From the Vine: Fall Weed Program

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Labor Day has always been considered the last hurrah of Summer. Days are getting shorter, temperatures are getting cooler, and fall is just on the horizon. For gardeners and homeowners, Labor Day is also a signal to begin controlling winter annual weeds with a preemergent weed control program.

Winter annual broadleaf weeds germinate in the fall or winter and grow during any warm weather, which may occur in the winter, but otherwise remain somewhat dormant during the coldest days. They resume growth and produce seed in the spring and die as temperatures increase in late spring and early summer. They quickly invade thin turf areas, especially where there is good soil moisture. Many have a prostrate growth habit and are not affected by mowing.

If you had a weedy lawn last spring, it was mostly due to winter annual weeds that germinated and grew during the fall and winter. Winter turfgrass weeds common throughout the state consist of numerous annuals, biennials, and perennials. The main grassy winter weed is annual bluegrass or poa annua. Annual bluegrass is probably the most common and troublesome turfgrass weed in North Carolina. Winter broadleaf weeds are more diverse. There are many common cool-season perennials such as dandelion, white clover, mock strawberry, and mallow species. There are also many common winter annual broadleaf weeds such as henbit, chickweed, speedwell, knawel, lawn burrweed, Carolina geranium, and hop clover. Wild garlic is another cool-season perennial weed that actively grows in the fall.

To be effective, preemergent products must be applied before seeds begin to germinate, which is when soil temperatures reach approximately 70°F. A quick look at the average soil temperatures in Sampson County shows that the average soil temp is currently 77°F, so preemergents need to be applied sooner rather than later. Preemergents should also be watered in within 48 hours of application. You can either apply before a rain event or set your irrigation to run after applying the product. You will need approximately 1/2 an inch of water to obtain a uniformed barrier.

There are many preemergent products available. Look for products that contain the active ingredients benefin, pendimethalin, dithiopyr, or prodiamine. These products come as either a granular or liquid form. Both formulations are equally effective. Preemergents work by creating a weed barrier that kills weed seed once they begin to germinate. A second application should be applied after Thanksgiving to control any weeds that are late germinating. Make sure to read the label carefully before applying since manufactures often vary in their application requirements. You may also tank-mix preemergent herbicides with post-emergent herbicides such as metsulfuron, mesotrione, and 3-way herbicides if there are weeds present in the lawn.

By implementing a fall preemergent herbicide program, you can help your lawn get an early start in the spring without having the stress of competing with winter annual weeds.

The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina State University nor discrimination against similar products or services not mentioned.