Weed Control for Kentucky Home Lawns G.C
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COOPERATIVE EXTENSION SERVICE • UNIVERSITY OF KENTUCKY COLLEGE OF AGRICULTURE, LEXINGTON, KY, 40546 AGR-208 Weed Control for Kentucky Home Lawns G.C. Munshaw, M. Barrett, and J.D. Green, Plant and Soil Sciences Cultural weed control Recommended time of year for herbicide applications on target weeds Season Target weeds practices—let your lawn Spring March-late April Crabgrass and other annual grasses pre-emerge control the weeds! March-May Broadleaf post-emerge1 Summer May-August Grass and grasslike post-emerge1 The best defense against weed prob- July/August Broadleaf spot treat1 lems in home lawns is a healthy and dense Autumn September/October Broadleaf post-emerge1,2 lawn. In thick lawns, weed seeds may not Winter November-January Broadleaf spot treat1 germinate because light may never reach 1 If problem weeds are present. the soil surface. A thick lawn is com- 2 Warm-season lawns (bermudagrass or zoysiagrass) may require a fall pre-emergent appli- petitive with weeds, keeping them from cation to reduce winter annual weeds in the dormant lawn. growing and reproducing. Developing a healthy and dense lawn comes from using cultural practices such as proper grass Trade names and active ingredients species and cultivar selection, proper Active ingredients mowing heights and fertilization, and Trade name Common name Chemical name1 other good management practices. The Hi-Yield 2,4-D Selective Weed Killer 2,4-D Dimethylamine salt of need for herbicides to control weeds in 2,4-dichlorophenoxy acetic acid home lawns can be greatly reduced if the Roundup glyphosate N-(phosphonomethyl)glycine lawn is well maintained. 1 The chemical name describes the chemical structure. Selecting the right herbicide can There are instances, however, when be difficult for products that list only the chemical name on the label. To determine the weeds escape and more aggressive con- contents of the product, consider cross-referencing with labels of familiar products or trol tactics are necessary. Even in well- consult your cooperative extension agent for assistance. See appendix B for a partial list maintained lawns, weeds can become of common and chemical names of ingredients of homeowner herbicides. a problem. Some weeds adapt to lawn management practices, and diseased or drought-stressed lawns can result in allows for the best timing of herbicide thin turf and create openings for weed applications on young weed seedlings. Publications detailing germination. Control tactics can in- For all weeds, herbicide treatment when healthy lawns from the clude herbicide applications or physical the weeds are young will result in the University of Kentucky removal of the weeds. In small areas, easiest and best opportunity for control or if the weed infestation is not severe, using the least amount of herbicide. Lawn Fertilization in Kentucky (AGR- physical removal is the control method of Some herbicides are packaged with a 53) at http://www.ca.uky.edu/agc/ choice. However, an herbicide application fertilizer as a “weed and feed” product. pubs/agr/agr53/agr53.htm. can provide the lawn a better chance of These products should be avoided in Turf Care Calendar for Kentucky Blue- successfully competing with weeds. the spring for cool-season lawns, which grass, Tall Fescue, and Perennial The first step if you decide to use an are composed of tall fescue, Kentucky Ryegrass Turf (AGR-55) at http:// herbicide is to know your weeds. What bluegrass, and perennial ryegrass. In www.ca.uky.edu/agc/pubs/agr/ species are you trying to control, and Kentucky it is recommended that fertil- agr55/agr55.pdf. what are their life cycles? For example, izer should not be applied to these lawns Home Lawn Irrigation (ID-79) at knowing you are trying to control smooth in the spring. Spring and summer fertil- http://www.ca.uky.edu/agc/pubs/ crabgrass and that it typically germinates izer applications lead to increased lawn id/id79/id79.htm. in early to mid-April in Kentucky gives disease and weed infestations. The best Low-Maintenance Lawn Care, Stress- you a target window to apply an herbicide time of year to fertilize cool-season lawns ing Pest Avoidance and Organic In- that kills this grass as its seeds begin to is in the fall. puts (ID-154) at http://www.ca.uky. germinate. Knowing the life cycle also edu/agc/pubs/id/id154/id154.pdf. Agriculture and Natural Resources • Family and Consumer Sciences • 4-H Youth Development • Community and Economic Development EXTENSION Types of weeds— Weeds controlled and common herbicides available at garden centers know your enemy! Annual grassy weeds—pre-emerge products The vast majority of home lawn weeds Weeds Herbicide common name Application timing in Kentucky are either annuals or peren- Crabgrass benefin + trifluralin In southern KY before April 1. In nials. Annual weeds complete their life Foxtail dithiopyr northern KY before April 15. A four-to Goosegrass pendimethalin six-week repeat application will ex- cycle—germinating, maturing, flowering, prodiamine tend control. If goosegrass is the main and setting new seeds—in one growing trifluralin target weed, apply second application season. Annual weeds can be either win- siduron1 in mid-May. ter annuals or summer annuals. Winter 1 Commonly applied during spring lawn establishment. Do not apply to bermudagrass annual weeds typically germinate during lawns. the fall, mature over the winter and early spring, and then flower, set seed and die in late spring/early summer. Summer Annual grassy weeds—post-emerge herbicides annual weeds germinate in the spring, Weeds Herbicide common name Application timing mature during the summer, then flower Crabgrass fenoxaprop1 Best results are obtained when applica- and set new seed before dying during the Foxtail quinclorac tions are made when weeds are young, fall. Perennial weeds can live for multiple Goosegrass tender, and at a rapid stage of growth. growing seasons. Some perennials are Peak germination typically occurs in earl April to early May, depending on considered cool-season or warm-season location in KY. However, annual grassy plants due to the time of year when their weeds may germinate at any time dur- growth is most prevalent. Most perennial ing the growing season. plants can reproduce both by vegetative 1 Not for use on bermudagrass lawns. structures (e.g. roots and stolons) and by seed. Biennial weeds (completing their life cycle within two growing seasons) ex- Perennial grassy weeds—post-emerge herbicides (nonselective) ist but rarely cause problems in Kentucky Weeds Herbicide common name Application timing lawns. Bermudagrass glyphosate1 Apply when target grasses are actively Weeds can be further separated Bentgrass patches fenoxaprop1,2 growing with adequate soil moisture. or classified into different groups by Dallisgrass Glyphosate will kill all species—desired their general growth habits. Grassy or Johnsongrass and undesired alike. Killed areas must Nimblewill be reseeded or resodded with desirable grasslike weeds are monocots (one leaf Orchardgrass grass. Repeated applications will be emerges from the soil). Broadleaf weeds Quackgrass required for adequate bermudagrass are dicots (two leaves emerge from the Tall fescue clumps and nimblewill control before re-estab- soil). Herbicides differ in spectrum and lishment, regardless of herbicide used. in the types of weeds that they control. 1 Glyphosate is a much more effective herbicide at controlling hard to kill weeds, such as Knowing whether you are dealing with those listed in this table. Repeat applications will likely be necessary when using fenoxa- a winter or summer annual or a peren- prop. 2 Suppresses bermudagrass. nial and whether the plant is a grassy or broadleaf weed is one of the first steps in choosing the proper herbicide control strategy. applied prior to weed seed germination bicides, usually applied post-emergent, to be effective. When seeds germinate often will injure or kill all plants within Types of herbicides— and young weed seedlings begin to grow the treated area, both desirable and un- near the soil surface, the seedling comes desirable ones that come in contact with choose the right tool! in contact with the herbicide barrier. The the herbicide. Nonselective herbicides are Herbicides available for use in home herbicide is then taken into the plant, typically reserved for spot treatments or lawn weed control can be classified by and the weed dies. Lawn grasses with total renovation of an area. when they are applied—either before established root systems are unaffected Spot treating weeds is typically per- or after weeds appear—and whether by the herbicide barrier. formed with a handheld sprayer. This they are selective or nonselective. A Selective post-emergent herbicides are method of weed control can be very ef- pre-emergent herbicide is applied before applied after weeds germinate and plants fective and uses less herbicide. However, weeds appear and controls them as the are visible. These herbicides are most ef- because non-selective herbicides will kill seed germinate. A common misconcep- fective when applied to young, actively your desired lawn species as well as the tion is that pre-emergent herbicides kill growing weeds. Most pre-emergent and weeds, the application must be carefully weeds before they germinate. Actually, post-emergent herbicides selectively controlled to keep these spots as small as pre-emergent herbicides form a residual control the undesired species without possible. barrier in the upper soil layer and must be damaging the turf. Nonselective her- 2 Reading the label—get Weeds controlled and common herbicides available at garden centers the information you need! Other grasslike weeds—post-emerge herbicides The packaging of an herbicide will Weeds Herbicide common name Application timing include the trade name of the product, Yellow nutsedge halosulfuron-methyl2 Apply when nutsedge is actively generally in large print, and the ac- sulfentrazone3 growing with adequate soil mois- bentazon ture. Yellow nutsedge will be visible tual herbicide common and/or chemical beginning in the spring/early name(s) listed in finer print under “Active summer.