October 6, 2016
Fall Lawn Weed Control
We are just entering the best time of year to control many problem broadleaf weeds in turf. October is a GREAT time to control dandelions, white clover, ground ivy and other perennial weeds that are a perennial problem for people trying to keep their lawns looking nice. Actually you might want to wait a week or two until we’ve had a killing frost. Most of these weeds will tolerate a light frost, but it will bring an end to many of our ornamentals, lessening the chance of accidental drift and injury to non-target plants.
There are several reasons fall is the best time to control these weeds. In fall, these plants are making food for next year’s growth and sending it to the roots where it will be stored until used by the plants next spring. Herbicides applied at this time of year will also be transported to the roots, providing superior control if the plant has adequate moisture and warm temperatures.
The way it has been raining this fall, moisture doesn’t seem to be a problem. If things turn dry by the time you are going to treat your lawn weeds, water the lawn before applying a herbicide so the plants have adequate moisture, but you won’t wash the product off which would happen if you water after treatment. You can help insure plants will metabolize and transport the herbicide by selecting a day to treat when temperatures will get to 60OF or above.
A second advantage of fall treatments is, depending on the growing conditions in the fall, you can often go back two or three weeks after your initial application and spot treat individual weeds that weren’t controlled with the first treatment. Remember to consider the moisture and temperature when making these spot treatments. Later in the fall, good days may be harder to come by.
Finally, even if you don’t completely control the weeds this fall, you may weaken them and they are more likely to winterkill. You probably won’t get 100% control this fall, but you can greatly reduce the weeds in your lawn. Even though it isn’t an ideal time to control them, treat weeds that escape your fall treatments next spring to help prevent them from becoming reestablished.
Often homeowners will ask why they didn’t get good weed control when they treat their lawns in spring or summer. In spring, the major movement of moisture and nutrients in the plant is from the roots to put on new top growth. While growing conditions are generally good in the spring, less of the herbicide is translocated to the roots. Often what will happen is the homeowner will kill or burn back the top growth, only to have the weeds come back from the roots later in the growing season.
In summer, conditions are usually too hot and/or dry for these weedy plants to be actively growing. When the weeds aren’t growing, there is reduced metabolism and movement of the herbicide in the plant resulting in poorer control. Summer is probably the least effective time during the growing season to try to control these weeds.
Here are a couple other reminders for lawn care this fall...
· Leave your mower on the highest setting or about 3-3½ inches tall. It is not necessary or recommended to lower the mowing height in the fall. Taller grass will catch more snow which provides a protective layer over the turf, lessening the chances of winterkill if we have a winter with little snow. Turf is much more likely to be damaged when exposed to the winter weather.
· Be sure to mow and mulch or rake leaves as they accumulate on your lawn. Mowing and mulching leaves returns nutrients to the soil, but if there are so many that piles of ground up leaves and clippings are left behind your mower, mow over the area again to filter them into the turf or bag and remove them. (The compost pile is a good destination for bagged leaves and grass clippings.) Piles of clippings or ground leaves on top of the turf can smother the turf below. Don’t allow a layer of leaves to accumulate on the turf. When moisture mats these down, large areas of turf can be damaged or killed resulting in the need to overseed or reseed next spring.
· Finally, it seems illogical, but applying about half to three quarters of a pound of actual nitrogen per 1,000 square feet of turf around Halloween can be the most important fertilizer application you make all year. Even though the top growth has usually stopped by then, the roots are still active. Applying fertilizer then will strengthen the roots and give you a nice, even, slow green-up next spring. Then you shouldn’t need to fertilize your lawn next sprint until you apply your preemergence product around May 1.
For more information on weed control and fall lawn care, contact your local Nebraska Extension office.