Broadleaf and grass pests challenge lawns

Several lawn owners have recently contacted me about all of the weeds growing in their lawns. In many cases they treated their lawns with herbicides earlier in the season.

So, what is going on?

First let's consider broadleaf weeds such as dandelions, spurge, lespedeza and clover. When we have good growing temperatures, along with lots of moisture, these weeds tend to produce lots of seed or spread by runners -- which increases the weed population in your lawn.

The most effective method of control for most broadleaf weeds in your lawn is the application of the herbicide trimec. This herbicide, sold under many brand names, is a combination of three different herbicides which increases the spectrum of weed control while requiring less pesticide per acre to be used. Therefore you may need to spot treat your lawn with this product to keep the weeds under control.

One broadleaf weed, the violet, is not controlled by trimec. You need to use triclopyr for best control. Be careful with this herbicide. The labels give a range of different concentrations to use depending on what kind of vegetation you are going to control. On your lawn, always use the lowest concentration listed on the label when controlling violets.

Another concern has been the emergence in crabgrass and foxtail in lawns that were treated with a pre-emergent herbicide for control early in the spring. Under normal environmental conditions, depending on which pre-emergent herbicide is used, one or two applications in the early spring and late spring will give season long control.

Because of the excessive amount of rainfall this spring, the herbicides have been degrading more rapidly than normal. So we are now seeing the presence of these annual grasses.

At this point in time, foxtail and crabgrass can be controlled by an application of the herbicide quinclorac. This is often sold in combination with trimec. So an application of this herbicide combination can control many of the broadleaf and grass weeds found currently in your lawn.

One other weed has raised its ugly head -- nutsedge. You know you have nutsedge in your lawn when you mow it today and see a clump of "grass" needing to be mowed again tomorrow. This "grass" is actually a sedge. It grows rapidly during warm weather. You will find it in the wettest areas of your lawn.

The herbicide to use to control nutsedge is halosulfuron-methyl. You must also use a spreader-sticker when applying nutsedge control. More than one application may be needed. This particular weed is hard to control because of the nutlet found attached to the root system of the nutsedge clump.

All of these herbicides are sold by several trade names. If you are not familiar with these herbicides, go to a garden center that has personnel who can help you identify the problem weeds in your lawn, and can help you determine which herbicide to use to control them.