Field pea and lentil are poor competitors with weeds in the early-seedling stage. Weeds should be controlled by one to three weeks after crop emergence. Generally, apply broadleaf herbicides to small weeds for most effective control, and small pea and lentil plants to reduce risk of crop injury. Do not apply POST herbicides above 85 F or when the crops are under heat/drought stress.
Herbicides labeled for field pea and lentil:
Glyphosate (numerous trademarks) may be applied preplant (PP) or preemergence (PRE) as a burndown application. See label for rates and adjuvant use. Apply with ammonium sulfate fertilizer. Glyphosate is a nonselective, non-residual, translocated, foliar herbicide.
Far-Go at 1.25 pt/A preplant incorporated (PPI) for field pea and PPI or applied just after seeding with lentil for wild oat control.
Prowl/Pendimax at 1.2 to 3.6 pt/A applied in the spring controls annual grass and selected broadleaf weeds.
Trifluralin (several tradenames) at 1 to 2 pt/A or 5 to 10 lb 10G PPI is labeled for use in field pea for foxtail, barnyardgrass, and selected annual broadleaf weed control.
Treflan or Trilin 10G at 1 to 1.5 pt/A or 5 to 7.5 lb 10G/A PPI in the spring or 6 to 8.5 lb/A in the fall is labeled for use in lentil. Lentil tolerance to trifluralin is marginal. Cool soil conditions over an extended period of time will delay germination and emergence and increase risk of injury. Spring applications of Treflan/Trilin may cause a stand reduction compared to fall applications. If seeding into cool, dry soil after a spring application of Treflan/Trilin, the seeding rate should be increased by 15% to compensate for injury that may occur. Seeding no deeper than 1.5 inches will also reduce the potential for lentil injury.
Assure II at 8 to 10 fl oz/A plus oil adjuvant at 1% v/v controls annual grasses and quackgrass. Apply to both crops up to seed set.
Poast at 0.5 to 1.5 pt/A plus oil adjuvant at 1 pt/A controls annual grasses. Apply to lentil before bloom.
Sencor applied PRE at 0.33 to 0.5 lb 75DF/A or POST at 0.167 to 0.25 lb 75DF/A will suppress or control annual broadleaf weeds including common lambsquarters, mustard species, redroot pigweed, and smartweed. Thorough incorporation after PRE application by rainfall or mechanical methods is essential for weed suppression. Apply Sencor POST to weeds less than 2-inches tall and crop less than 6-inches tall. Crop injury possible if crop is stressed due to conditions including temperature extremes.
Roundup Ultra/RT or Roundup Original/RT at 0.5 to 2 pt/A may be applied as a harvest aid and desiccant when the legumes have 30% or less seed moisture. Allow a 7 day preharvest interval (PHI). Greater perennial weed control may be obtained by allowing a 10 to 14 day PHI. Do not apply to crop grown for seed.
Roundup Ultra/RT or Original/RT at 4 to 6 pt/A can be applied as a spot treatment for perennial weed control. Use a 2% solution. Apply to perennial weeds at or beyond the bud stage. Crop will be killed in treated areas.
Herbicides labeled only for field pea:
Dual II at 2 to 3 pt/A or Dual II Magnum at 1 to 2 pt/A PPI or PRE control foxtail, barnyardgrass and redroot pigweed.
Gramoxone Extra at 1.5 to 3 pt/A can be applied as PP or PRE burndown. A nonselective, non-residual, foliar herbicide. Apply with NIS.
Sonalan at 1.5 to 2 pt/A or 5.5 to 7.5 lb 10G/A PPI will control annual grasses and selected broadleaf weeds.
Basagran at 1 to 2 pt/A controls some annual broadleaf weeds and suppresses Canada thistle. Apply Basagran at 20 gpa and with oil additive at 1 to 2 pt/A. Apply two sequential applications 7 to 10 days apart each at 1 pt/A for less susceptible weeds like kochia or wild buckwheat and suppression of Canada thistle. Apply to pea with at least 3 pair of leaves or 4 nodes and no later than 30 days before harvest.
MCPA amine (certain tradenames) at 0.5 to 0.75 pt/A, Chiptox at 0.5 to 1.5 pt/A, or Thistrol at 2 to 6 pt/A will control many broadleaf weeds including wild mustard and redroot pigweed. Apply MCPA amine and Chiptox to 4- to 6-inch vines. Potential for crop injury exists and increases when peas are above 6 inches in height and when temperatures exceed 85 F or when the peas are under heat/drought stress. Apply Thistrol prior to flowering.
Pursuit at 2 fl oz/A or 0.72 oz WDG/A controls many broadleaf weeds and controls or suppresses foxtail and black nightshade. Apply with NIS at 0.25% v/v. Pursuit should be applied to peas at 2 to 3-inch height and prior to bloom. Pursuit will not control ALS- resistant kochia.
Herbicides labeled only for lentil:
Frontier at 20 to 32 fl oz/A can be applied PPI, PRE, or early postemergence for foxtail, barnyardgrass, nightshade and pigweed control.
Gramoxone Extra at 1 to 1.5 pt/A + NIS at 0.25% v/v can be applied as a nonselective preharvest desiccant. Apply when lentil is mature and at least 80% of the pods are yellow and no more than 30% of the leaves still green.
The majority of the above information was taken from the electronic version of the NDSU Extension Service circular W-253 ‘2000 Weed Control Guide’ (www.ext.nodak.edu/extpubs/plantsci/weeds/w253/w253w.htm). Consult the weed control guide and herbicide labels for additional details and required information regarding herbicide use.