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Weed management in alfalfa
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Weed management in alfalfa

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    Weed management in alfalfa Weed management in alfalfa Presentation Transcript

    • Weed management in alfalfa
      Mark J. Renz
      mrenz@wisc.edu
      University of Wisconsin-Madison
    • Costs of weeds in forages
      • Risk of establishment failure
      • Reduction in biomass of desirable plants (FEED)
      • Reduction in quality of feed
      • Affect animal health
      Poison
      Reduced feeding
    • 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
    • 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
    • Methods of establishing alfalfa
      • Direct seeding
      • Spring
      • Late summer
      • Seeding with a companion crop
    • Reduction in alfalfa plant density from weed competition
    • Reduction in alfalfa plant density from weed competition
    • 55 stems/square foot= 4-5 plants/square foot
    • Goal is for >30 plants/square foot by fall
    • Effects of seeding rate when don’t control weeds
    • 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
    • When should we manage weeds in Alfalfa?
    • Critical period Period of time after crop emergence that will not have yield reduction if weeds are removed
      % alfalfa yield (vs no weeds)
    • Critical period
      Note can change if more weeds!
      % alfalfa yield (vs no weeds)
    • Results
      • Critical period varied by location but ranged between 1st and 7thtrifoliate leaf
      • 3-5 weeks after planting
      • 1-5 weeks after planting
      • Same period was found for first harvest and first year yield of ALFALFA ONLY
      • Higher weed density caused critical period to begin earlier
    • What effect will weed management have on forage yield and quality?
    • Yield changes from weed removal
    • Yield changes from weed removal
    • Yield differences in establishment year5 states including Wisconsin
    • Forage quality (RFV) changes from weed management
      Can reduce RFV below recommendations for Dairies
      Depends on the weed species and weed density!
    • 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
    • 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
      • earlier if high weed density
      • 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
    • 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
    • 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
    • Response of alfalfa density and yield from volunteer wheat
    • 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.
    • SUMMARY FOR NEW SEEDLINGS
      • Base weed management decisions on
      • weed species and density
      • soil moisture
      • Need for high quality forage
      • Many herbicide options available
      • Scout carefully for
      weed species/density
      Alfalfa density/stand establishment
    • 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
    • Yellow Rocket and Forage Quality
      • Reduces protein content 2 to 3% compared to alfalfa
      • Reduces digestibility and feed value
    • Dandelions and Protein Content
      • Reduce protein in first cutting only
      • No effect on digestibility or consumption
    • Grass Protein Content
      Alfalfa =
      12-20%
    • Treat or rotate crop?
      Treat if weedy but have:
      • > 4 to 5 plants/sq. ft
      • >55 stems/sq. ft
      If below consider crop rotation
      Do spring and fall alfalfa counts
    • What herbicide options do I have during establishment?
    • Pursuit or Raptor
      • Broad spectrum of control by both foliar and root uptake (sprayed post; acts pre as well)
      • Early postemergence application
      • Alfalfa with it’s second trifoliate leaf or >
      • Weeds 1 to 3 inches tall
      • Raptor better on lambsquarters + foxtails
      • Some injury can occur to alfalfa
      Can reach 20% yield reduction
    • Roundup Ready alfalfa is now available!
      • Application timing: emergence - 5d before harvest
      • Each application:
      • no more than 1.5 lbsae/A
      • Over the entire year:
      • No more than 4.64 lbsae/A per year
      • Applications must be at least 7 days apart
      • 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
    • 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?
    • 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
      • Subsequent total yield through the first three production years did not differ
      • 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
      • Persistence in Wisconsin
      Data from Michigan suggests no increase in stand longevity
      Current research monitoring stand density of older fields
    • RR Calculator
      • Excel spreadsheet that compares cost of RR vs. conventional alfalfa.
      • Values are pre-entered that reflect Wisconsin’s the costs, use patterns, and yield.
      • 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
    • What ADDITIONAL herbicide options do I have in established crops?
      * For common crops (Corn, Soybeans, wheat)
    • 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
    • Questions?
      mrenz@wisc.edu