- Ada, Oklahoma

October 16, 2006

Control of Sandbur in Oklahoma Lawns

Justin McDaniel

Control of sandbur in Oklahoma lawns is possible using a well planned and executed management program. Sandbur is a warm-season grass commonly found on dry, low fertility sandy sites throughout Oklahoma. The weed derives its name from the spiny fruit that it produces, which contain the true seeds of this very drought resistant plant.

 A survey of sandbur species conducted earlier this decade from turfgrass areas in Oklahoma found that 98% of the types were of the species field sandbur and only 2% were of the long-spine sandbur species. Field sandbur often behaves as a short-lived perennial plant in Oklahoma, while the long-spine species usually behaves as a true summer annual. It is usually not feasible for the untrained observer to determine which species is present in their lawn. Contrary to the common name of each plant, it is not spine length but rather spine number that is used to determine which species is present. Now, who really would enjoy getting their microscope out and counting the number of spines on sandbur fruits?

 Sandbur management involves practicing an integrated pest management (IPM) approach. This involves using a well adapted warm-season and drought tolerant turfgrass such as bermudagrass in full-sun areas, followed by proper mowing, fertilizing and irrigating of the turf. Lastly, control of existing sandbur plants is achieved by supplementing the program with post-emergent herbicides and guarding against new sandbur plants using pre-emergent herbicides.

 Common or hybrid bermudagrass is often the best adapted turfgrass for lawns on sandy soils where sandbur plants are most often found. The desirable grass needs to be managed to provide 100% ground cover.

 About 3 to 5 lbs total of actual nitrogen is applied per 1,000 sq. ft. of lawn area per year in a sandbur management program. This total amount of nitrogen fertilizer is split into about 3 to 5 total applications during a growing season. On sandy sites, the use of slow or controlled release fertilizer is highly suggested. This is because sandy soil is a poor nutrient holding soil and if too much fertilizer is applied at one time, it will simply wash through the soil, out of the range of turfgrass roots and potentially pollute ground water.

The fertilizer applications are made from late April through mid-September, on a monthly to a month and a half basis. Optimum levels of soil available phosphorus and potassium help bermudagrass remain competitive on these low nutrient sites. The only way to know what soil P and K levels are is to obtain a soil test on your lawn. Select a minimum of 10 soil subsamples from the top 4 to 6 inches of your lawn and pool these for a total sample size of about ? pint. The sample can be brought to the Extension office where the sample is shipped for testing. The basic soil test costs only $10 and it tells you the soil reaction (pH value) as well as the nitrogen, phosphorus (P) and potassium (K) availability indices. The amounts of P and K to add to the lawn are based on this soil test. On sandy sites, because of their low nutrient holding capacity, often very small amounts of P and K are applied eac

h time that nitrogen fertilizer is applied, according to soil test recommendations, in an effort to spoon-feed the grass to optimize its performance and also in concert with sound environmental stewardship.

 Mowing is practiced at the optimum height and frequency for the specific turf being grown. For bermudagrasses, this will be between 1 and 3 inches, depending upon the variety and management intensity that is planned. The lawn is mowed often enough that not more than 1/3 of the top growth is removed in a single mowing so as not to too severely shock the grass. For example, if the mower is set at 1.5 inches the lawn needs to be mowed when it reaches 2.25 inches. If the mower is set at 2.0 inches, the lawn needs to be mowed when it reaches 3.0 inches.

 All plants need water to grow. Although bermudagrass is one of the most water use efficient and drought tolerant of the adapted turfgrass for Oklahoma lawns, it too needs water during dry periods. For best results, bermudagrass will be most competitive against sandbur when the bermudagrass is not allowed to go dormant during a drought. About 1.0 to 1.5 inches of water per week will be needed to keep bermudagrass lawns going during a drought in summer. Sometimes availability of water is not present or its high cost or short supply simply means that the homeowner will not be able to water much in summer. In these cases it is most important that the lawn be water in April - early June so that bermudagrass puts on the maximum amount of ground cover to resist sandbur invasion. Fertilization and irrigation should be also being practiced to optimize bermuda cover in spring. 

A pre-emergent herbicide program should be used where sandburs are known to be a problem in lawns. An application of pre-emergent herbicide specifically labeled for your lawn grass should be applied at some point between late January and the first week of March. Commonly available and effective pre-emergent herbicides include Surflan, Barricade, Pendulum, XL, Team, Scott's Haults, Scott's Hault, and Dimension as well as several other brands. Consult the local garden center staff for what is available. Either granular or sprayable pre-emergent herbicides can be effective. Pre-emergent herbicides labeled for use in controlling crabgrass and goosegrass are usually effective in controlling sandbur germinating from seed. The lawn can neither be baled as hay, nor grazed by family pets or livestock if treated with a pre-emergent herbicide. Always read and follow all label directions. Pre-emergent herbicid

es need to be watered into the soil, usually within 7 days of application and certainly prior to any bagging of lawn clippings, in order for them to be effective in killing weed seeds at the time of their germination. Not watering in a pre-emergent herbicide through natural rainfall or irrigation within a week or bagging clippings containing the pre-emergent herbicide will result in ineffective weed control. Sandbur seed germination may be expected if good soil moisture becomes available in late-April through August. A second application of the pre-emergent herbicide, if allowed by the label directions, should be made in early to mid-May in order to continue to provide sandbur and grassy weed prevention well into summer. Again, don't forget to water in the second application as well, shortly after it is made.

 As most sandbur plants found in Oklahoma are the field sandbur species, it is best to bet on the problem being a short-lived perennial plant. In the year in which a sandbur lawn management program is begun, many perennial-phase plants can be expected to be present. Pre-emergent herbicides will be effective in guarding against new sandbur plants arising from seed, but these herbicides will have no effect on the perennial sandbur plants that are already present and mature in the lawn. Existing sandbur plants can be controlled with post-emergent herbicides such as MSMA and DSMA. These treatments are best administered in late May through early to mid-June. Remember, sandbur plants are tough and a diligent plan and follow-through is essential to success. MSMA and DSMA are available only as sprayable herbicide materials, they are not granular materials. The lawn can neither be baled as hay, nor grazed by family pets or livestock if treated with these herbicides.

 Usually a hand-pump up sprayer is required for applying these post-emergent herbicides. Read the product label for directions for spray applications. Typically the high-end labeled rate of these products is required for effective sandbur control. Also, 2 or more application (if allowed by the label) may be necessary. The second application is usually made about 7 but no more than 10 days after the first application. A wetting agent must also be used to help get good leaf coverage and tissue penetration of the herbicide if not already present in the herbicide pre-mix.

 Sometimes it is not feasible for the consumer to apply MSMA or DSMA for control of sandbur in their lawns and in these cases the consumer can hire a Certified Commercial Pesticide Applicator that is licensed to treat lawns in order to make these post-emergent herbicide applications. Commercial lawn care applicators can also provide a comprehensive lawn care program that aids in sandbur control. In the event that the lawn in question is a cool-season lawn, such as those containing tall fescue, Kentucky bluegrass or perennial ryegrass, neither MSMA nor DSMA can be used. In these rare cases, a Commercial Pesticide Applicator can be hired to treat the sandbur with an effective herbicide such as Acclaim Extra, which is labeled for sandbur control in cool-season lawns.