Bozeman, Montana, USA
April 12, 2010
By Fabian Menalled, MSU Extension Cropland Weed Specialist
As market demand rises for pulse crops, need increases to develop integrated management practices to prevent and control weeds. Weed control in lentils is particularly important, as this crop is a poor competitor due to its short height and slow early growth.
Lentil's low competitive ability is compounded when growing season temperatures are low or when moisture is scarce. In regions where lentils grow in less than optimal conditions, a weed management plan must consider the entire crop lifecycle including pre-sowing, emergence, vegetative, reproductive, and maturity.
Weeds compete with lentils for nutrients, moisture, space and yield. Moreover, weeds can harbor several insect pests and pathogens that may adversely affect the lentil crop. While crop reductions of up to 84 percent have been reported due to weed competition, the impact of weeds on lentils varies as a function of climate, weed density and length of competition period. For example, research conducted near Pullman, Wash., indicated that an infestation of three to seven wild oat plants per square foot for five weeks after lentil emergence did not reduce lentil yield. However, three wild oat plants per square foot reduced yield 32 percent if present for seven weeks, and 49 percent if present to harvest (11 weeks). At a density of seven plants per square foot, wild oat reduced lentil yield by 61 percent when competition lasted for 11 weeks.
In our region, important weeds invading lentil fields include catchweed bedstraw, Canada thistle, common lambsquarters, cow cockle, shepherds purse, henbit, Mayweed chamomile and dandelion. Of these, Canada thistle and catchweed bedstraw are particularly difficult to control and producers should sow lentils in fields free of these species.
To successfully manage weeds in lentils, producers should use a combination of cultural, physical, and chemical practices. Cultural practices to decrease weed pressure in lentil crops include prevention, seedbed preparation, variety selection, sowing and crop establishment, insect and disease management, nutrition management, and irrigation scheduling. Mechanical weed control practices represent a viable alternative for organic producers, but producers should minimize the risk of soil erosion due to excessive reliance on tillage. Also, mechanical weed control practices should be applied with caution due to the high sensitivity of lentil shoots and roots to damage.
In reduced-till or no-till lentil fields, herbicides are important tools to manage weeds. However, producers must be aware that herbicides are most effective when they are used as part of an integrated weed management program. Research has shown that the applicability and success of herbicide in lentil fields depends on the cropping system, land preparation methods, soil conditions, and weed problems. For example, Sencor (metribuzin) applied at recommended rates provides effective weed control, but it can cause crop damage in stressful conditions. Also, the high persistence sulfonylurea (SU) herbicides commonly used in small grain crops such as Ally (metsulfuron), Glean (chlorsulfuron), and Finesse (chlorsulfuron) can damage subsequent annual legumes, including lentils. Due to their persistence, it may be necessary to wait up to four years before seeding lentils, depending on the product, application rate, and weather conditions. A study conducted in Bozeman, Mont., showed that pea yields were reduced 16-19 percent 4.5 years after applying Finesse.
While information on commonly used herbicides used to manage weeds in lentils is provided below, producers should carefully read labels prior to using any herbicide. Additional information can be found at the 2009 South Dakota Weed Control in Pulse Crops (http://agbiopubs.sdstate.edu/articles/FS525PC.pdf) and the 2010 North Dakota Weed Control Guide (http://www.ndsu.edu/weeds/weed_control_guides).
Assure II (quizalofop): 5-12 ounces/Acre. POST. Annual and perennial grasses. Apply with crop oil concentrate (COC) or nonionic surfactant (NIS). Application intervals should be greater than seven days apart to allow re-growth. Do not apply within 60 days of harvest. Consult label for crop rotation restrictions.
Dual Magnum / generic S-metolachlor products: 1-2 pints/Acre. Preplant incorporated (PPI) or preemergence (PRE). For annual grass and some broadleaf weeds. Does not control emerged weeds. Incorporation improves control. Refer to label for specific rate information regarding soil texture and organic matter. Use low rates on coarse soils with less than three percent organic matter (OM) and higher rates on fine soils over three percent OM.
Far-Go (triallate): 1.5 quarts/Acre. PPI. Wild oat herbicide. Apply up to three weeks before seeding or after seeding before sprouts are .25 inch long. Apply prior to wild oat germination. A two-pass incorporation is recommended. Do not rotate to crops other than winter wheat, spring wheat and durum, triticale, barley, peas, lentils, and sugar beets for 12 months after a Far-Go application. In Montana, do not use Far-Go on fields to be seeded to hard red spring wheat with press drills if the field is or will be irrigated in the current growing season.
Outlook / generic dimethenamid-p: 10-16 ounces/Acre. Apply pre-plant surface or pre-emergence to lentils. Good to excellent control of several annual grasses. Fair to good control of certain annual broadleaves such as pigweed, waterhemp, or black nightshade. Adjust rate for soil type and OM. Consult your seed dealer for restrictions on specific varieties to avoid potential injury due to sensitivity. Emerged weeds are not controlled. May occasionally result in temporary spotting or browning of crop leaves. Lentils may be harvested 70 days after application. Refer to label for tank-mix options.
Paraquat products 0.8-1.3 pt paraquat 3L (.3-.48 lb active ingredient): Available in several brand name products including Gramoxone Inteon, Gramoxone Max, Firestorm, Parazone 3SL and others. Follow specific label directions for product used. HARVEST AID: Apply when at least 80 percent of pods are yellowing and mostly ripe. Follow handling precautions, as Paraquat is toxic when ingested. Restricted Use Pesticide.
Poast (sethoxydim): 2.5 pints/Acre, do not exceed 4.0 pints/Acre per season. POST: Annual grasses (2-4 inches). Requires COC additive. Apply to actively growing grasses. Do not graze or hay vines for livestock feed. Allow 50 days from application before harvest. Do not apply within 50 days of harvest.
Prowl, Prowl H2O, Pendimax, and other pendimethalin products (Formulation and use may vary. Follow directions for product used.): 1.5-3 pints/Acre Prowl H2O. PPI. Fall applications. Excellent control of several annual grasses and fair control of small-seeded annual broadleaves such as pigweed and lambsquarters. Poor or no mustard, nightshade, smartweed, or large-seeded annual broadleaves control. One inch rainfall or mechanical incorporation required prior to planting. Use lower rate on coarse soils and higher rate on fine-textured soils.
Roundup / generic glyphosate: Glyphosate is available in several products having different formulations and different amounts (pounds) of acid equivalent (ae) and active ingredient (ai). Consult labels for rates. BURNDOWN: Weeds should be actively growing. Avoid tillage for one day after treating annual weeds and three to seven days for perennials. Some products contain adequate surfactant; others require nonionic surfactants (NIS) and ammonium sulfate (AMS) additive. Use caution to avoid droplet drift to non-target crops. SPOT TREATMENT: Crop will be killed in treated areas. Allow a 14 day pre-harvest interval for spot treatment. Refer to specific glyphosate product label for rates, and precautions. PREHARVEST: Check label.
Treflan / generic trifluralin: Treflan HFP 1-2 pints/Acre (4 EC). PPI. Follow directions for product used as application rates and label instructions may differ. Tolerance is marginal and crop injury may occur. Rate should be adjusted depending on soil and rainfall or irrigation. Consult label for additional information. In Montana, uses of some Treflan formulations may be limited to those described in supplemental labeling.
Disclosure: Common chemical and trade names are used in this publication for clarity by the reader. Inclusion of a common chemical or trade name does not imply endorsement of that particular product or brand of herbicide and exclusion does not imply non-approval. Recommendations are not meant to replace those provided in the label. Consult the label prior to any application.
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