Warm weather and timely rains means two things. Spring is here. Weeds aren’t far behind. Find out what you can do now to help prevent weeds from taking over your lawn this year.
Crabgrass is the main target for early season preemergence herbicides in turf. It needs a minimum soil temperature of 50 to 55 degrees to germinate. Normally, that soil temperature is reached the end of April or the beginning of May. This year, however, we might reach those optimum germinating temperatures a bit sooner than expected. The soil temperatures for Grand Island were close to 47 degrees at the end of March. To see what the soil temperatures are in your area, you can visit http://cropwatch.unl.edu/cropwatchsoiltemperature.
Don’t get into too big of a hurry to apply the preemergence herbicides. If crabgrass does happen to germinate before April 15th, there is a chance that the little seedlings could get hit by frost. Our average frost free date in Central Nebraska is around Mother’s Day, so there is a good chance for at least one more frost yet this spring. Don’t let air temperatures fool you, it’s the soil temperatures that matter. The soil will warm up slower than the air temperatures. Just because we might have several nice days in a row, doesn’t mean the soil temperatures are increasing rapidly. Always check the average soil temperatures at the 4” depth to be sure.
Preemergence herbicides are designed to prevent seeds from sprouting. The three most common active ingredients in preemergence herbicides are dithiopyr, pendimethalin, or prodiamine. When choosing a product to control crabgrass, look for one of those active ingredients. Once a plant is up and actively growing, not all preemergence herbicides will work. Products containing prodiamine or pendimethalin may control one-leaf crabgrass if watered in immediately following the application, but should be applied before germination for optimum control. Dithiopyr will control crabgrass before tillering, sprouting off-shoots, and can be applied later than the previous products. Be sure to water in the products after application to keep it from degrading in the sun.
If you did happen to put down the preemergence herbicide don’t worry. Just think about a spit application. For extended season control, consider a split application of the preemergence herbicide. A split application of preemergence herbicides will allow for a longer control window. Aim to put down half the highest recommended application rate on the label now and the other half in 6-8 weeks for season long control of weeds. One application now probably won’t last throughout the entire growing season because of the earlier application window.
Increasing the density and health of the lawn in the thin areas can help in the fight against weeds. Improve the lawn either by overseeding or by changing cultural practices to promote grass growth. Preemergence herbicides will also prevent turfgrass seeds from germinating. You can opt to not apply preemergence herbicides in the areas where you will be overseeding or you can be selective which products you apply. If you are considering overseeding this spring and still want to apply a preemergent herbicide, be sure to read the label on the preemergent to know if/when you can overseed following the application or if you can apply the preemergent over the top of grass seedlings. If you can’t overseed the lawn this spring, there is still time in the fall to successfully overseed. One advantage to fall seeding over spring is the decreased weed pressure.
Take advantage of the warm weather, check your soil temperatures, and prepare to do battle against crabgrass.
Elizabeth Killinger is the Horticulture Extension Educator with Nebraska Extension in Hall County. For more information contact Elizabeth at firstname.lastname@example.org, her blog at https://huskerhort.com/, or HuskerHort on Facebook and Twitter.