Weed Control in Green Peas Tim Miller WSU Mount Vernon NWREC

Positive Attributes of Green Peas Many herbicides available Densely-growing crop competes well with weeds Short-season crop Lower soil N may decrease weed growth

Preplant-incorporated Herbicides Available for Use in Green Peas Treflan (trifluralin) Far-Go (triallate) Buckle (trifluralin + triallate) Pursuit (imazethapyr) Prowl (pendimethalin) Sharpen (saflufenacil)

Preemergence Herbicides Available for Use in Green Peas Pursuit (imazethapyr) Prowl (pendimethalin) Dual Magnum (s-metolachlor) Command (clomazone) Sencor (metribuzin) Sharpen (saflufenacil)

Postemergence Herbicides Available for Use in Green Peas Pursuit (imazethapyr) Sencor (metribuzin) MCPA MCPB Basagran (bentazon) Poast (sethoxydim) Assure II (quizalofop)

Green Pea Studies Competitive Ability of Green Pea Reduced Rate Herbicide Trials Stale Seedbed Trials Spartan and Chateau Trials (if there is time…)

Pea Interference Study 'Charo' green pea Weeds removed from plots at weekly intervals and kept weed- free until harvest –1, 2, 3, 4, 5, and 6 weeks after emergence Weedy and weed-free plots

Pea Density and Pea Weight

Pod Production and Pea Yield

Pea Interference Studies Pea plant density slightly reduced by weed interference Pea size not reduced by duration of weed interference, but pod number decreased No yield loss if weeds were controlled by 5 weeks after emergence

Reduced Rate Herbicide Trials ‘ Snake ’ pea seeded early May PRE herbicides applied shortly after seeding POST herbicides applied late May to early June Weed control and crop injury estimated Peas and weeds harvested in late July/early August –Sampling within a 1 m 2 quadrat –Pea yield and plant biomass calculated –Weed biomass calculated –Seeds from weeds germinated in the greenhouse

Reduced Rate Herbicide Trials Tested herbicides were: –Command, PRE –Sencor, PRE and POST –Basagran, POST –MCPA, POST Various combinations of these products were tested at various rates

Reduced Rate Herbicide Trials Six “ full rate ” treatments: –Command (1.3 pt/a, PRE) –Sencor (5.3 oz/a, PRE) –Sencor (2.7 oz/a, POST) –MCPA (8 fl. oz/a, POST) –Basagran (1.5 pt/a, POST) –Command + Basagran (1.3 pt/a pt/a, PRE + POST)

Reduced Rate Herbicide Trials 14 “ partial rate ” treatments: –Command (11 fl. oz/a, PRE) –Sencor (2.7 oz/a, PRE) –Sencor (1.3 oz/a, POST) –MCPA (4 fl. oz/a, POST) –Basagran (12 fl. oz/a, POST)

Reduced Rate Herbicide Trials 14 “ partial rate ” treatments (cont.): –Command + Sencor 5.4 fl. oz/a oz/a, PRE –Command + Sencor 5.4 fl. oz/a oz/a, PRE + POST –Command + Basagran 5.4 fl. oz/a + 12 fl. oz/a, PRE + POST –Command + MCPA 5.4 fl. oz/a + 2 fl. oz/a, PRE + POST

Reduced Rate Herbicide Trials 14 “ partial rate ” treatments (cont.): –Sencor + Basagran 1.3 oz/a + 12 fl. oz/a, PRE + POST –Sencor + MCPA 1.3 oz/a + 2 fl. oz/a, PRE + POST –Sencor + Basagran 0.7 oz/a + 12 fl. oz/a, POST –Sencor + MCPA 0.7 oz/a + 2 fl. oz/a, POST –Basagran + MCPA 12 fl. oz/a + 2 fl. oz/a, POST

Pea Yield tons/a a a ab g

Biomass Returned to the Field tons/a abc ghi hij j ij ab abc a ab bcd g

Pea:Weed Biomass Ratios Divide the pea biomass by the weed biomass –If ratio is >1.0, more pea residue than weeds returned –If ratio is <1.0, more weeds than peas returned

Pea:Weed Biomass Ratio a b bc cd d d

Common Lambsquarters Germination Counts 2002 only weeds/m 2

Pineappleweed Germination Counts 2002 only weeds/m 2

Shepherd ’ s-purse Germination Counts 2002 only weeds/m 2

Reduced Rate Herbicide Trial—Total Weed Seed Germination Counts weeds/m 2

Reduced Rate Herbicide Trial—Total Weed Seed Germination Counts weeds/m 2

Reduced Rate Herbicide Trial—Total Weed Seed Germination Counts weeds/m 2

So in this case, return of weed seed to field would have resulted in: –Command + Basagran (PRE + POST) 3 weeds/m 2 (12,000/acre) –Sencor (PRE) 469 weeds/m 2 (1.9 million/acre) –Untreated check 8055 weeds/m 2 (32.6 million/acre) Weed Seed Germination

Reduced Rate Herbicide Trial Conclusions, All herbicide treatments resulted in at least 2 tons of harvested peas/a (6 full rates, 14 partial rates) –Based on dry biomass production, only 8 of 20 treatments adequately controlled weeds (4 full rates, 4 partial rates) –Weed dry biomass in the remaining 12 treatments exceeded pea dry biomass Even in a short-season crop like green peas, only 1 of 20 treatments prevented tremendous return of weed seed to the field (full rate of Command + Basagran)

Stale Seedbed Allow weed seeds to germinate, then kill them with herbicide or flame prior to crop emergence

Stale Seedbed Trial Overview Seedbed preparation: –Two weeks prior to seeding (14 d) –One week prior to seeding (7 d) –Three days prior to seeding (3 d) –Same day as seeding (0 d) Seeding dates ( ‘ Snake ’ ) –5/2507, 7/1/08, and 5/21/09

Stale Seedbed Trial Overview PREPO treatments (PRE to pea, POST to weeds): –Glyphosate (1 lb ae/a, 2 pt/a) –Paraquat (0.75 lb ai/a; 2.4 pt/a) –Glufosinate (0.5 lb ai/a; 4 pt/a) –Pyraflufen (0.004 lb ai/a; 2.5 fl.oz/a) –Flame (propane, open flame) –None

Stale Seedbed Trial Overview PRE treatments (residual herbicides applied at same time as the PREPO treatments): –Command (0.5 lb ai/a; 1.3 pt/a) –Prowl H2O (1.52 lb ai/a; 3.2 pt/a) –Sencor (0.38 lb ai/a; 8.1 oz/a) –None

Stale Seedbed Trial Overview Herbicide/flame application dates (days after seeding) –2007: 8 days –2008: 5 days –2009: 16 days Years were significantly different, so data are presented separately by year

Stale Seedbed Trial 2007 Results Weed control at 21 DAT generally good at all seedbed timings –Glyphosate, 93 to 95% –Paraquat, 94% –Glufosinate, 86 to 94% –Pyraflufen, 54% (14 d); 71 to 86% –Flame, 70% (14 d); 83 to 88% –None, 0% (14 d); 60 to 76% By harvest, weed control was poor to good

Weed Control At Pea Harvest July, 2007 % 80% 83% 78% 67%

Stale Seedbed Trial 2008 Results Green pea vine and pod fresh weight were not greatly affected by herbicide choice (ranged from 3.46 kg/m 2 for no herbicide to 3.90 kg/m 2 for glyphosate) Seedbed timing made no significant difference on green pea vine and pod fresh weight (3.54 to 3.79 kg/m 2 )

Weed Control At Pea Harvest September, 2008 % 86% 79% 83% 86%

Stale Seedbed Trial 2009 Results Peas in stale seedbeds prepared 14 days prior to seeding were injured up to 70% by initial POST herbicides and flame (shallower seeding in firm seedbeds?) –Pea vine and pod weight was reduced the most by glyphosate and paraquat Residual products provided 85 to 89% weed control, better than the 81% resulting when no residual product was used Green pea vine and pod fresh weight were not greatly affected by residual herbicide choice (about 2.8 kg/m 2 )

Weed Control At Pea Harvest July, 2009 % 94% 53%96%97%

Stale Seedbed Conclusions Weed control was generally good regardless of herbicide choice or flame –In 2007, flame and pyraflufen performed worse than other herbicides, particularly with 14 d seedbed –Ranged from 75 to 89% among all treatments in and from 80 to 99% in 2009 Injury was 70% for 14 d seedbeds in 2009, and was worse with glyphosate and paraquat on those seedbeds in 2009 Green pea did not respond greatly to seedbed timing any year –Weed control was slightly improved with 0 to 7 d seedbeds compared to 14 d seedbeds

Spartan and Chateau Trial 2003 Two newer soybean herbicides with good nightshade activity and were tested for selectivity in pea –Spartan (sulfentrazone, FMC) –Chateau (flumioxazin, Valent) Tests conducted in Mount Vernon, Paterson (Rick Boydston), and Pullman (Joe Yenish) on green peas, dry peas, lentils, and chickpeas

Spartan and Chateau Trial Mount Vernon trial, 2003 –‘ Snake ’ pea seeded May 6 –Herbicides applied alone and at 4 rates each June 4, as well as in mixture with Prowl or Dual Magnum at 2 rates each –Weed control and crop injury estimated –Peas and weeds harvested in late July Sampling within a 1-m 2 quadrat Pea yield calculated

Common Lambsquarters Counts Chateau weeds/m 2 Counted 14 days after treatment

weeds/m 2 Counted 14 days after treatment Common Lambsquarters Counts Spartan

Mount Vernon Results No significant difference in weed control No significant difference in pea injury No significant difference in pea yield

Spartan and Chateau Trial Paterson trial, 2003 –‘ Snake ’ pea seeded April 21 –Herbicides applied April 25 at same rates and combinations as at Mount Vernon –Weed control and crop injury estimated –Peas and weeds harvested in late July Sampling within a 1-m 2 quadrat Pea yield calculated

Pea Injury Chateau % Injury 35 days after treatment

Pea Yield Chateau tons/a

Pea Injury Spartan % Injury 35 days after treatment

Pea Yield Spartan tons/a

Spartan and Chateau Conclusions Injury from tank mixtures of Chateau or Spartan with Dual Magnum or Prowl was excessive at Paterson Weed control from combination treatments was superior to that from Chateau or Spartan alone The manufacturers have deemed green pea too sensitive to these products for registration, so further testing was dropped

Many Thanks! Funding for these studies provided by the –Northwest Ag Research Foundation –WA State Commission on Pesticide Registration –US Dry Pea and Lentil Council –Columbia Basin Vegetable Processors, –Pacific Northwest Vegetable Association Herbicides provided by the manufacturers Pea seed from National Frozen Foods Carl Libbey and the gang at WSU Mount Vernon NWREC