During this transition time of fall, summer annual weeds are approaching the end of their lives. At the same time, winter annual weeds are getting ready to begin a new life. Understanding this concept is critical when it comes to controlling annual weeds.
Summer annual weeds like crabgrass, spurge and knotweed have completed about 80% of their lifetime as we move into October. By now they’re the dominant weeds in many yards. They’ve reached maturity and produced hundreds if not thousands of seeds. The first killing frost will kill these summer annual weeds. Most people wait too late to ask about controlling these weeds.
The best time to control weeds is while they’re young and before they’ve had the opportunity to reproduce. This includes cool season annual weeds that are about to germinate.
Even though you may have missed the best time to control the summer annual weeds for this year, you’re right on time to make plans for controlling winter annual weeds.
Timing of the herbicide application is of utmost importance in controlling winter weeds that are about to sprout in home lawns. Common winter weeds include annual bluegrass, chickweed, henbit, hop clover, lawn burweed and Carolina geranium.
These and other winter annual weeds germinate from seeds during fall as soil temperature cools and day length shortens. The little seedlings usually go unnoticed at this time, but continue to slowly grow through the colder winter months. Approaching spring, as day length becomes longer and soil temperature warms, these previously inconspicuous weeds put on a growth spurt.
The majority of calls for advice on winter annual weed control come to me in late February through April when these weeds are most visible. By then, it’s too late. The parent plants are dying and seeds have been scattered all over the yard. You should now see why timing is important when controlling these weeds.
If you intend to use a preemergence herbicide, apply it during October when nighttime temperatures drop to 55° to 60°F for several consecutive nights. This will be just before the weeds emerge.
Some preemergence herbicides to look for include oryzalin (Surflan), benefin (Sta-green Crabgrass Preventer, Hi-Yield Crabgrass Preventer) and pendimethalin (Pre-M, Pendulum, Turf Weedgrass Control, Scott’s Halts). There are others – check with local garden supply stores.
Not every lawn needs an application of preemergence herbicide. If your lawn has had no problem with winter annual weeds, there’s probably no need to apply a preemergence herbicide to prevent non-existent seedlings from emerging.
It is the user’s responsibility to read and follow all label directions and precautions when using any pesticide, including herbicides.