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United States Department of Agriculture

Agricultural Research Service

Morton Weed Control
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Controlling Weeds in Fall Seeded Lentils
Joe Yenish, Extension Weed Scientist
Washington State University

Weed control in fall seeded (winter) lentils present challenges and opportunities to growers. Since winter lentils are only now becoming available, little information on weed control and crop injury is available.

It is important to combine pre- and postemergence herbicides when planning weed control in fall seeded lentils. Pursuit when used in combination with Prowl or other herbicides should be effective in controlling or suppressing many annual broadleaf and grass weeds. Grass weeds that may escape or emerge in the spring of the year can be controlled with Assure II or Poast.

Weed species which expected to become a big problem in fall seeded lentils include prickly (china) lettuce and mayweed chamomile (dogfennel). Metribuzin (Sencor) has proven to be the lentil herbicide most effective for control of these two weeds. Sencor is also the only broadleaf herbicide labeled for postemergence applications in lentils and is also labeled for preemergence applications. Preemergence use of Sencor is limited to a single application of 1/4 to 1/2 lbs. Sencor/acre which will control or suppress fall emerging prickly lettuce and other weeds. When using Sencor preemergence, lentils must be planted no less than 2" deep and should not be used on fields with sandy soils or soils with less than 1.5% organic matter to lessen crop injury concerns. Applications should also be avoided on clay knobs or other areas with poorly covered subsoils. Heavy rains following Sencor applications may also increase crop injury.

Growers should also expect to make a second application of Sencor at 1/6 to 1/3 lbs/acre in the spring of the year to control or suppress spring emerging prickly lettuce or mayweed chamomile. Likely, lentils will become chlorotic (yellow) following a postemergence application of Sencor. Applications should be avoided following 3 days of cool, wet, overcast conditions or when these conditions are expected immediately after a Sencor application. Sencor should not be applied to wet foliage.

Pre- and postemergence applications of Sencor must not exceed a total of 2/3 lbs/acre per crop. Growers may want to assume a 1/3 lbs Sencor/acre postemergence application and adjust preemergence applications accordingly.

Research will be conducted at WSU this fall and spring to determine the best way to utilize pre- and postemergence applications of Sencor. Also, research is being conducted to discover and label additional products for use in lentils. Growers could expect to see 2,4-DB (Butyrac 200) labeled within the next few years.

REMEMBER TO READ AND FOLLOW ALL LABEL DIRECTIONS

LENTILS-Wild Oats
Preplant or preemergence
  • triallate
    Far-Go

Rate 1.25 Ib ai/A
Time Apply pre- or postplant; incorporate thoroughly 1 to 2 inches deep.
Remarks Do not graze treated areas.

 

LENTILS -Annual Grass and Broadleaf Weeds

Preplant incorporated
  • trifluralin
    Trilin
Rate 0.5 to 0.875 lbs ai/A
Time Apply preplant and incorporate. May be fall applied.
Remarks Incorporate thoroughly 1 to 2 inches deep immediately after appying. Use lower rate on coarse soil. Caution May injure stressed crop seedlings.
Preplant incorporated or preemergence
  • metolachlor
    Dual Magnum
Rate 1 to 3 lb ai/A
Time Apply preplant incorporated or preemergence.
Remarks Application rate depends on soil type and organic-matter content.
Caution Do not cut for hay within 120 days after application.
Preplant, preemergence, or early postemergence
  • dimethenamid Frontier or
  • dimethenamid-P Outlook
Rate Frontier: 0.76 to 1.46 lb ai/A (16 to 32 oz/A). Outlook: 0.56 to .98 (12 to 21oz/A).
Time Apply preplant, preemergence, or early postemergence.
Remarks Consult label for application rate in relation to soil type. Use lower rate on coarse soils with low organic matter or low cation exchange capacity (CEC). Control is best if incorporated into soil by overhead moisture or a light tillage (1 to 2 inches deep) before weed seedlings emerge.
Caution Do not apply through any type of irrigation system. To avoid injuring sensitive varieties, before applying Frontier consult your local seed company supplier about your variety's sensitivity.

 

LENTILS-Annual Grasses

Preplant
  • pendimethalin Prowl (3.3 EC)
Rate 0.5 to 1.5 lb ai/A (1.2 to 3.6 pints/A Prowl). Use lower rate on coarse soils, higher rate on fine soils.
Time Apply up to 60 days preplant and incorporate by following label instructions.
Remarks Incorporate thoroughly to a depth of 1 to 2 inches. Apply in a minimum of 10 gal/A water or in 20 or more gal/A liquid fertilizer. Also controls several broadleaf weed species.
Caution Do not apply to pea or lentil forage, silage, hay, or straw grown for feed.
Postemergence
  • sethoxydim Poast
Rate 0.28 to 0.34 Ib ai/A (1.5 to 1.8 pints/A Poast)
Time Apply to wild oats and volunteer cereals up to 4 inches tall and to other grasses according to the label.
Remarks Refer to label for specific herbicide rates, weed species, and weed size. Always add a nonphytotoxic oil concentrate at 2 pints/A.
Caution Control is erratic on grasses stressed by drought, temperature extremes, herbicide injury, etc. Do not apply if rain is expected within 1 hour of application. Do not apply within 50 days of harvest. Do not mix with other pesticides. Do not apply more than 0.75 Ib ai/A in one season.
  • quizalofop P-ethyl Assure II
Rate 0.04 to 0.08 lb ai/A (6 to 12 fl oz/A Assure II)
Time Postemergence to grasses. See label for details.
Remarks Controls both annual and perennial grasses. Always use either a nonionic surfactant at 1 quart/100 gal or a petroleum-based crop oil at 1 gal/100 gal.
Caution Do not apply more than 14 fl oz/A per season. Preharvest interval is 60 days. Do not feed vines or hay.

LENTILS-Annual Broadleaf Weeds
Preplant
  • pendimethalin Prowl
Rate 0.5 to 1.5 lb ai/A (1.2 to 3.6 pints/A Prowl)
Time Apply preplant and incorporate.
Remarks Incorporate thoroughly 1 to 2 inches deep after appying. Use lower rate on coarse soil.
Caution Do not apply to pea or lentil forage, silage, hay, or straw grown for feed.
Preemergence
  • metribuzin Lexone or Sencor
Rate 0.25 to 0.38 Ib ai/A (5.3 to 8 oz/A of the 75% DF)
Time Apply after seeding but before lentils germinate. Metribuzin may be incorporated 1 to 2 inches deep if soil is dry. If moisture is present or expected, preemergence treatment is best. Do not apply within 75 days of harvest.
Remarks Will not control nightshade.
Caution Determine your lentil variety's tolerance before applying metribuzin. See other label precautions. Do not use on coarse soils or on any soil with less than 1.5% organic matter. Do not use on clay knobs or poorly covered subsoils. Crop may be injured if it becomes stressed. Follow label regarding crop rotations. Do not apply more than once per season. Do not apply on seedings less than 2 inches deep.
  • imazethapyr Pursuit
Rate 0.047 Ib ai/A (3 oz/A Pursuit, 1.08 oz/A of the 70% DC)
Time Apply after planting but before crop emerges, or preemergence followed by shallow incorporation. Incorporation improves control. Remarks Registered for use only in certain counties in Oregon, Washington, and Idaho; see current label for appropriate use areas. May be tank-mixed with metribuzin to help control lambs-quarters or mayweed chamomile. Rain required to move surface applications into weed germination zone. If adequate moisture is not received within 7 days of application, control escaped weeds with rotary hoeing or cultivation.
Caution Wheat and barley may be planted 4 months after last application. Do not feed treated lentil hay or straw to livestock.
Postemergence
  • metribuzin Lexone or Sencor
Rate 0.15 to 0.25 Ib/A (3 to 5.3 oz/A of the 75% DF)
Time Apply to weeds less than 2 inches high and before lentils are 6 inches high.
Remarks Will not control nightshade.
Caution Do not use on coarse soils or on soils with less than 1.5% organic matter. Do not use on clay knobs or poorly covered subsoils. Crop symptoms may appear especially under moist conditions. Use the low rate when conditions are moist . Do not apply within 75 days of harvest. Do not apply more than once preemergence and once postemergence per season. Do not apply over moist soils, wet foliage, or within 3 days of cool, wet weather.

Mayweed Chamomile and Prickly Lettuce Photos by
Dean Swan


Last Modified: 7/16/2004
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