Weed management in alfalfa. Mark Renz Agronomy Department University of Wisconsin-Madison

Transcription

1 Weed management in alfalfa Mark Renz Agronomy Department University of Wisconsin-Madison

2 Why manage weeds in alfalfa? 1. Risk of establishment failure 2. Reduce biomass of alfalfa 3. Reduce forage quality 4. Affect animal health

3 Establishment failure Possible, but uncommon in upper-midwest IF weed density is moderate to low AND soil moisture is adequate THEN successful establishment is likely Base decision on 1. weed species (perennial weeds worst) 2. weed density 3. soil moisture

4 Does risk vary with establishment method? Reduction in alfalfa plant density from weed competition study solo seeding companion crop Iowa 7-23% 61-70% Wisconsin 0-5% 26-31% Nebraska 28-31% Missouri 11-33% Michigan 10-15% 8-17% 5 state 16% Average 16% 35%

5 Effect of management method on stand density fall of seeding year study Gly vs UTC Gly vs Standard herbicide Wisconsin 0-5% less (NS) NS Nebraska 26% less NS Missouri 11-33% % less STD Michigan (NS) NS 5 state 13% less NS

6 Effect of management method on stand density fall of seeding year study Gly vs UTC Gly vs Standard herbicide Wisconsin NS NS Nebraska 26% less NS Missouri 11-33% % less STD Michigan NS NS 5 state 13% less NS

7 Effects of seeding rate when don t control weeds Study Missouri Alfalfa Density % reduction 5 lbs/a 43% 10 lbs/a 42% 15 lbs/a 28% 20 lbs/a 29%

8 Should I be concerned about weeds in late summer seedings? Volunteer wheat in alfalfa, a growing problem in Wisconsin

9 Response of alfalfa density and from volunteer wheat Variable UTC Poast UTC Poast Fall density (plants/ft2) Spring density (plants/ft2) Loss in density fallspring (plants/ft2) 10 (42%) 5 (21%) 2 (29%) - 1 (+2%) 4-5 plants/ft2 is minimum threshold, but would like to have 30 plants/ft2

10 Summary for risk of establishment failure Weeds can reduce stand density Watch out if: lower alfalfa densities (<10 lbs/a) High weed pressure Competitive weeds species in field Dry conditions that reduce alfalfa emergence Late summer seedings Well timed management can prevent establishment failure

11 Prevent yield loss Managing weeds will reduce forage yield Managing weeds increase yield of alfalfa When to manage How to minimize crop injury

12 When should we manage weeds to maximize Alfalfa yield? Depends on weed density and weed species Low to medium densities = 3-5 weeks after planting High densities =1-5 weeks after planting Herbicides differ in recommended time to apply

13 What herbicide options do I have during establishment? Herbicide Type Legume tol Grass control Broadleaf control Harvest restriction Eptam PPI F/G Y Y 14 days Treflan PPI G Y Y 21 days Butyrac Post G N Y 60 days Glyphosate* Post E Y Y 5 days Poast* Post E Y N 7-14 days Prowl Post 2TL, < 6 tall E Y Y day Pursuit* Post >2TL G Y Y 30 days Raptor* Post >2TL G Y Y 0 days Buctril* Post >4TL F/G N Y 30 days * Indicates most common herbicides used in WI

14 When can post herbicides be applied? Low-medium weed density Glyphosate:YYYYYYYYYYYYYYYYYYYYYYYYYYY Buctril :NNNNNNNNNNNNNNNNYYYYYYYYYY Butyrac :YYYYYYYYYYYYYYYYYYYYYYYYYYY Raptor :NNNNNNNNNNYYYYYYYYYYYYYYY Pursuit :NNNNNNNNNNYYYYYYYYYYYYYYY

15 When can post herbicides be applied? High weed density Glyphosate:YYYYYYYYYYYYYYYYYYYYYYYYYYY Buctril :NNNNNNNNNNNNNNNNYYYYYYYYYY Butyrac :YYYYYYYYYYYYYYYYYYYYYYYYYYY Raptor :NNNNNNNNNNYYYYYYYYYYYYYYY Pursuit :NNNNNNNNNNYYYYYYYYYYYYYYY

16 Response of alfalfa yield from volunteer wheat Variable UTC Poast UTC Poast Yield forage tons dm/a Yield alfalfa tons dm/a Forage quality (RFQ)

17 Herbicide injury to alfalfa Variable across herbicides, but only first cut Pursuit, Raptor, Buctril Applied before label recommends To stressed alfalfa Warm temperatures

18 Yield differences in establishment year 5 states including Wisconsin

19 Seeding year forage and alfalfa yield Michigan State University McCordick et al. 2008

20 Yield in Seeding Year of RR Alfalfa 2006 Table 3b Marshfield Lancaster Variety Glyphosate Conv Glyphosate Conv 425RR Tons/acre 4G18RR RR DK41-18RR Liberator RR WL 355 RR MEAN Difference Roundup Weathermax applied at 44 oz./ac at 4 th trifoliate Raptor and Poast Plus applied at 6 oz/ac and 24 oz/ac respectively at 4 th trifoliate Marshfield 2 cuts Lancaster 3 cuts

21 Yield loss from herbicide injury 5-20% yield reduction common in first cutting Raptor, Pursuit, Buctril Environmental conditions Stress to alfalfa Rarely do differences occur after first cutting in the seeding year No differences after seeding year unless establishment issues

22 Summary for reduction in alfalfa yield Manage weeds at the appropriate time to prevent alfalfa yield loss 1-5 weeks after emergence high weed density 3-5 weeks after emergence for low to medium weed density Differences exist in when you can apply POST herbicides Herbicide injury can occur Reduce yield 5-20% in first cutting Raptor, Pursuit, sometimes Buctril Rarely any additional yield loss in subsequent harvests

23 Is forage quality reduced by weeds? IT CAN BE Dependent on the weed species present, density, and stage of development Under certain situations some species can reduce feed quality below recommendations for dairies Usually differences seen in 1 st cut of seeding year Rarely does quality differ between herbicide treatments

24 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

25 Forage quality (RFV) changes from weed management Location 1 st cut 2 nd cut 3 rd cut % increase in RFV from herbicide treatment Wisconsin 37% 14% 2% Nebraska 14 to 19% 0 to 4% 0 to 7% Michigan 8 to 18% -8 to 0% -23 to 7% Average 19% 2% 0%

26 Weeds can reduce animal performance True, but few of these exist in alfalfa fields or are harvested before they mature and impact performance Poison hemlock Hoary alyssum

27 WEED MANAGEMENT IN ESTABLISHED STANDS Usually dominated by perennial weeds Many options present, but have poor performance on these species long plant-back intervals.

28 Yellow Rocket and Forage Quality Reduces protein content 2 to 3% compared to alfalfa Reduces digestibility and feed value

29 Dandelions and Protein Content Reduce protein in first cutting only No effect on digestibility or consumption

30 Grass Protein Content Grass Protein Content (%) Timothy 7.0 Tall Fescue 7.8 Quackgrass 9.2 Bromegrass 9.4 Alfalfa = 12-20% Orchardgrass 10.5 Reed Canary Grass 11.0 Average 9.2

31 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

32 What ADDITIONAL herbicide options do I have in established crops? Herbicide Type Legume tolerance Chateau Metribuzin Velpar PRE to weeds Pregreenup Pregreenup Grass contr. Brdlf contr. Harvest restriction Plant-back restriction* G/E Y Y 25 days 4 months F/G Y Y 28days 0-4 months G Y Y 30 days months Pursuit POST G Y Y 30 days months Raptor POST G Y Y 0 days months Glyphosate POST E Y Y 2-5 days 0 months * For common crops (Corn, Soybeans, Wheat)

33 Weed Management in Established Alfalfa Summary Weed management in established stands is much more difficult Perennial weeds Herbicides will improve alfalfa yield IF stand density is adequate Herbicides may improve forage quality Depends on weed species Often weedy alfalfa fields are indications that the Crown density is below threshold rotated to another crop

34 Summary Weed management is complicated in alfalfa Establishment Control weeds during first 3-5 weeks after emergence (1-5 high density/competitive weeds Ensure high quality alfalfa in first cutting with few to no weeds Rarely are large difference in yield seen after the first cutting Once established Manage weeds to maintain high yield and quality Typically management can help in years 3-4 IF stand density < threshold rotate

35 Roundup Ready alfalfa use recommendations Spray regardless of weed population Eliminate non-resistant seedlings (<10%) Application timing: emergence - 5d before harvest Applications must be at least 7 days apart Rate restrictions: Each application: no more than 1.5 lbs ae/a Over the entire year: no more than 4.64 lbs ae/a per year glyphosate must be registered for use on RR alfalfa

36 Benefits of Roundup Ready alfalfa 1. Herbicide is cheap compared to standards 2. Flexible application timing (crop and weed stage) 3. Avoid potential yield loss from standard treatments 4. Control ALS resistant weeds 5. Convenient 6. An option for perennial weeds in established stands that don t have long plant-back intervals

37 Costs of Roundup Ready alfalfa 1. Seed is more expensive 2. Recommend an application of glyphosate 3. No residual weed control 4. May increase potential for gly resistant weeds 5. Limited varieties available 6. Future litigation and regulation?

38 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.

39 Roundup Ready Alfalfa Removal 2,4-D + dicamba consistently provided >90% control of alfalfa across studies. Needed at least 1.0 lbs ai/a total ( usually 2pts/A ) Alfalfa was also effectively controlled with products that contained clopyralid (Stinger, Hornet) Addition of tillage improved control In corn, alfalfa control was improved by in season applications of systemic herbicides Dicamba: Distinct, Marksman Clopyralid: Stinger, Hornet

40 Roundup Ready Alfalfa removal Fall applications are more effective than spring Apply when temps get >50F to avoid reduced control While cover in spring may be low, plants may survive and be problematic later Scout the following spring in-crop (June) If volunteer alfalfa found applications of systemic herbicide should be planned Avoid relying on contact herbicides (Liberty, gramoxone) or pre herbicides (atrazine)

41 THANK YOU Questions?