Kill weeds in early fall to ensure a lush lawn

Q&A With Sandy Feather

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Editor's note: This is Part 1 of Sandy Feather's annual column on maintaining a healthy lawn.

Q. As a new homeowner, I have lots of questions about lawn care. Most of my neighbors use a lawn service. I prefer not to use a lot of pesticides but would still like my lawn to look nice. It does have a lot of weeds, and I am willing to use some herbicides to get them under control. Are there cultural practices that would help keep it nice without constant spraying?

A. Proper cultural management of your lawn will go a long way toward improving its health and appearance without using a lot of pesticides. You may need to make a few herbicide applications at first to get the weeds under control. After that, you can control the occasional weed by hand pulling or spot treating with a liquid herbicide. Your best defense against weeds is a lush, thick lawn.

Late summer and early fall are excellent times to control many lawn weeds, especially tough perennial weeds such as clover. At that time of year, perennial plants are translocating the products of photosynthesis to their roots for storage over the winter and absorb herbicides readily. Tough customers such as clover and ground ivy will require repeated applications.

While granular weed and feed products are useful, they have their limitations. They must be applied to a lawn that is moist from dew or rain so that the granules stick to the leaves of the weeds in order for them to absorb the herbicide. And you cannot make a second application of weed and feed to go after those tough weeds -- that would be too much fertilizer in too short a time.

Liquid broadleaf weed killers allow more flexibility. If you have weed and feed on hand and have not fertilized your lawn in six to eight weeks, you can make the first application with it, then make subsequent applications with a liquid.

Broadleaf weed killers typically include active ingredients such as 2,4-D, MCPP, MCPA, dicamba, carfentrazone and triclopyr. Active ingredients are listed in fine print, usually on the lower left corner of the pesticide label. They are generally sold as combination products to take advantage of the synergistic effect of these herbicides together. (If you have a lot of trees in your yard, do not use products containing dicamba within their root zone, or choose a product that does not contain dicamba.)

They are available as ready-to-use hose end applicators or as concentrates that you mix and apply with a pump sprayer. The pump sprayer offers more control; hose end sprayers are convenient and you do not have to measure and mix spray solutions. Whichever you choose, always read and follow mixing and spraying directions carefully. The label contains important information on using the product for maximum safety and effectiveness.

If you choose a pump sprayer, reserve it strictly for spraying herbicides; never use it to apply insecticides or fungicides to plants that you value. Even if you clean it out, there may be enough herbicide residue to damage them.

You may need two or three applications to get sufficient control of tough-to-kill weeds. Check the label of the herbicide you are using for suggested application intervals. Even though some of these weeds seem indestructible, re-spray at the shortest recommended intervals until you are satisfied.

Mowing practices greatly determine the quality of lawns. Allowing a lawn to grow long and then cutting it short is stressful to grass. It uses a tremendous amount of its stored energy reserves to push out new growth after such treatment. The general rule of thumb is not to remove more than one-third of the leaf blade at one time.

Rather than mowing on a schedule -- say, every Saturday -- mow as the grass's growth dictates. That may be twice a week during the cooler weather in spring and fall or every few weeks during hot, dry summer weather (especially if you do not water).

Most species of turfgrass should be cut at a height of 21/2-3 inches. There is a direct relationship between the height of cut and the depth and extent of the root system. The longer the grass grows, the more extensive its root system; the shorter you cut it, the less root system it will have. Summer heat and drought are more stressful for our cool-season grass species than winter cold. Keeping the grass a little taller encourages an extensive root system that will make your lawn more drought-tolerant. It also shades the soil, moderating soil temperatures and helping to conserve soil moisture, as well as shading out germinating weed seeds that try to become established.

Be sure to sharpen your mower blade regularly. A sharp blade makes a clean cut that the grass recovers from easily. Dull blades make jagged wounds that are harder to heal. They can serve as a point of entry for insect and disease problems.

How often you sharpen your mower blade depends on the size of your lawn and the number of obstacles it is likely to encounter. Monthly sharpening for large (or obstacle-filled) lawns is not unreasonable. Small lawns can get by with once a year.

Next week: Proper watering and dethatching. Send questions to Sandy Feather by e-mail at or by regular mail c/o Penn State Cooperative Extension, 400 N. Lexington Ave., Pittsburgh 15208.


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