A weed is a plant out of place. Seems like such a ‘nice’ definition for these little plants. Weeds can be issues in many areas, but it always seems that they are the most plentiful in the lawn. The key to knowing when to pull and when to spray depends on the weed and time of year. It all comes down to proper identification of the weed and its life cycle.
Winter annual weeds bloom in the spring, produce seed, and die all before the temperatures get hot. One of the more common winter annual weeds is henbit, which is the ‘pretty’ purple flower in bloom in the road ditches. Henbit has scalloped leaves, a square stem, and little purple flowers at the tip of the stem. These weed seeds germinated last year in September or October. The little plants sat dormant throughout the winter just waiting for the right time to jump into flower and seed production. Right now, a post emergent herbicide, products like 2,4-D, can be applied, but they might not do that much good. Spraying might make you feel better, but it can cause the plant to produce and drop its already mature seeds. If the area isn’t too large, you can hand-pull these weeds. Also, look at the density of your lawn in the areas where the weeds are located. Is it thin? You might need to figure out why the turfgrass isn’t competing with the winter annuals and a cultural practice change might be needed to promote grass growth and density in that area. If herbicide control is needed, preemergence herbicides should be applied in early September to control winter annual weeds.
Summer annual weeds germinate in the spring, grow throughout the summer months, and produce seeds and die before winter. One of the most common summer annual weeds is crabgrass. Crabgrass is an annual grass that often fills into areas where the turfgrass is thin. There are products that you can apply now to help keep the crabgrass problem at bay. Crabgrass preventers, or preemergence herbicides, will help you in this fight against crabgrass. These products will only work to keep seeds from germinating, or beginning to grow, not for plants that are already growing. Crabgrass needs a minimum soil temperature of 50 to 55 degrees to begin germination. Preemergence herbicide applied just prior to germination provide the longest period of control. In most years, the optimum time to apply preemergence herbicides for crabgrass are between the end of April to early May. A second application might be needed in mid to late June to give complete weed control. Remember that these products need to be watered into the soil profile for best control.
Perennial weeds come back year after year. The common offenders include white clover and ground ivy. Ground Ivy looks very similar to henbit, but the control methods are very different. Ground ivy also has scalloped leaves, a square stem, and purplish flowers, but the flowers are in the leaf axil, between the leaf and the stem. Positive identification is key to the control method. Since ground ivy is a perennial and comes back year after year, a post emergence herbicide will be needed. If the product is applied now, the foliage might be burned back, but the plant will regrow. The best time to apply post emergence herbicides for perennial lawn weeds is in October with a combination herbicide, like Trimec that contains 2,4-D, MCPP, and dicamba. These products will also work well to control other weeds like clover or dandelions in the lawn.
With proper identification and timing, these out-of-place plants can be controlled.
For more information contact Elizabeth Killinger at firstname.lastname@example.org, 308-385-5088, on Facebook, Twitter, her blog at https://huskerhort.wordpress.com/, or visit the University of Nebraska-Lincoln Extension website: hall.unl.edu.