Controlling fall weeds in northwest Kansas lawns
Late October to early November is the most effective time to control broadleaf weeds in lawns. Dandelions usually produce a flush of new plants in late September, and the winter annual weeds henbit and chickweed should have germinated in October. These young plants are small and easily controlled with herbicides such as 2,4-D or combination products (Trimec, Weed-B-Gon, Weed-Out) that contain 2,4-D, MCPP and Dicamba.
Even established dandelions are more easily controlled now than in the spring because they are actively moving materials from the top portion of the plant to the roots.
Herbicides will translocate to the roots and will kill the plant from the roots up. Choose a day that is 50 degrees or warmer. The better the weed is growing, the more weed killer will be moved from the leaves to the roots. Cold temperatures will slow or stop this process.
Weed Free Zone (also sold under the name of Speed Zone) contains the three active ingredients mentioned above, plus carfentrazone. It will give a quicker response than the other products mentioned, especially as temperatures approach 50 degrees.
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Sometimes you will hear people say to let the grass grow tall right before the onset of winter. Their reasoning is the extra foliage will insulate the crown of the plant from the extreme cold of winter. Although this might sound reasonable, in practice it probably does little, if anything, to increase winter hardiness. On the contrary, a canopy that is too high during the winter might lay over and become matted down, leading to an increased incidence of winter-diseases such as snow mold.
Turfgrass species vary genetically in their cold tolerance, with warm-season grasses being less cold tolerant than the cool-season types. Given these differences, cold tolerance is improved by increasing the health of the plants going into the winter, and healthy plants are a result of a sound management program (fertilizing, watering and mowing) during the spring, summer and fall. The lawn will benefit more from continuing to mow at the recommended height than from trying to gain some insulation against winter cold by allowing it to grow tall.
Here is a list of the recommended mowing height ranges (in inches) for home lawns in Kansas: tall fescue, 2.5 to 3.5; Kentucky bluegrass, 2 to 3; perennial ryegrass, 2 to 3; buffalograss, 2 to 3; Bermudagrass, 1 to 2; and Zoysiagrass, 1 to 2.
There might be some benefits gained by adjusting mowing heights within the recommended range at times. For example, it is a good practice to mow warm-season grasses at the higher end of recommended heights during late summer and early fall, which should help them store more carbohydrate reserves for the winter. It also could reduce the incidence of certain cool-weather diseases. But the rule to remember is to stay within the recommended height range for your species.
Stacy Campbell is Ellis County agricultural agent with Kansas State Research and Extension.