Most read Forage Types articles
|Herbicides for spring weed control in alfalfa|
|Tuesday, 11 May 2010 14:56|
The following article was written by William Curran and Dwight Ligenfelter, Penn State Weed Science. View the article, as well as additional information, from the March 9 edition of Penn State Field Crop News.
As warmer weather approaches, alfalfa is starting to break dormancy! It’s time to check the need for weed control. Keep in mind all of these herbicides are labeled for use in pure—stand alfalfa. However, only metribuzin and Pursuit can be applied to established alfalfa-grass mixes. Here are a few guidelines about available products:
Gramoxone Inteon 2L (paraquat) — May be applied at 2 to 3 pt/A to established “dormant” stands before 2 inches of spring regrowth. The weeds must be actively growing at the time of application. Gramoxone is also labeled at 1 to 2 pt/A for dormant application on new fall seeded stands. Gramoxone will desiccate any green tissue including actively growing alfalfa. Be especially cautious with new fall seedings. Gramoxone is effective on low to moderate infestations of winter annuals including chickweed, henbit, deadnettle, and mustard species. If winter annual weed infestations are severe, consider one of the soil active alternatives. Do not use on mixed stands.
Poast Plus 1E (sethoxydim) — Poast Plus controls annual grasses and suppresses perennial grasses in seedling and established alfalfa. Apply Poast Plus at 1.5 to 2.5 pt/A to actively growing grassy weeds. Poast Plus should be applied to small grasses and performance improves with warmer temperatures. Do not use on mixed stands.
Prowl H2O 3.8CS — has a supplemental label for use in seedling and established alfalfa. For seedling alfalfa (2-trifoliate to six inches tall), apply Prowl H2O at 1.1 to 2.1 pints pt/A prior to weed emergence. For established stands (i.e., alfalfa that was planted in fall or spring and has gone through a first cutting/mowing), apply 1.1 to 4.2quarts/A prior to weed emergence.
Applications can be made in the fall after the last cutting, during winter dormancy, or in the spring before alfalfa reaches 6 inches of regrowth and weeds have germinated. Prowl H2O will control many annual grasses and broadleaves including crabgrass, panicums, foxtails, lambsquarters, pigweed at the 1 to 4 pt rate. Other weeds such as annual bluegrass, common chickweed, dodder, henbit, prostrate knotweed, smartweed, and velvetleaf can be controlled with the 2 to 4 qt rate. Some stunting and yellowing to the alfalfa may occur after application. Do not harvest alfalfa less than 28 days after applying ≤2.1 quarts/A, or less than 50 days if >2.1 quarts/A.Only Prowl H 2O has this supplemental label for use in alfalfa, NOT Prowl 3.3EC.
Pursuit 70DG (imazethapyr) — Pursuit may be used for weed control in seedling (2 trifoliates or larger) or established alfalfa. Apply Pursuit at 1.08 to 2.16 oz/A plus adjuvants to actively growing weeds 1 to 3 inches in height. Pursuit performance improves with warmer temperatures. If spraying during extended cold periods, expect weeds to respond slower or the herbicide can have reduced activity. Pursuit is effective on many winter annual broadleaves including small chickweed. Pursuit may be used on established alfalfa-grass mixtures.
Raptor 1AS (imazamox) — Raptor may be used for weed control in seedling or established alfalfa. Apply Raptor at 4 to 6 fl oz/A plus adjuvants to small, actively growing weeds and to established alfalfa in the fall or in the spring. Any application should be made before significant alfalfa growth or regrowth (3 inches) to allow Raptor to reach the target weeds. Like Pursuit, Raptor performance is influenced by temperature. Therefore, try to apply the herbicide on warmer days and when weeds are actively growing. Raptor has a similar spectrum of winter annual weed control as Pursuit. Do not use on mixed stands.
Select 2EC (clethodim) — Apply Select at 6 to 8 fl oz to actively growing grasses that are less than 6 inches tall. Rates up to 16 fl oz may be used to control larger grasses, annual bluegrass or perennials such as quackgrass. Include a crop oil concentrate in the spray mixture. May be tank-mixed with Pursuit, Buctril, or 2,4-DB for broadleaf weed control. Do not use on mixed stands.
Metribuzin 75DF (formerly Sencor) — May be used on established alfalfa. Apply 0.5 to 1 lb/A before spring regrowth. Impregnation on dry fertilizer can improve crop safety and allow for slightly later applications (up to 3 inches spring regrowth). Sencor controls winter annual broadleaves and grasses (higher rates for grass control). May be used on mixed alfalfa-grass stands. Higher rates can potentially cause a reduction in grass stand.
Velpar 2L (hexazinone) — Apply Velpar to established alfalfa at 2 to 6 pt/A during the dormant period before 2 inches of spring regrowth. Velpar is effective on annual broadleaves and grasses. Velpar is the most effective dormant season treatment for suppression of dandelion and dock species (higher rates for grasses and perennial suppression). Do not use on mixed stands.
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