warmest part of the year. Heat from the sun builds beneath the plastic and can kill many weed seeds, seedlings, and some plant structures near the soil surface. For the greatest benefit, solarization is generally done over a large area for much of the growing season.
Be Patient
Patience is important when dealing with some weeds. You may think you have controlled a problem one year, only to see it reappear several years later.
Some troublesome weeds, such as Asiatic dayflower and puncturevine, can produce seeds that remain viable in the soil for several years. These seeds can sit in the soil until the right conditions occur for germination. Just when you think you have the problem under control, another flush of weeds may appear.
Stay vigilant and continue removing or controlling weeds before they have a chance to produce more seeds. Over time, you can gradually reduce the number of viable weed seeds in the soil and gain better control of the problem.
Proper identification, timing, and selecting the right control method are the keys to successful weed management. Take some time to identify the weed before reaching for the herbicide, and make sure the timing and treatment match the weed's life cycle. With a little planning—and maybe some elbow grease—your weeds might finally meet their match.