(By Jared Hoyle, KSU Turfgrass Research and Extension)
One of the most common weed control recommendations for winter annual weeds is “keep it mowed and let them die because of the warmer weather”. Well right now it is March 30th and it is prime winter annual weed growing weather. Yeah, it might warm up in the next week but what if this is what we recommended in February when we have a week of 75 deg F weather. We would have been waiting about 2 months before mother nature would have taken care of that weed problem. So here is some information about winter annual weeds and control.
The plant with the little tube shaped purple flowers that have been showing up turfgrass is called henbit. If you are not sure this is what you have, check the stems. If they are square rather than round, you have henbit. Square stems are an indication that it is in the mint family. Henbit is a winter annual broadleaf with kidney shaped leaves, opposite arranged, with rounded teeth on the leaf margin. The upper leave surround the stem. It really likes disturbed, moist areas in turf and landscape beds. Don’t get it mixed up with purple dead nettle or ground ivy, they are similar looking weeds. Most broadleaf weed herbicides are effective.
A plant that also is low growing but has round stems and tiny white flowers is chickweed. Chickweed is also a winter annual and starts to grow in the fall. They spend the winter as small plants and so most people do not pay much attention to them until they start to flower in the spring.
Remember, these are winter annuals that will die as soon as the weather turns hot. You can keep the turf mowed and you can let nature take its course. As you can see this year it got warm, then cold, then snowed, then warm again, dry and now 50’s – low 60’s and raining. So waiting may not be an option for golf courses, parks, sports complexes, and lawns. We may need a jump start to get rid of those weeds.
Ok so here is a scenario. We wait and let the warm weather kill off the winter annual weeds. Now there is a void in the turf. What happens in voids in our turf as it warms up? Crabgrass starts to germinate. Hope you got your preemerge herbicide out for crabgrass!
Fall is obviously the best time to kill broadleaf weeds but these weeds will germinate throughout the Fall to Spring. The majority germination in October but they will continue to germinate through the spring especially when we have those warm fall and winter days. So a Fall application in November may not get complete control because more will germinate after that application. Thats why a Spring application may be needed as well to clean up these weeds along with some dandelions that may have also survived. Most broadleaf weed herbicides are effective especially ones that are three-four way mix. FYI, at this time the weeds are more mature and harder to control.
Always remember to READ THE LABEL for the correct rate, turfgrass tolerance, and specific instructions before application!!!
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