Weed Management in Alfalfa

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Weed Management in Alfalfa

• Fabián Menalled
• Cropland Weed Specialist
• 719 Leon Johnson Hall
• Montana State University
• menalled_at_montana.edu
• 406-994-4783

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Weed Management in Alfalfa
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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"

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Weed Management in Alfalfa

• Pre-Crop
• Alfalfa Establishment
• Established stand

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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)

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Perennial Weeds, Life Cycle
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Canada Thistle Management
no. / m2

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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

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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

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Alfalfa Establishment

• Weed Management Options
• Mechanical disking, cultivation
• Chemical Control
• PPI
• Post

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Weed Management Handbook

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

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Eptam (EPTC)

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

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Balan DF

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

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Postemergence. Huntley, MT
Weed Control (6/15/01)
1 All Raptor treatments contained COC 32 UAN
2 Grass composed of green and yellow foxtail
and barnyardgrass
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Established Alfalfa

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

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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
• lt39 stems/ft2 significant decline or reduction
  in yield best option may be to reestablish

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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.

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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

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Downy Brome Control in Established Alfalfa Fowler
Creek, Bozeman, MT
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Weeds to Watch

• Hoary alyssum (Berteroa incana)
• The Prairie Star, Sept. 2004

Larimer Co., CO
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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