Weed Management in Alfalfa Fabián Menalled Cropland Weed Specialist 719 Leon Johnson Hall Montana State University menalled@montana.edu 406-994-4783

Weed Management in Alfalfa Integrated Management Practices Environment

Integrated Weed Management Set of cultural, mechanical, and chemical control practices to Limit the introduction and spread of weeds Help the crop compete with weeds Keep weeds "off balance"

Alfalfa Establishment Established stand Weed Management in Alfalfa Integrated Pre-Crop Alfalfa Establishment Established stand

Pre-Crop Start NOW your 2006 weed management plant “Grassy” crop in 2005 (annual summer or winter crop) Good weed control through alternative herbicides Break down the sod “Hay” Barley could be an option to maintain the forage base Control all perennial weeds the season before planting Roundup, 2,4-D, dicamba, Curtail, etc. (observe plant-back restrictions to alfalfa)

Perennial Weeds, Life Cycle

Canada Thistle Management no. / m2 Bud Stage Rosette Stage Cultivated fallow 25 Fallow + Banvel (1.05 pt/A) 16 2 Banvel (1.1 qt/A) 14 3

Perennial Weeds Management PREPLANT Roundup Ultra: many species Eptam: quackgrass, bermudagrass POSTEMERGENCE Select: foxtail barley, bermudagrass, quackgrass Buctril: Canada thistle Basagran: Canada thistle ESTABLIHED ALFALFA Kerb: foxtail barley, quackgrass, Velpar: foxtail barley, quackgrass, Sencor: foxtail barley, chickweed, dandelion, curly dock

Alfalfa Establishment Growing Alfalfa for Hay - Montguide 8505 Alfalfa Variety Selection – Montguide 9303 Alfalfa seedlings are poor competitors Seedbed should be weed free Used weed-free seeds of the highest quality

Alfalfa Establishment Weed Management Options: Mechanical: disking, cultivation Chemical Control PPI Post

Weed Management Handbook Available: December 2004 On-line Extension Publications Montana State University P.O. Box 172040 Bozeman, MT 59717-2040 406-994-3273

Eptam (EPTC) PPI 2.25 to 4.5 pt/A annual grasses broadleaf weeds Foxtails, panicum, bromus, small grains, wild oat broadleaf weeds Chickweed, pigweed, lambsquarter, purslane, carpetweed

Balan DF PPI 2-2.5 lb/A annual grasses broadleaf weeds Bluegrass, ryegrass, foxtails, panicums broadleaf weeds Chickweed, pigweed, lambsquarter, purslane,

Postemergence. Huntley, MT Weed Control (6/15/01) Treatment1 Raptor Poast Pursuit Buctril 2,4-DB 4 fl oz/A 6 fl oz/A 1.5 pt/A 3 pt/A Rate ------------------ % ------------------ 89 94 87 97 86 Kochia 91 96 95 Pigwd 93 88 Lambsq Grass2 98 51 62 1 All Raptor treatments contained COC + 32% UAN 2 Grass = composed of green and yellow foxtail and barnyardgrass

Established Alfalfa Is it worth to manage weeds? Mature alfalfa crowns can compensate for fewer plants by producing more stems or shoots per plant

Is it Worth to Manage Weeds? Select 3 to 4 two-square-foot sections (17” x 17”) Count the number of stems and divide by two 55 or more stems/ft2 = no change in yield potential with new stand 40-55 stems/ft2 = expect some yield reduction as stand declines <39 stems/ft2 = significant decline or reduction in yield – best option may be to reestablish

Herbicides Labeled for Alfalfa Sinbar – 0.5 to 1.5 lbs/A. Grassy and broadleaf weeds. Do not apply on frozen soil. Treflan - 1.5 to pts / A. Do not apply to seedling alfalfa. Velpar - 1 to 2 qts / A. Rates vary with soil characteristics. Do not graze within 30 days.

Herbicides Labeled for Alfalfa Velpar – Alfamax Combination of Diuron and Velpar (hexazinone) Dry flowable Contact and residual control One single application during winter Rates = 3.3 – 10 Acres / Unit Pack (14.2 pounds), depending on soil texture and organic matter Mustards, pigweed, chickweed, common lambsquarters Branyardgrass, cheatgrass Dry bulk fertilizer may be coated with Velpar - Alfamax Caution: can damage trees and shrubs

Downy Brome Control in Established Alfalfa Fowler Creek, Bozeman, MT Rate Alfalfa Injury Weed Control 7-May 28-Jun Velpar Alfamax 0.666 lb/a 6 96 100 1.0 lb/a 21 5 Sencor 7 94 97 Rounup UltraMax 20 oz/a 25 19 82 53 Velpar Alfamax + Karmex 0.66 + 0.75 lb/a 12 1 1.0 + 1.1 lb/a 14 99 2.0 + 2.2 lb/a 36 18

Weeds to Watch Hoary alyssum (Berteroa incana) The Prairie Star, Sept. 2004 Stevens County Noxious Weed Larimer Co., CO

Weeds to Watch Hoary alyssum Toxic to livestock Up to two feet tall Large number of seeds No Biological Control Options Mechanical Control Hand-pulling of small populations. Mowing will not control it Chemical Control Tordon + 2,4-D amine Redeem Curtail