Several new herbicide active ingredients and combination products have been introduced to the market during the past few years. Perhaps most notable was Imprelis. However, sales of the product were suspended in August 2011 due to concerns about possible nontarget injury on pines, spruces and other ornamental species. It was unclear at the time of this writing if, or when, Imprelis would again be made available for use on turfgrass.
White clover is an example of a perennial broadleaf weed. It and other perennials can be controlled in the springtime. However, control is better and for a longer duration if herbicide applications are made to perennial broadleaf weeds in the fall.
PHOTOS COURTESY OF D.S. GARDNER.
There have been many other herbicides introduced for broadleaf weed control in the past few years. In fact, the number of active ingredients registered for broadleaf weed control in turfgrass has doubled since 2000. This article will review those newer herbicides that can be used on both cool and warm-season turfgrasses. Always consult the label prior to use to verify that the product is safe for your type of turf.
This new active ingredient will be marketed as Defendor from Dow AgroSciences. It became available in a co-pack with Dimension 2EW in December 2012. Defendor can be used safely on all major turfgrasses and should be applied at typical preemergence crabgrass timing. To prevent dandelion flowering, application should be made prior to dandelion bloom. Weeds controlled include dandelion, white clover, common and mouse-ear chickweed, mustard and shepherd’s purse.
Research conducted at The Ohio State University shows that a single application of Defendor herbicide will give greater than 90 percent control of both dandelion and clover for 84 days. On plots receiving sequential applications (42 days apart) control was still nearly 100 percent 98 days after the initial application.
Fiesta herbicide contains a proprietary chelated iron that, when applied to turf, acts as a selective postemergence herbicide against a wide spectrum of broadleaf weeds. Control is very rapid, with nearly 100 percent burn down achieved, often within 24 hours. It is important to note that this is a contact herbicide.
Preliminary results at The Ohio State University suggest that when using this product to achieve long-term weed control, the total amount of Fiesta applied over a season is at least as important as the schedule of the applications. Best results thus far have been with three applications of an 8 percent solution applied at 2.5 gallons per 1,000 square feet at 21-day intervals. This has resulted in excellent control of dandelion, white clover and ground ivy and good control of broadleaf plantain for up to 70 days. Since burn down is so rapid, the amount of control is actually longer than with a traditional herbicide that might take up to 28 days to achieve control.
This product is legal to use in Canada, where there is a ban on pesticide use in turf, and will be an important tool for turfgrass managers in locations in the U.S. that are under similar restrictions. The product can discolor the turfgrass by turning it dark green or even black if used in hot weather. Because of this, it should be used in cooler weather (50 to 65 degrees Fahrenheit) to reduce the potential darkening of the turfgrass.
Mesotrione is a newer herbicide introduced by Syngenta under the trade name of Tenacity. Note that this herbicide is not safe for warm-season turfgrasses with the exception of dormant bermudagrass. Mesotrione is effective both pre and postemergence against dandelion, white clover, crabgrass, creeping bentgrass, and many other grass and broadleaf weeds.
As a broadleaf herbicide, Tenacity has good activity against dandelions and fair activity against clover. A second application is required in order to control certain weeds; otherwise one application will result in suppression of the weed, followed by regrowth in about 42 to 56 days.
You can also improve control by combining Tenacity with another chemistry. Our research indicates that Tenacity has better activity when combined with dicamba, fluroxypyr or triclopyr. Our research also suggests that mesotrione does not combine well with Quicksilver, Dismiss or the phenoxy herbicides such as 2,4-D for broadleaf weed control. Tenacity also can be used pre and post-emergence for control of crabgrass, on newly seeded turfgrass, and for the control of perennial grasses such as creeping bentgrass.
Marketed as Dismiss herbicide, sulfentrazone is in the same class of chemistry as carfentrazone. However, sulfentrazone is thought to have more soil activity in addition to being a contact material like carfentrazone. It is an excellent herbicide for control of yellow nutsedge. Sulfentrazone is also a component of the products Echelon (along with prodiamine), Q4 (along with 2,4-D, dicamba and quinclorac) and Solitare (along with quinclorac).
Echelon has some activity against broadleaf weeds and sedges. However, its best use is for pre and early to mid-postemergence control of crabgrass. Solitare has good postemergence activity on dandelion, clover, ground ivy, nutsedge and crabgrass.
This herbicide was released in 2008 by SePro under the trade name Octane. Similar to carfentrazone and sulfentrazone (Quicksilver and Dismiss, respectively), pyraflufen ethyl is a protox inhibitor and a fast-acting contact herbicide. Like Quicksilver and Dismiss, it is intended for use in a tank mix with other herbicides to control perennial broadleaf weeds like dandelion and clover. When used in tank mixes it results in faster burn down of weed tissue without affecting long-term control.
Octane can also be used when establishing turfgrass from seed. Consult the label for specifics. Also, this product can be used as a stand-alone herbicide against young summer annual broadleaf weeds, such as knotweed, spurge and black medic.
Dow AgroSciences is marketing this herbicide under the trade name LockUp. It is currently being sold in the South as an atrazine replacement. It is sold as a single entity product and not in combination. There are no plans for a stand-alone product in the cool-season turf market. However, LockUp in combination with 2,4-D and 2,4-D + dicamba is for sale in cool-season turfgrass markets. It is formulated as a granular product.
Research at Ohio State indicates that penoxsulam, especially when combined with 2,4-D and/or dicamba, provides good control of dandelions and excellent control of white clover when used in early spring.
Many new combination products have been formulated in an attempt to control both broadleaf weeds and grassy weeds postemergence with a single application. Some of these products will also control yellow nutsedge. Quinclorac is of course not new, but increasingly quinclorac is appearing in combination products, not just for crabgrass control, but also for broadleaf weed control, particularly clover.
Products that control both crabgrass and broadleaf weeds include Quincept (2,4-D, dicamba, and quinclorac), Onetime (MCPP, dicamba and quinclorac) and Q4 (2,4-D, dicamba, sulfentrazone and quinclorac).
Knotweed (which can look like crabgrass when it first germinates) is an example of a summer annual broadleaf weed.
Springtime turfgrass establishment from seed has always been a challenge because of competing weed pressure, particularly crabgrass. However, SquareOne, which combines quinclorac and carfentrazone, is labeled for and can be effective when establishing turfgrass from seed.
Newer combination products
There are many combination herbicides registered for use on sports fields. Table 1 provides a summary of those combination products that can be used on both cool and warm-season turfgrass. Some of the most recent additions to this list include 4 Speed (2,4-D, MCPP, dicamba and pyraflufen), 4 Speed XT (2,4-D, dicamba, triclopyr and pyraflufen) and T-Zone (2,4-D, dicamba, triclopyr and sulfentrazone). Each provides excellent control of broadleaf weeds.
Turfgrass managers typically apply broadleaf herbicides in the spring to control weeds such as dandelion, white clover and the plantains. Ironically, this can result in large, bare patches that are filled in by annual grasses, such as crabgrass, and annual broadleaf weeds, like spurge. In addition, weed control tends to be less effective with springtime applications. Dandelions, white clover and several other key sports field weeds are perennials. That is, they persist from year to year via an underground storage structure that may or may not include a taproot.
It is probably not possible or practical to delay control of dandelions and other perennial weeds until November. However, fall always has been, and will continue to be, the best time of year to control perennial broadleaf weeds. Fall herbicide applications offer several advantages over springtime applications. Most annual ornamental plants and vegetables have reached maturity, and leaves of trees and shrubs are beginning to turn color and fall off the plant, so the chance of nontarget injury due to drift is greatly reduced. Also, winter annual weeds such as henbit and common chickweed are controlled if the application is done after they germinate. However, the major advantage of fall applications is effectiveness of control.
Table 1. Broadleaf herbicide combination products that are labeled for use in both cool and warm season turfgrass. Always consult the label prior to use.
Perennial weeds typically generate new vegetative growth in the early spring, flower in late spring or early summer, and then persist into fall. During the spring, when the weed is generating new vegetative growth, it uses carbohydrates stored over winter in the underground storage structures. To bring these materials to the generating leaves, the plant translocates the carbohydrates from below ground upward. In order to get effective control the herbicide must translocate throughout the root system and the underground structures. If you apply herbicides in the spring, they must move against this upward translocation stream. Spring applied herbicides are almost never as effective as they could be, because the herbicide can’t as effectively reach all of the belowground structures of the weed. During the fall, the weed begins to store carbohydrates for the winter and for next year’s growth. When this occurs, the translocation stream is downward. Herbicides applied when the plant is actively translocating carbohydrates underground are also more effectively moved into the roots and storage structures, resulting in better overall control of belowground structures.
In most situations you will encounter annual and perennial broadleaf weeds in the same turf stand. However, in rare instances in a mature turf (or if you are seeding a field), you may encounter a turf area with annual broadleaf weeds only. If this is the case, then fall application of herbicides are probably not warranted since annual weeds are at the end of their life cycle. The only situation in which you would target annual weeds in the fall is if their cover is so great as to interfere with good growth of the turfgrass. Annual broadleaf weeds and annual grassy weeds are more appropriately controlled using preemergence herbicides applied in the spring. If, however, you encounter a significant percentage of perennial weeds, then fall is the best time to spray.
The key to maximizing control of perennial broadleaf weeds is to apply the right herbicides at the right time of year. You should also consult the label to determine if the addition of a surfactant is warranted. The best time to apply herbicides is generally around the same time that the last mowing and fertilization of the year occur. Daytime air temperatures should be consistently in the 40s and 50s. Many university trials have proven that the best control of perennial broadleaf weeds occurs if they are sprayed at this time.
There are a couple of things to remember about late-fall herbicide applications. The plant is not metabolizing as quickly, and you will not see the dramatic burn down and twisting (epinasty) that you normally see with an application in warmer weather. While it may not appear as though the application was effective, if you return to that spot next spring the weed will be dead and not returning.
Also, most broadleaf herbicides come in either amine or ester formulations. This is true of the phenoxy herbicides, including 2,4-D and MCPP, and the pyridinoxy herbicides such as triclopyr. The ester formulation tends to penetrate the weed tissue better, resulting in more complete control. This is especially true as temperatures cool in the fall. Ester formulations should be your choice when spraying in temperatures below 60 degrees. The caveat to esters is that they are very volatile and should be avoided when temperatures are warmer than 65 to 70 degrees. Remember that postemergence herbicides are most effective if applied during sunny weather with no rainfall within 24 hours of application.
Dave Gardner is an associate professor in the department of horticulture and crop science at the Ohio State University. He teaches courses in turfgrass management, ornamental plant identification and statistics. His research focuses on turfgrass physiology and weed management.