Overview of the problem:

Since creeping bentgrass is frequently used on putting greens, tees, and fairways, escapes are not uncommon. Escapes of creeping bentgrass in our cool-season roughs create unsightly light green patches in a normally clean cut, dark green area bordering greens and fairways. Bentgrass can become established in bordering grasses from tracked and wind blown seed during establishment. Seed can also wash down slope from divot filler during rainfall. Actual plants can move with soil into roughs during core aeration and other tillage practices. This plant can also creep into surrounding areas via stolons, causing fairway lines to become distorted and uneven.

Rational for research:

There are currently no selective control options for creeping bentgrass registered in cool-season turfgrass. Control options have been limited to spot treating with a nonselective herbicide or complete renovation of infested areas. At Virginia Tech, we have looked outside the turf industry to find control options for this problem weed. Two herbicides used in crops have shown promise for selective control of creeping bentgrass in cool-season turfgrass. Isoxaflutole and mesotrione are herbicides that are used in corn for preemergence and postemergence control of several grass and broadleaf weeds. Our preliminary greenhouse and field trials indicated that mesotrione and isoxaflutole did not injure desirable tall fescue, Kentucky bluegrass, or perennial ryegrass but did control creeping bentgrass at appropriate rates. Since imazaquin (Image) has been used in warm-season turfgrass for some time and is known to be more injurious to creeping bentgrass than Kentucky bluegrass, it was also included.

Methods:

Field trials were conducted on golf course roughs at Stony Creek Golf Course near Wintergreen, VA, and Kinloch Club near Richmond, VA and on perennial ryegrass at the Turfgrass Research Center in Blacksburg, VA. Past research with other weeds using the above mentioned herbicides indicate that multiple applications will more effectively control weeds than single applications. Isoxaflutole and mesotrione were each applied at 0.25 lb active ingredient (ai)/A twice, 0.15 lb ai/A three times, and 0.05 lb ai/A three times. Imazaquin was applied at 0.50 lb ai/A once and 0.35 lb ai/A twice. Nonionic surfactant at 0.25% v/v was included with all treatments.

Results:

Creeping bentgrass plants turn white and then die following treatment of isoxaflutole or mesotrione, yet Kentucky bluegrass is typically not affected. However, at least two treatments are needed to prevent creeping bentgrass recovery following initial injury. Results indicate fall applications of all tested herbicides are more effective than spring applications for creeping bentgrass control. For example 14 weeks after treatment (WAT), all mesotrione treatments controlled creeping bentgrass less than 70% when applied in spring and near 100% when applied in fall. When applied sequentially in the fall isoxaflutole controlled creeping bentgrass greater than 90%. Mesotrione stood out not having less than 98% control when multiple applications were used. Also, Kentucky bluegrass plots treated with mesotrione and isoxaflutole were not injured. Imazaquin controlled creeping bentgrass when applied in the fall but severally injured Kentucky bluegrass.

Summary:

Based on these and several other in house trials and with collaborating researchers, mesotrione and isoxaflutole have potential for creeping bentgrass control in Kentucky bluegrass, tall fescue, and perennial ryegrass maintained at 0.5 to 4 inch mowing heights. Two or three applications at 0.25 lb and 0.15 lb ai/A, respectively two weeks apart are recommended for complete creeping bentgrass control with either product. These products should not be treated when turfgrass stress is evident. Treated creeping bentgrass turns white for a period of one to two weeks after treatment and may be a negative side affect if weed pressure is severe. Before an official recommendation can be made, these products must be registered with the US EPA. It is currently illegal to use mesotrione or Isoxaflutole in any fine turfgrass. The registration process is slow and costly. Syngenta Company, the parent company of Mesotrione 4SC, is currently seeking a registration for the turf industry. We at Virginia Tech are making every effort to provide scientific data that will allow the EPA to make an educated decision about these products.

To view more details about this research or other work, go to Dr. Askew’s web site at www.turfweeds.net and click on publications.