Weed management in alfalfa

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  • 1. Weed management in alfalfa
    Mark J. Renz
    mrenz@wisc.edu
    University of Wisconsin-Madison
  • 2. Costs of weeds in forages
    • Risk of establishment failure
    • 3. Reduction in biomass of desirable plants (FEED)
    • 4. Reduction in quality of feed
    • 5. Affect animal health
    Poison
    Reduced feeding
  • 6. Impact of Common Weeds on Forage Quality
    SERIOUS MODERATE SLIGHT
    ANNUAL WEEDS .
    YELLOW FOXTAIL GREEN FOXTAIL COMMON RAGWEED
    GIANT FOXTAIL VELVETLEAF PIGWEED SPECIES
    GIANT RAGWEED SHEPHERD’S PURSE
    SMARTWEEDS PENNYCRESS
    COCKLEBUR LAMBSQUARTERS
    NIGHTSHADES WILD MUSTARD
    PERENNIAL WEEDS .
    CURLY DOCK CANADA THISTLE DANDELION
    HOARY ALYSSUM QUACKGRASS WHITE COCKLE
    YELLOW ROCKET
  • 7. Weed Management in the Establishment Year
    • Weed management decisions should be based on
    weed species
    weed density
    soil moisture
    IFweed density is moderate to low
    AND soil moisture is adequate
    THEN successful establishment
  • 8. Methods of establishing alfalfa
    • Direct seeding
    • 9. Spring
    • 10. Late summer
    • 11. Seeding with a companion crop
  • Reduction in alfalfa plant density from weed competition
  • 12. Reduction in alfalfa plant density from weed competition
  • 13. 55 stems/square foot= 4-5 plants/square foot
  • 14. Goal is for >30 plants/square foot by fall
  • 15. Effects of seeding rate when don’t control weeds
  • 16. Summary for establishment effects on alfalfa density
    Weeds can reduce stand density
    Be careful especially if planting
    Planting lower alfalfa densities
    Have high weed pressure
    Competitive weeds species in field
    Dry conditions that reduce alfalfa emergence
    Management can alleviate some of the loss
    Many tools available
    Allow for scouting and POST application
  • 17. When should we manage weeds in Alfalfa?
  • 18. Critical period Period of time after crop emergence that will not have yield reduction if weeds are removed
    % alfalfa yield (vs no weeds)
  • 19. Critical period
    Note can change if more weeds!
    % alfalfa yield (vs no weeds)
  • 20. Results
    • Critical period varied by location but ranged between 1st and 7thtrifoliate leaf
    • 21. 3-5 weeks after planting
    • 22. 1-5 weeks after planting
    • 23. Same period was found for first harvest and first year yield of ALFALFA ONLY
    • 24. Higher weed density caused critical period to begin earlier
  • What effect will weed management have on forage yield and quality?
  • 25. Yield changes from weed removal
  • 26. Yield changes from weed removal
  • 27. Yield differences in establishment year5 states including Wisconsin
  • 28. Forage quality (RFV) changes from weed management
    Can reduce RFV below recommendations for Dairies
    Depends on the weed species and weed density!
  • 29. Impact of Common Weeds on Forage Quality
    SERIOUS MODERATE SLIGHT
    ANNUAL WEEDS .
    YELLOW FOXTAIL GREEN FOXTAIL COMMON RAGWEED
    GIANT FOXTAIL VELVETLEAF PIGWEED SPECIES
    GIANT RAGWEED SHEPHERD’S PURSE
    SMARTWEEDS PENNYCRESS
    COCKLEBUR LAMBSQUARTERS
    NIGHTSHADES WILD MUSTARD
    PERENNIAL WEEDS .
    CURLY DOCK CANADA THISTLE DANDELION
    HOARY ALYSSUM QUACKGRASS WHITE COCKLE
    YELLOW ROCKET
  • 30. Summary for establishment
    Weeds can be costly in establishment year
    Can reduce stand density
    Increase forage quantity (1st and maybe 2nd cutting)
    Weeds cause the increase
    Reduce forage quality (1st and maybe 2nd cutting)
    Depends on the weed species
    Management can reduce impact of weeds
    • Critical period 3-5 weeks after planting
    • 31. earlier if high weed density
    • 32. Gains in forage quality and stand establishment, not tonnage
  • Should I be concerned about weeds in late summer seedings?
    Volunteer wheat in
    alfalfa, a growing
    problem in Wisconsin
  • 33. Controlling volunteer wheat in summer seeding alfalfa
    alfalfa no-till drilled at 13 lbs/A
    8/18/2008
    8/15/2009
    Densities wheat
    12-49 plants /ft2
    7-94 plants /ft2
    Mid September
    Poast at 1.5 pt/A to ½ of the plots.
    Wheat: 6-8 inches tall
    Alfalfa
    4-6 trifoliate leaves
    4-5 inches tall
  • 34. Response of alfalfa density and yield from volunteer wheat 2008-09 = 12- 49 plants/ft22009-10 = 7-94 plants/ft2
    4-5 plants/ft2 is minimum threshold, but would like to have 30 plants/ft2
  • 35. Response of alfalfa density and yield from volunteer wheat
  • 36. Does volunteer wheat reduce establishment and yield?
    ESTABLISHMENT: Yes; 3 to 5 more plants/ft2 in untreated plots than treated.
    YIELD: Total yield is higher in untreated (42-69%), but % alfalfa can be reduced.
    FORAGE QUALITY: Untreated reduced quality needed for dairies.
  • 37. SUMMARY FOR NEW SEEDLINGS
    • Base weed management decisions on
    • 38. weed species and density
    • 39. soil moisture
    • 40. Need for high quality forage
    • 41. Many herbicide options available
    • 42. Scout carefully for
    weed species/density
    Alfalfa density/stand establishment
  • 43. WEED MANAGEMENT IN ESTABLISHED MIXTURES
    Different than seeding year as forages are well established and competitive
    Weed density typically low/absent
    Base management decisions on legume legume stand density and forage quality
    • Weeds fill in gaps created by thinning stands
  • Life History of Weeds of Concern in AlfalfaSurvey results from 285 PMU 2006
  • 44. Yellow Rocket and Forage Quality
    • Reduces protein content 2 to 3% compared to alfalfa
    • 45. Reduces digestibility and feed value
  • Dandelions and Protein Content
    • Reduce protein in first cutting only
    • 46. No effect on digestibility or consumption
  • Grass Protein Content
    Alfalfa =
    12-20%
  • 47. Treat or rotate crop?
    Treat if weedy but have:
    • > 4 to 5 plants/sq. ft
    • 48. >55 stems/sq. ft
    If below consider crop rotation
    Do spring and fall alfalfa counts
  • 49. What herbicide options do I have during establishment?
  • 50. Pursuit or Raptor
    • Broad spectrum of control by both foliar and root uptake (sprayed post; acts pre as well)
    • 51. Early postemergence application
    • 52. Alfalfa with it’s second trifoliate leaf or >
    • 53. Weeds 1 to 3 inches tall
    • 54. Raptor better on lambsquarters + foxtails
    • 55. Some injury can occur to alfalfa
    Can reach 20% yield reduction
  • 56. Roundup Ready alfalfa is now available!
    • Application timing: emergence - 5d before harvest
    • 57. Each application:
    • 58. no more than 1.5 lbsae/A
    • 59. Over the entire year:
    • 60. No more than 4.64 lbsae/A per year
    • 61. Applications must be at least 7 days apart
    • 62. glyphosate must be registered for use on RR alfalfa
  • Timing of application for pursuit/raptor vs glyphosate
    Few seedlings (< 10%) may not be Roundup resistant
    Recommend application at 3-4 trifoliate leaf to eliminate these seedlings (22 fl oz/A)
    Raptor/Pursuit
    Roundup
  • 63. Costs and benefits of Roundup Ready alfalfa
    Benefits:
    herbicide is cheap
    Roundup ($5-10) vs Pursuit/Raptor ($15-21)
    Application timing is flexible to crop, but 1 application needed
    Avoid potential yield loss from standard treatments
    Can apply to larger weeds and eliminate
    Control ALS resistant weeds
    Convenient
    Costs:
    Expensive
    $125/50 lbs bag technology fee
    Seed costs will be 2x nonproprietary varieties
    Will need to make a herbicide application
    No residual weed control
    May increase potential for glyphosate resistant weeds
    Future litigation and regulation?
  • 64. RR Alfalfa Yield Trials in WI
    • Seeding year 0.25-0.77 tons d.m./acre yield advantage (6-16%) for using glyphosate compared to raptor
    • 65. Subsequent total yield through the first three production years did not differ
    • 66. There were significant differences in yield among the RR varieties
  • Roundup Ready alfalfa
    What we don’t know
    • How well will it work in no-till where difficult to control perennial weeds are present?
    Dock species, Canada thistle, hoary alyssum, white cockle
    • Fit with alfalfa/grass mixtures
    • 67. Persistence in Wisconsin
    Data from Michigan suggests no increase in stand longevity
    Current research monitoring stand density of older fields
  • 68. RR Calculator
    • Excel spreadsheet that compares cost of RR vs. conventional alfalfa.
    • 69. Values are pre-entered that reflect Wisconsin’s the costs, use patterns, and yield.
    • 70. User can change data specific for a field or farm and provide a more accurate analysis of the costs. 
    http://www.uwex.edu/ces/forage/pubs/economics_RR_alfalfa.xls
  • 71. What ADDITIONAL herbicide options do I have in established crops?
    * For common crops (Corn, Soybeans, wheat)
  • 72. Summary
    • Weed management is dependent on several factors
    weed species, weed density, market for forage, growing conditions……….
    • Herbicides typically improve forage quality, but rarely improve yield
    Establishing alfalfa:
    Security against stand failure
    Weed free, high quality forage first cut
    Established alfalfa: Improved quality
    • Often weedy alfalfa fields are indications that the
    Crown density is below threshold rotated to another crop
  • 73. Questions?
    mrenz@wisc.edu