1. Weed Management in Alfalfa
Fabián Menalled
Cropland Weed Specialist
719 Leon Johnson Hall
Montana State University

2. Weed Management in Alfalfa
Integrated
Management Practices
Environment

3. 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"

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

5. 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)

6. Perennial Weeds, Life Cycle

7. 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

8. 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

9. 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

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

11. Weed Management Handbook
Available: December 2004
On-line
Extension Publications
Montana State University
P.O. Box
Bozeman, MT

12. 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

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

14. 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

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

16. 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

17. Herbicides Labeled for Alfalfa
Sinbar – 0.5 to 1.5 lbs/A. Grassy and broadleaf weeds. Do not apply on frozen soil.
Treflan 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.

18. 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

19. 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
lb/a 12 1
lb/a 14 99
lb/a 36 18

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

21. 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