Tenacity, with a novel new active, adds to the list of newer, exciting broad-spectrum herbicides

Lawn care professionals have many new or relatively new options for weed control. The flow of novel active ingredients, combo products and label amendments from major specialty chemical suppliers continues unabated.

In the untreated controls there was as much as 70 percent crabgrass, purslane and yellow nutsedge. The plots where 8 ounces of Tenacity were applied, however, were 95 to 99 percent perennial ryegrass and weed-free.

Here’s a list of some of the most popular herbicides introduced in the last four or five years: Drive XLR8 from BASF, Celsius from Bayer Environmental Science, Katana and Q4 Plus from PBI Gordon, Quincept from Nufarm Americas, Inc., and Solitare from FMC Professional Products.

Each of these products possesses unique characteristics, making it more suitable for specific uses on selected properties than competing products. Obviously, it’s up to turfgrass pros to research and evaluate each herbicide’s effectiveness in controlling the particular weeds that challenge their clients’ properties, be it residential lawns, commercial properties or sports fields.

One of the newest products on the market is Tenacity herbicide from Syngenta. It was registered for use on golf courses and sod farms in 2007. It has since been registered for use on sports fields and home lawns. The active ingredient is mesotrione that has perhaps the widest weed control spectrum of any herbicide used in turfgrass, according to research conducted at The Ohio State University. It has a very distinctive mode of action. It inhibits carotenoid pigment synthesis and results in a bleaching of the affected tissue, which causes the target weed to turn white.

Tenacity has many potential uses for the lawn care industry and sports fields. However, the label limits application to 16 ounces per acre per year, meaning two 8-ounce applications or three 5-ounce applications. Therefore, some thought should be given to how and when to use Tenacity in order to maximize its effectiveness.

One of the difficulties that turf pros face when establishing turf from seed is competition from weeds. Prior to the introduction of Tenacity, there were two products labeled for control of weeds in newly seeded cool-season turf: siduron and bromoxynil. Neither of these products is as effective as other herbicides used in cool-season turf, but their safety to turfgrass seedlings makes them good options.

Tenacity has excellent safety on Kentucky bluegrass, perennial ryegrass and tall fescue. In fact, research conducted at The Ohio State University shows that Tenacity can be applied at seeding and results in no visible injury beyond seven days after emergence nor any reduction in establishment rate.

Some phytotoxicity has been reported when repeated applications are made to perennial ryegrass. This problem can be minimized by applying it in cooler weather and also by avoiding making sequential applications too close together. (Make applications 21 days apart on ryegrass and 14 days apart on bluegrass).

Tenacity has preemergence and postemergence activity against a broad spectrum of broadleaf weeds. In most cases, a second application may be needed in order to achieve complete control of broadleaf weeds. Otherwise, one application will generally result in suppression of the weed, followed by re-growth in about 42 to 56 days.

Dandelion is, however, an exception. Research at Ohio State suggests that you can expect about 70 to 85 percent control with either one or two applications. Research there also indicates that Tenacity has better activity on broadleaf weeds when combined with either dicamba or the pyridinoxy herbicides fluroxypyr or triclopyr. Tenacity has activity on clover. However, this is more suppression than control, particularly if only one application is made. Improved control is possible by combining pyridinoxy herbicides or dicamba with Tenacity.

Research conducted at OSU suggests that you may achieve nearly 100 percent control of crabgrass for up to 160 days when Tenacity is used in combination with a product such as prodiamine. Since Tenacity has both preemergence and postemergence activity on crabgrass, you can apply the combination of Tenacity and prodiamine to emerged early stage crabgrass (up to one to two tiller) and still get good control. Note this longevity of control if any overseeding projects are planned for late summer or early fall since prodiamine has a long residual and isn’t safe to seedling turfgrass.

Tenacity turfgrass herbicide resulted in rapid, easy-to-visualize reductions in troublesome weeds in turfgrass trials at The Ohio State University.

Finally, OSU’s research suggests that mesotrione’s activity on crabgrass when applied mid- to late postemergence is at least as good as, and occasionally better than, that of quinclorac or fluazifop.

Quinclorac products

Quinclorac is a unique herbicide for grassy and broadleaf weed control that has been used for several years in turf as Drive 75 DF. Drive XLR8 from BASF is a newer liquid formulation with 1.5 pounds of quinclorac per gallon. Both Drive formulations effectively control crabgrass, foxtail, clovers, torpedograss and other broadleaf weeds in certain warm-season and cool-season turfgrasses. Since quinclorac is compatible in tank-mixtures with growth regulator herbicides, combination products containing quinclorac and other active ingredients have been released for use in turf.

Combo products broaden control

Onetime (quinclorac, dicamba and MCPP) from BASF, Quincept (2,4-D, quinclorac and dicamba) from Nufarm Americas, Q4 Plus (quinclorac + sulfentrazone + 2,4-D + dicamba) from PBI Gordon, and Solitare (quinclorac + sulfentrazone) from FMC Professional Products are relatively new combination herbicides that provide excellent broadleaf weed control with activity on grassy weeds.

Onetime, a fast-acting, liquid, postemergance herbicide launched by BASF five years ago (quinclorac, dicamba and MCPP) provides a better spectrum of broadleaf weeds controlled than Drive alone. BASF says the product can be used on cool-season and warm-season grasses.

Quincept from Nufarm Americas, Inc. (2,4-D, quinclorac and dicamba) was introduced about two years ago. Its mode of action is a synthetic auxin growth regulator. It controls crabgrass, barnyardgrass, signalgrass, foxtail and about more than 200 broadleaf weeds, says the company. The product can be used in the spring as a cleanup product for areas that missed a preemerge grass herbicide application or late season for weed escapes.

Q4 Plus (quinclorac + sulfentrazone + 2,4-D + dicamba) from PBI Gordon was designed to replace Trimec Plus that contained MSMA. PBI Gordon says Q4 Plus has dramatically less discoloration on cool-season turf compared to MSMA, which is now disappearing from the market.

Q4 Plus controls most troublesome weed species, including crabgrass, foxtail and yellow nutsedge, in cool-season and bermudagrass turf areas. The company says it offers fast visual response with a wide window of application for broadleaf weeds, and rapid activity and death of broadleaf weeds.

Solitare (quinclorac + sulfentra- zone) is a dual-action postemer- gence herbicide from FMC designed to manage any combination of crabgrass, sedges and broadleaf weeds in a single application.

FMC says that Solitare, formulated as a dispersible granule, stops the formation of vegetative reproduction structures, reducing the capability of reproduction for the remainder of the season and into the following season. It also impacts viability of seeds within the soil, helping to decrease weed populations this season and the next. The product works by foliar contact to stop photosynthesis and provide fast, visible results on weeds, and is also absorbed by plant roots and translocated through its vascular system.

T-Zone (triclopyr + sulfentrazone + 2,4-D + dicamba), introduced by PBI Gordon three years ago, is for postemergence broadleaf weed control in cool-season turfgrass. T-Zone has activity on numerous broadleaf weeds and may be used for residential turf, sod farms, golf courses, sports facilities, non-croplands and other institutional sites.

Bermudagrass, bahiagrass and zoysiagrass may be treated during full dormancy at 2 to 2.25 pints per acre, says the company. Dormant applications to warm-season turfgrasses are recommended due to the presence of triclopyr in this product.

Warm-season weed fixes

Blindside (sulfentrazone + metsulfuron) from FMC Professional Solutions is a postemergence herbicide to control difficult weeds, such as doveweed, dollarweed, buttonweed and sedges in warm-season turfgrass, even St. Augustine. It’s also approved for use on Kentucky bluegrass and tall fescue, providing transition zone flexibility. Do not use it on seashore paspalum or bahiagrass.

FMC says the herbicide, available as a dispersible granule, can be applied at warmer temperatures without causing additional stress to turf. The company says that it causes visible signs of control within a week, but also has extended soil activity causing a significant reduction of weeds the following season.

Celsius (thiencarbazone + iodosulfuron + dicamba) from Bayer is a combo product for postemergence weed control. Celsius (68 WDG) is labeled at 2.5 to 7.4 ounces of product per acre for use in common and hybrid bermudagrass, buffalograss, centipedegrass, St. Augustinegrass and zoysiagrass with activity on numerous annual and perennial broadleaf weeds.

Thiencarbazone and iodosulfuron are two newer active ingredients in turf while dicamba is an older chemistry used for broadleaf weed control. Celsius is intended for commercial use by licensed applicators on residential lawns, golf courses, sports fields, parks, sod farms and other turf areas.

Celsius is applicable on southern lawns with mixed turf species, such as centipedegrass and St. Augustinegrass, where other control options have been limited due to differential species tolerance to herbicides, reports Dr. Patrick McCullough, extension turf weed scientist, University of Georgia. However, bahiagrass and seashore paspalum are sensitive to applications and Celsius will not be applicable if these grasses are considered desirable species.

Preliminary university experiments with Celsius have also shown activity for crabgrass control. However, this activity appears to be limited to young populations of large crabgrass only, says McCullough.

Katana (flazasulfuron) is a sulfonylurea herbicide from PBI Gordon that became available in spring 2010 for use in bermudagrass, centipedegrass and zoysiagrass. It received registration for use in California this past May. Katana, formulated in a 25 percent dry flowable formulation, has postemergence activity on numerous broadleaf and grassy weeds including clovers, dandelion, common chickweed, perennial ryegrass, annual bluegrass and tall fescue

Katana also controls annual sedges, yellow nutsedge, purple nutsedge and several Kyllinga species. In preliminary experiments, repeat applications of 0.5 ounce of product per acre completely controlled purple nutsedge and perennial Kyllinga, similar to halosulfuron (SedgeHammer). Katana will likely have similar turf species limitations and uses in weed control programs similar to trifloxysulfuron (Monument) but with a greater spectrum of broadleaf weeds controlled, reports McCullough.

With weed challenges differing from region to region and, in many cases, property to property, turf pros are fortunate to have so much chemistry at their disposal. By staying informed of research at their nearest land grant university they’ll be better able to make informed and appropriate product choices.

David Garnder, Ph. D., is associate professor horticulture & crop science, The Ohio State University, and is a technical advisor to Turf magazine. Ron Hall is editor-in-chief of Turf magazine, and has been an editor in the green industry for the past 28 years. You can contact him at