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
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
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.
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
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?