Bill Starr: Spray now to avoid a sticky situation

Published 12:45 pm Monday, February 6, 2017

I am sure that many of you remember the endless complaints from small children and even pets last spring as temperatures warmed and they wanted to go play in the yard. Thousands of tiny burs made it impossible to enjoy the nice spring weather. The culprit is what we refer to as spur weed or lawn bur weed. If it were not for the spine tipped burs that form as the plant matures it would probably go unnoticed.
This is one of those winter annual weeds that a fall or early winter application of Atrazine would have controlled. Lawn bur weed can be easily controlled during the winter months. December, January and February are ideal months to apply herbicides for the control of this weed. It seems,  however, with another mild winter and grass that was thin due to summer drought stress, it is a weed we need to deal with in 2017 again.
The weed germinates in the early fall months as temperatures cool and remains small or inconspicuous during the cold winter months. However, as temperatures warm in the early spring, or about the same time as spring sports activities, lawn bur weed initiates a period of rapid growth and begins to form spine-tipped burs in the leaf axils. The sharp-tipped spiny burs of this weed can cause minor irritation to the skin.
It is not that we can’t control this weed in March, April or May, but by then the burs will have already formed. If we control this weed now we can reduce the pains of spring. There are several herbicides that work well and are safe on our grasses at this time of year. Any of the three-way mixes (usually containing 2, 4-D, MCPP, and Dicamba) can be used and do a good job. As centipede and St. Augustine begin to green up you need to avoid these or use reduced rates. This group of products should be applied on a warm, sunny day with air temperatures at least 55 degrees F. Two to three weeks after the initial application, lawn bur weed control should be evaluated. If control is not acceptable, an additional application may be necessary.
Other herbicides like those containing metsulfuron can be safely used on all of our turf grass species. Products containing this herbicide are used at very low rates so you need to be sure and read the label. High rates of metsulfuron can injure or kill our grasses, and it should definitely not be used if Bahia grass makes up the majority of your lawn. (It will kill Bahia grass).
The key factor to effectively controlling lawn bur weed is to apply an appropriate herbicide during the winter months. Lawn bur weed is small and easier to control at this time of the year than in April and May. Also, turf grasses are not actively growing during the winter months and have better tolerance to some herbicides. Lawn bur weed can be controlled in late March, April and early May. However, two main facts should be considered. Lawn bur weed begins to die as late spring temperatures approach 90 degrees F. and the plant is harder to control once the spiny burs or stickers have formed. Multiple herbicide applications are usually necessary, which increases the risk of temporary injury to the turf grass. Additionally, it takes time for the herbicide to control lawn bur weed, and after death, it takes time for the dead lawn bur weed plants to decompose. Therein lies one of the main problems with late treatments. Dead lawn bur weed plants contain dead, or brown spine-tipped burs. Dead or alive, the spiny burs still present a problem. The only recourse at this point is to allow time for the plant to naturally decompose.
I am going to say that if you had it last year you will probably have it this year as well, and it is growing well with recent rains and warm weather. As always when using pesticides read and follow all the label instructions.

Bill Starr is Sumter County Extension agent/coordinator, University of Georgia Cooperative Extension Service. Contact him at 229-924-4476.