Weed Control in Spring Lawns

Based on the number of lawnmowers that I have seen out within the last week, I think it is safe to say that Spring is finally here.  I know many of us were excited to gas up the mower and shake off the dust for the first time this season.  Now that mowing season has finally kicked off, it is time to start thinking more about spring lawn care.  Having a well-manicured lawn will improve the aesthetics and value of your property, and it really isn’t as hard as it sounds.

Weed control plays a huge part in having a healthy lawn.  The best defense against weeds in home lawns is a healthy, dense lawn.  In thick lawns, weed seeds may not germinate because light may never reach the soil surface. A thick lawn is com­petitive with weeds, keeping them from growing and reproducing. Developing a healthy and dense lawn comes from using cultural practices such as proper grass species and cultivar selection, proper mowing heights and fertilization, and other good management practices. The need for herbicides to control weeds in home lawns can be greatly reduced if the lawn is well maintained.

There are instances, however, when weeds escape and more aggressive con­trol tactics are necessary. Even in well-maintained lawns, weeds can become a problem. Some weeds adapt to lawn management practices, and diseased or drought-stressed lawns can result in thin turf and create openings for weed germination. Control tactics can in­clude herbicide applications or physical removal of the weeds. In small areas, or if the weed infestation is not severe, physical removal is the control method of choice. However, an herbicide application can provide the lawn a better chance of successfully competing with weeds.  For all weeds, herbicide treatment when the weeds are young will result in the easiest and best opportunity for control using the least amount of herbicide.

Herbicides available for use in home lawn weed control can be classified by when they are applied—either before or after weeds appear—and whether they are selective or nonselective. A pre-emergent herbicide is applied before weeds appear and controls them as the seed germinate. A common misconcep­tion is that pre-emergent herbicides kill weeds before they germinate. Actually, pre-emergent herbicides form a residual barrier in the upper soil layer and must be applied prior to weed seed germination to be effective. When seeds germinate and young weed seedlings begin to grow near the soil surface, the seedling comes in contact with the herbicide barrier. The herbicide is then taken into the plant, and the weed dies. Lawn grasses with established root systems are unaffected by the herbicide barrier.

Selective post-emergent herbicides are applied after weeds germinate and plants are visible.  The most commonly used post-emergent, selective herbicide is 2,4-D.  These herbicides are most ef­fective when applied to young, actively growing weeds. Most pre-emergent and post-emergent herbicides selectively control the undesired species without damaging the turf. Nonselective her­bicides, usually applied post-emergent, often will injure or kill all plants within the treated area, both desirable and un­desirable ones that come in contact with the herbicide. Nonselective herbicides are typically reserved for spot treatments or total renovation of an area.

Spot treating weeds is typically per­formed with a handheld sprayer. This method of weed control can be very ef­fective and uses less herbicide. However, because non-selective herbicides will kill your desired lawn species as well as the weeds, the application must be carefully controlled to keep these spots as small as possible.

Some herbicides are packaged with a fertilizer as a “weed and feed” product. These products should be avoided in the spring for cool-season lawns, which are composed of tall fescue, Kentucky bluegrass, and perennial ryegrass. In Kentucky it is recommended that fertil­izer should not be applied to these lawns in the spring. Spring and summer fertil­izer applications lead to increased lawn disease and weed infestations. The best time of year to fertilize cool-season lawns is in the fall, not with “weed and feed” in the spring and summer.

Remember that the best defense against weeds is a healthy lawn. Using good management practices may make herbicides unnecessary, but if you expe­rience weed problems, you may choose to apply an herbicide to give your lawn a fighting chance to successfully compete with the weeds. You must identify the kind of weed you want to control so that you can choose the herbicide that will be effective in your environment. Read the herbicide labels and if you have any questions, please contact the McLean County Cooperative Extension Office at (270)273-3690.

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