For all who have been anxiously waiting, now is the time to control broadleaf weeds in your lawns.
Whether they’re actively growing to prepare for winter or newly germinated, these weeds are vulnerable now. Control will be more effective than when the weeds are more established or during times of slow growth, when they’re less receptive to chemical applications.
Dandelions, henbit, chickweed and knotweed can all be controlled effectively in the fall. During late October and early November, dandelions, a broadleaf perennial, are producing a new flush of growth. Henbit and chickweed, which are broadleaf annual weeds, are newly germinated and easy to kill.
Even established dandelions are easier to control because they are actively moving resources from the top portion of the plant into the roots. That means the plants will absorb herbicides as they would nutrients, killing them from the bottom up. Anyone who has tried to pull dandelions by hand knows that leaving any part of the root in the ground will result in a new plant sprouting. By using properly timed chemical control, every part of the plant is killed, preventing resprouting.
These broadleaf weeds can be controlled with combination products such as Trimec, Weed-B-Gon, or Weed-Out that contain 2,4-D, MCPP and Dicamba. For optimal results, spray on a day that is 50 degrees or higher. A warmer day encourages weeds to grow more, moving more chemicals to the roots. Cooler days can be effective but may slow the process and, in some cases, may render the chemicals ineffective. Weed Free Zone (also sold under the name Speed Zone) contains the three active ingredients mentioned above, plus carfentrazone. It will give a quicker response than other products, especially as temperatures approach 50 degrees.
Knotweed, another annual broadleaf, thrives in compacted soils. Aerating your soil creates an unfavorable environment for knotweed and is the best first step in control. Maintaining a healthy lawn will help eradicate this and other weeds.
Unlike the newly germinated henbit and chickweed, knotweed germinates in late February or early March, so fall is the time to apply a pre-emergent herbicide. Pendimethalin (Scotts Halts), Surflan (Weed Impede, Barricade, Dimension and XL) are all labeled for knotweed. Pendimethalin, Barricade and Dimension can be used on all Kansas turf grasses, while Surflan and XL can only be used on tall fescue and warm-season grasses.
In the spring, a post-emergence product, such as Trimec, Weed-Out, Weed-B-Gon or Weed Free Zone, can be applied after knotweed has germinated but when it is still young. A spring-seeded lawn will affect chemical selection. Trimec requires a month before overseeding in order to allow for lawn establishment. Never use a pre-emergent herbicide when seeding or reseeding a lawn.
For anyone who would like still like to seed their lawn, that time has passed. Kentucky bluegrass and tall fescue should be seeded in September but no later than Oct. 15. Though plantings later than Oct. 15 can be successful, the odds of success diminish as time passes. The problem with late plantings isn’t that the seed won’t come up or that young grass plants are sensitive to cold — most often, the problem is with rooting. Unless the young grass plants have a fairly extensive root system, winter freezing and thawing heaves plants out of the ground, and they dry out and die.
Regardless of when your lawn was planted, be sure the new lawn is kept watered through the fall. More mature lawns will need less frequent watering, but all should go into the winter with moist soil.
As with all chemical use, reading and following the label exactly is critical for effective results. Weed identification is also key to successful control.