CHEMICAL HOTLINE: Seedling Safety
If you're planning to plant during the summer, there are some important hints to consider that can help you meet the challenges and avoid some of the risks. Turfgrass planted in the spring or summer must compete with summer weeds, and few options exist to control these weeds while protecting the delicate nature of new, growing seedlings. Despite these difficulties, there are some potential solutions to support young turfgrass in the spring or summer months.
Some spring/summer turfgrass problems are fairly basic:
Young turfgrass seedlings are more susceptible to injury by herbicides than mature turfgrass.
Pre-emergence herbicides can prevent a successful spring turfgrass seeding.
Options for chemical weed control at or near turfgrass seeding are few.
Turfgrass managers typically limit their seeding time to the fall because few options exist to control weeds during seeding for warm- or cool-season grasses. For example, bermudagrass, a common warm-season grass, is tolerant to oxadiazon at sprigging, but not during seeding. Summer annual grasses (e.g. crabgrass, foxtail, panicum, etc.) and broadleaves (e.g. common lambsquarters, ragweed, pigweed, etc.) may germinate and overpower seeded turfgrasses during the spring and summer months. These weeds are not a factor when you seed in the fall. However, you don't always have the luxury of waiting for the fall season to seed problem areas or complete new construction.
Until recently, spring seeding of cool-season grasses was also a problem due to limited weed-control options and increased weed pressure following spring tillage. The only pre-emergence weed-control option for spring-seeded cool-season grasses (e.g. creeping bentgrass, fescue, perennial ryegrass and Kentucky bluegrass) was siduron. Siduron controls crabgrass, foxtails, downy brome and barnyardgrass, and makes turfgrass-stand establishment possible. However, siduron does not control broadleaf weeds and many problematic grasses such as goosegrass and fall panicum. The limited options previously available caused turf managers to avoid spring and summer seeding because they generally lost the war against weeds.
PREBATTLE: PRE-EMERGENCE CONTROL OPTIONS
Pre-emergence weed-control options offer a real solution for spring and summer seeding because they eliminate the weed competition that severely limits turfgrass establishment. By controlling weeds at turfgrass seeding, you can hasten the establishment of new turf and possibly eliminate the need for subsequent postemergence chemical treatments.
In addition to siduron, quinclorac is the only other herbicide currently registered for weed control at turfgrass seeding. Quinclorac has been used primarily for postemergence crabgrass and clover control. However, the potential of this herbicide for use at turfgrass seeding has largely been overlooked. You can use quinclorac at seeding of annual bluegrass, annual ryegrass, buffalograss, common bermudagrass, hybrid bermudagrass, perennial ryegrass, tall fescue and zoysiagrass. You can also use quinclorac seven days prior to seeding of creeping bentgrass, fine fescue and Kentucky bluegrass. In addition, you can use it anytime prior to, at, or after sprigging of common bermudagrass, hybrid bermudagrass or zoysiagrass.
By comparison, you can apply siduron at seeding of creeping bentgrass, colonial bentgrass, tall fescue, Kentucky bluegrass and perennial ryegrass. However, you should not use siduron at seeding or sprigging of warm-season grasses such as bermudagrass. You may use oxadiazon at sprigging of common bermudagrass and hybrid bermudagrass, but not at seeding of any turfgrass. Most grassy weed herbicides used on turfgrass must be applied at least three weeks before turfgrass can be seeded. A few exceptions include fenoxaprop, bentazon, bromoxynil and ethofumesate. However, with the exception of ethofumesate, these herbicides do not control weeds at the preemergence stage. Of course, turfgrass susceptibility to herbicide injury varies with turfgrass species, and generalizations are difficult to make. Always consult the herbicide label before using any product prior to turfgrass seeding.
IN THE TRENCHES: POSTEMERGENCE CONTROL OPTIONS
- Grassy Weeds
A good rule of thumb is to wait until the fourth mowing or at least one month after emergence to treat newly seeded turfgrass with a selective herbicide. There are only a few chemicals you can use within this time frame.
You can control most annual grasses postemergently with fenoxaprop, quinclorac and MSMA in young turfgrass. You can use fenoxaprop at reduced rates on turfgrass seedlings that are at least four weeks old. Delay treatment of MSMA until the third mowing. You can apply quinclorac seven days after emergence of annual bluegrass, annual ryegrass, buffalograss, common bermudagrass, hybrid bermudagrass, tall fescue and zoysiagrass. Other turfgrass species, including creeping bentgrass, fine fescue, Kentucky bluegrass and perennial ryegrass, can be treated with quinclorac 28 days after emergence.
Common name Trade name (supplier) Bentazon Basagran T/O (TopPro) Lescogran (LESCO) Nutgrass 'Nihilator (Monterey) Bromoxynil Bromox 2E (Micro Flo) Buctril (Aventis) Clopyralid Lontrel T&O (Dow AgroSciences) 2,4-D AM-40, 2,4-D Granules, 2,4-D L. V. Ester, Solution (Riverdale)Dymec (PBI/Gordon) Weedone LV4 (Aventis) Dicamba Banvel (Micro Flo) Oracle (Agrisel) Vanquish (Syngenta) Dithiopyr Dimension (Andersons, Best/Simplot, Dow AgroSciences Howard Johnson's, Lebanon) Dimension 270-G (Best/Simplot) Dimension Ultra (Dow AgroSciences) Ethofumesate Prograss (Aventis) Fenoxaprop Acclaim Extra (Aventis) Foramsulfuron Revolver (Bayer) Halosulfuron Manage (Monsanto) MCPP (Mecoprop) Chem-weed (Opti-Gro) MCPP-4 Amine (Riverdale) MCPP-4K (UHS) Mecomec (PBI/Gordon) Oxadiazon Ronstar (Bayer) Pendimethalin Pendiflex 32 (Agrisel USA) Pendulum (BASF) PRE-M (LESCO) Corral, ProPendi (Andersons/ProTurf) Prodiamine Barricade (Syngenta) RegalKade (Regal) Quinclorac Drive (BASF) Rimsulfuron TranXit (Griffin L.L.C.) Siduron Tupersan (PBI/Gordon) Super Tupersan (Rockland) Tupersan 4.6% (Lebanon) Triclopyr Turflon Ester (Dow AgroSciences, Monterey)
Quinclorac controls weeds postemergently in young turfgrass and also controls many emerged broadleaf and grassy weeds, as well as provides preemergence control of some broadleaf weeds and grasses, such as crabgrass and foxtail. Quinclorac does not control goosegrass, prompting special consideration in goosegrass-infested areas. Goosegrass is best controlled preemergently by treating with a residual herbicide such as dithiopyr or prodiamine after the second turfgrass mowing. If goosegrass has already emerged prior to the second mowing, you can use fenoxaprop at four weeks after emergence and MSMA after the third mowing.
Fenoxaprop, quinclorac and MSMA do not control annual bluegrass. You should apply a residual herbicide such as dithiopyr, pendimethalin or prodiamine in late August after the fourth turfgrass mowing for preemergence annual bluegrass control. Ethofumesate is the only selective herbicide for postemergence annual bluegrass control in cool-season turfgrass. Apply ethofumesate during the peak of annual bluegrass germination and again just before winter. You can apply ethofumesate anytime before, at or after seeding tall fescue; two weeks after perennial ryegrass emergence; and eight weeks after Kentucky bluegrass emergence. An additional spring treatment of ethofumesate may be warranted where substantial spring annual bluegrass germination occurs.
In bermudagrass, you can apply rimsulfuron and foramsulfuron up to 14 days prior to perennial ryegrass overseeding for postemergence and residual annual bluegrass control.
- Broadleaf Weeds
Control broadleaf weeds with products that contain active ingredients such as 2,4-D, dicamba, clopyralid, MCPP and triclopyr in various combinations. Most of these products require that turfgrass be “well established” or mowed at least twice before treatment. During this time, broadleaf weeds can compete with turfgrass seedlings and reduce turfgrass stand establishment. In several Virginia field studies, quinclorac controlled or suppressed many broadleaf weeds when applied at turfgrass seeding and seemed to reduce broadleaf weed competition during turfgrass establishment. Siduron does not control broadleaf weeds, prompting subsequent treatment with a broadleaf herbicide. Quinclorac is also effective as a postemergence treatment for some broadleaf and grass weeds, especially clover.
Control nutsedge, annual sedges and kyllinga in most turfgrass species with halosulfuron, MSMA and bentazon. You can seed turfgrass two weeks after treating with any of these chemicals. Emerged turfgrass must be well established and have a well-developed root system before you treat it with halosulfuron or bentazon. You can apply MSMA after the third turfgrass mowing. Halosulfuron will control most sedge species while MSMA and bentazon only control annual sedges and yellow nutsedge. Sedge control, particularly with MSMA or bentazon, usually requires multiple chemical treatments.
If you plant before the fall this year, careful selection of an appropriate turfgrass species and the right herbicide can impact your success. By knowing your weed control options and following label directions, you can effectively and safely control weeds before, during, and after your planting.
Dr. Shawn Askew is an assistant professor and extension turfgrass weed scientist at Virginia Polytechnic Institute and State University (Blacksburg, Va.).
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