Managing Weeds and Insects in Alfalfa

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Managing Weeds and Insects in Alfalfa

• Richard N. Arnold
• College Assistant Professor
• NMSU Ag Science Center

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Alfalfa History

• The name alfalfa comes from the Arabic language,
  meaning best fodder
• Most authorities believe that alfalfa originated
  in southwestern Asia
• First attempt to grow alfalfa in the U. S. was in
  Georgia in 1736
• Introductions into California from Peru in 1841

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Alfalfa Production

• Harvested acreage in U.S. in 2001 was
  approximately over 23 million acres
• Average Yield was approximately 3.4 t/A at an
  estimated value of 102.50/t
• Harvested acreage in San Luis Valley in 2001 was
  approximately 167,000 (Merlin Dillon)
• Average yield was approximately over 5.5 t/A
  (Merlin Dillon)

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Alfalfa Production Cont.

• The yield record for one acre of alfalfa is 10
  t/A without irrigation
• The yield record for one acre of alfalfa is 22
  t/A with irrigation

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Herbicide Findings

• In the National Center for Food Agricultural
  Policy of a 40 crop summary found that
  approximately 200 chemicals are used in the U.S.
• An average cropland acre is treated with two lbs
  of herbicide active ingredient costing
  approximately 30.00/A

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Herbicide Findings Cont.

• If U.S. farmers employed an additional 7 million
  weeders and increased cultivation, overall crop
  production would decline by approximately 21
  percent
• The average wage rate for farm workers was
  approximately 10/A in 1940s and now labor cost
  would be approximately 700/A (herbicides 30 to
  50/A)

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Herbicide Findings Cont.

• Herbicides has helped growers reduce tillage for
  weed control (less erosion)
• Without no-till farming for crop production,this
  could result in an increase of approximately 304
  billion pounds of soil erosion (approx. 76,000
  acres)

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Alfalfa Insects
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Vertebrate Pests

• Pocket Gophers are burrowing rodents, so named
  because they have fur-lined pouches outside of
  the mouth, one on each side of the face
• Medium sized 5 to 14 in long
• Fur fine and soft and vary in color from pale
  brown to black or white (gray)
• Spend most of their time underground, rarely seen
  on surface

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Pocket Gopher Cont.

• Have a wide habitat (sea level to 12,000 ft)
• Tunnel the soil and make mounds
• Eat underground plant structures
• Cause mounds of soil in alfalfa fields (fields
  uneven)
• A single burrow system may contain 200 yards of
  tunnels
• May make 1 to 3 mounds per day

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Pocket Gopher cont.

• A healthy stand of alfalfa can tolerate some
  gopher feeding, large populations cause serious
  damage
• Damage more prevalent in sprinkler irrigated
  fields than flood
• Methods of control include traps, baits,
  fumigating, flooding

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Pocket gopher
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Pocket gopher mound
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Insects

• A good field monitoring program is essential for
  good IPM strategies
• Use a good sampling method to estimate insect
  population
• Check each field at least once per week
• Also, the importance of correctly identifying
  pests and damage symptoms cannot be overemphasized

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Insects Cont.

• Monitoring methods include Sweep net, vacuum
  collector, visual counts, and monitoring of
  natural enemies
• When localized high densities of pests occur in
  parts of the field, monitor these trouble spots
  regularly until the problem disappears or
  treatments are required

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Alfalfa Weevil

• Weevils cause two kinds of damage, defoliation
  and damage to regrowth buds, which stunts growth
  and sometimes kills stems
• Studies in Artesia show losses from ½ to ¾ tons/A

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Alfalfa Weevil Cont.

• When weevil larvae average 3 or more per square
  foot, or 8 to 10 per sweep net, or when alfalfa
  shows excessive damage control measures are
  necessary (swath or treat)
• Look for shot-holes in the stems of alfalfa

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Alfalfa Weevil Cont.

• Is a serious pest and is found throughout NM
  wherever alfalfa is grown
• Adult weevils feed on foliage and lay eggs in the
  stems throughout the winter months
• When weather warms in spring (March-April) the
  eggs hatch and the larvae begin to feed
• Larvae is tiny and is yellowish-green
• Adults is light brown with gray marking down backs

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Alfalfa Weevil Cont.

• Because of the relatively short residual of the
  some recommended insecticides, and heavy
  infestation levels more than one application may
  be necessary
• In San Juan County usually late April to mid May
  weevils show up, (to late to spray) but are
  sporadic from year to year and usually cutting
  the crop early rids the alfalfa of the pest

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Alfalfa Weevil Cont.

• Baythroid 2, 0.8-2.8 fl oz/A, Days to harvest 7,
  REI 12 hr
• Guthion Solupak, (50 WSP), ½-1.0 lb/A, Days to
  harvest 14-21, REI 48 hr
• Furadan 4F, ½-2 pts/A, Days to harvest 7 to 28,
  depending on rate, REI 48 hrs
• Ambush 2 EC, 3.2-12.8 fl oz/A, Days to harvest 0
  to 14, depending on rate, REI 24 hrs
• Pounce 3.2 EC, 2-8 fl oz/A, Days to harvest 0 to
  14, depending on rate, REI 24 hrs

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Weevil adult
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Weevil larvae
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Weevil eggs
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Aphids (Pea and Blue)

• The two species, which are similar in appearance
  and often occur together in the same field (can
  be confused with one another)
• The best way to distinguish the two aphids is to
  examine the antennae with a hand lens
• Pea aphid antennae is green with a narrow dark
  band at end of each segment
• Blue aphid antennae is uniformly dark

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Pea and Blue Aphid Cont.

• Pea aphid is tolerant to higher temperatures
• Blue aphid usually appears first (do to
  temperature)
• When pea aphid counts average 10 to 15 per stem
  or 150 per plant control measures are needed
• When Blue aphid counts average 10 to 12 per stem
  on new growth in spring control measures are
  needed

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Pea and Blue Aphid Cont.

• Blue aphid stunts growth early in season, plants
  have smaller leaves, shorter internodes, leaf
  curling, yellowing and leaf drop, plants exhibit
  large amounts of honeydew
• Pea aphid causes the same symptoms but in larger
  numbers
• Important to control in alfalfa grown for seed

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Pea and Blue Aphid Cont.

• Plant resistant varieties
• Predators, parasites, and fungi play a major role
  in control (maintain natural enemies)
• Lorsban 4E, 0.5-2 pts/A, Days to harvest 7, 14,
  and 21 (depends on rate), REI 24hr
• Lannate LV, 0.75-3 pts/A, Days to harvest 7, REI
  48 hr
• Malathion 8EC, 0.8-1.0 pt/A, Days to harvest 0,
  REI 12 hr

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Pea and Blue Aphid Cont.

• Ambush 2EC, 3.2-12.8 fl oz/A, Days to harvest
  0-14 (depending on rate), REI 24 hr
• Pounce 3.2EC, 2-8 fl oz/A, Days to harvest 0-14
  (depending on rate), REI 24 hr
• Dimethoate 4E, 0.5-1.0 pt/A, Days to harvest 10,
  REI 48 hr

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Pea aphid
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Pea aphid antennae
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Blue aphid
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Spotted Alfalfa Aphid

• The spotted alfalfa aphid is pale yellow with
  four to six rows of dark spots, each with a spine
  running lengthwise down its back (easy to
  distinguish from pea and blue aphid)
• Feeds on lower portions of plant and on
  undersides of leaves
• Also secretes large amounts of honeydew
• Very tolerant to heat (above 80 degrees)

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Spotted Alfalfa Aphid Cont.

• This aphid injects a toxin into alfalfa which
  causes yellowing and severe stunting of growth
• Plants can be killed when infestations are heavy
  and fungus may develop on the honeydew
• This causes a reduction in palatability and
  quality

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Spotted Alfalfa Aphid Cont.

• Can reproduce year round
• As many as 20 generations can be produced each
  year
• Winged females may fly more than 70 miles with
  the aid of winds (some farther with are winds)
• Each one is a female (high biotic potential)

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Spotted Alfalfa Aphid Cont.

• Plant resistant varieties
• Promote natural enemies (lacewing, lady bird
  beetles, and parasitic wasps)
• Lorsban 4E, 0.5-2.0 pts/A, Days to harvest 7, 14
  and 21, (depends on rate), REI 24 hr
• Malathion 57EC, 1.5-2.0 pt/a, Days to harvest 0,
  REI 12 hr
• Ambush 2EC, 3.2-12.8 fl oz/A, Days to harvest
  0-14 (depends on rate), REI 24 hr
• Pounce 3.2EC, 2-8 fl oz/A, Days to harvest 0-14
  (depends on rate), REI 24 hr

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Spotted alfalfa aphid
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Armyworms

• Two types beet and western yellowstripe
• Beet armyworm, is usually light olive green, but
  may range in color from purplish green to almost
  black
• Western yellowstriped armyworm is usually black
  with two prominent orange yellow stripes and many
  narrow stripes down each side

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Armyworms Cont.

• They skeletonize foliage, leaving the veins of
  leaves intact
• In San Juan County they can be a serious problem
  (mainly western yellowstriped) after the first
  cutting or in fall-seeded stands
• Treat when there is an average of 2 to 3 (or
  more) larvae per square yard

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Armyworms Cont.

• Lorsban 4E, 0.5-2.0 pts/A, Days to harvest 7, 14
  and 21 (depending on rate), REI 24 hr
• Lannate LV, 0.75-3.0 pts/A, Days to harvest 7,
  REI 48 hr
• Ambush 2EC, 3.2-12.8 fl oz/A, Days to harvest
  0-14 (depending on rate), REI 24 hr
• Pounce 3.2EC, 2-8 fl oz/A, Days to harvest 0-14
  (depending on rate), REI 24 hr

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Armyworm
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Army Cutworms

• When full grown, army cutworms are about one and
  a half in long, grayish with splotches of white
• Has alternating dark and whitish stripes on the
  upper body surface
• Dingy is grayish-brown has darker v shaped
  pattern on back resembling a tractor tract

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Army Cutworm Cont.

• Cutworms feed on newly emerging leaves near the
  crown
• During daylight they are often found in loose
  soil surrounding the plant
• Economic threshold is four or more army cutworms
  ft2 on established stands, but just two in fields
  seeded last year

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Army Cutworm Cont.

• Lorsban 4E, 0.5 to 2 pts/A, Days to harvest7, 14,
  21, (depending on rate), REI 24 hr
• Baythroid 2, 0.8 to 2.8 fl oz/A, Days to harvest
  7, REI 12 hr
• Ambush 2E, 3.2 to 12.8 fl oz/A, Days to harvest
  0-14, REI, 24 hr
• Pounce 3.2EC, 2-8 fl oz/A, Days to harvest 0-14,
  REI, 24hr

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Dingy cutworm
Army cutworm in alfalfa field in southern
Colorado 2-03
Army cutworms
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False cinch bug Cont.

• Adults grayish-brown, narrow-bodied, and about
  1/8 in long.
• Egg laying occurs in late winter or early spring,
  and they hatch in 4-7 days
• Active from about the middle of May to late
  September

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False cinch bug Cont.

• They have piercing-sucking mouthparts and feed by
  removing fluids from their host plants
• Plants generally wilt, leaves turn brown and die
• They prefer weeds in the mustard family and they
  can concentrate in large numbers under windrows
  or bales of alfalfa

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False cinch bug Cont.

• Methyl Parathion 4EC, 1.5 pts/A, Days to
  harvest15, REI 72 hr (grass hay)

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Other Insects that Attack Alfalfa

• Cutworms
• Webworms
• Sowbugs
• Leafhoppers
• Lygus Bus
• Thrips
• Spider Mites
• Clover Mites
• Grasshoppers

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Lygus
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Grasshoppers
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Mites
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Blister beetles
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Beneficial Insects of Alfalfa

• Lady beetle adult and larvae
• Bigeyed bugs
• Damsel bugs
• Lacewings
• Parasitic wasps
• Assassin bug

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Lady beetle
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Lady beetle larvae
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Big-eyed bug
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Damsel bug
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Damsel bug larvae
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Lacewing
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Parasitic wasp
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Assassin bug
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Weed Identification

• Weed problems in alfalfa can be subdivided into
  three different groups with a mixture of weed
  species involved in each
• Stand establishment weeds
• Cool season weeds (winter annuals)
• Summer weeds

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Weed ID Cont.

• Weeds do not kill alfalfa plants directly
• They reduce production by competing with alfalfa
  for nutrients, water and light
• They lower quality by reducing feed value
• Weeds can contribute to stand loss at any time in
  the life of an alfalfa field, but are especially
  detrimental during new stand establishment

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Weed ID Cont.

• In established stands in San Juan County weeds
  like downy brome, flixweed, shepherdspurse,
  foxtail barley, and dandelion cause yield and
  quality losses
• When stands begin to thin many annuals like
  Russian thistle, pigweeds, foxtails (green and
  yellow) lambsquarters, barnyardgrass, and kochia
  can be problems during the summer months

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Weed ID Cont.

• Downy brome is a winter annual grass 4 to 30 in
  tall, reproducing by seed
• Leaf sheaths and flat blades are densely covered
  with soft hair
• Awns are 3/8 to 5/8 in long, usually purplish in
  color when mature

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Downy brome
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Weed ID Cont.

• Flixweed is a winter annual 8 to 24 in tall
• Petals small yellow or greenish-yellow
• Seed pod partitioned with 2 to 3 longitudinal
  nerves

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Flixweed
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Weed ID Cont.

• Shepherdspurse is a winter annual 3 to 18 in tall
  with stems erect, slender, one to several from a
  basal rosette
• Leaves alternate with lower ones usually deeply
  lobed, upper ones are few
• Seed pod more or less heart shaped, and two
  celled

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Shepherdspurse
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Weed ID Cont.

• Foxtail barley is a perennial that reproduces by
  seed
• Grows 1 to 2 ft tall and produces a pale green
  bushy type spike
• Awns are 1 to 2 ½ in long

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Foxtail barley
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Weed ID Cont.

• Dandelion is a short lived perennial with milky
  juice from an often branched taproot
• Reproduces by seeds and shoots from root crowns
• Leaves clustered at the top of the root crown
• Vary in size from 2 to 12 in long
• Produces a yellow petal like ray flower

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Dandelion
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Herbicides for Seedling Alfalfa

• Balan DF, 2-2.5 lb/A, Preplant Incorporate (PPI)
  before seeding, pigweeds, carelessweed,
  lambsquarters, barnyardgrass, foxtails and
  sandbur
• Buctril 4EC, 0.5-0.75 pt/A, Postemergence (POST),
  alfalfa minimum of 2 to 4 trifoliolate leaves,
  broadleaf weeds only

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Herbicides for Seedling Alfalfa Cont.

• Butyrac 200, 2-6 pts/A, POST, alfalfa a minimum
  of 2 to 4 trifoliolate leaves, temperature
  dependant, broadleaf weeds only
• Eptam 7E, 3.5 pt/A, PPI immediately, has
  chemigation label, nightshades, pigweeds,
  lambsquarters, barnyardgrass, foxtails, and
  sandbur

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Herbicides for Seedling Alfalfa Cont.

• Pursuit Eco-Pak, 1.08-2.16 oz DG/A, POST, alfalfa
  a minimum 2 trifoliolate leaves, mustards,
  nightshades, cocklebur, pigweeds, kochia,
  barnyardgrass, foxtails, crabgrass
• Select, 6 oz/A, POST, alfalfa a minimum of 2
  trifoliolate leaves, must have an additive added,
  only grasses
• Raptor, 4 to 6 fl oz/A, POST, alfalfa a minimum 2
  trifoliolate leaves, same broadleaf weeds as
  Pursuit, but somewhat better grass control (downy
  brome)

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Rotation

• Raptor- Region 1, clearfield wheat and canola
  anytime, alfalfa, wheat- 3 months, Barley
  depending on pH and rainfall 9 to 18 months
• Pursuit-alfalfa, Rye, Wheat, Dry Beans-4 months,
  Barley 9 months, lettuce 18 months

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NMSU Alfalfa Seedling Trials
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Raptor 0.032 lb ai/A
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Raptor 0.04 lb ai/A
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Pursuit 0.063 lb ai/A
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Raptor Select 0.032 0.094 lb ai/A
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Raptor Buctril 0.032 0.25 lb ai/A
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Check
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Herbicides for Established Alfalfa

• Karmex DF, 2-3 lb/A, apply before alfalfa breaks
  dormancy, foxtails, Russian thistle,
  lambsquarters, pigweeds, mustards, downy brome
• Zorial Rapid 80 DF, 1.25-2.5 lb/A, apply before
  alfalfa breaks dormancy, downy brome,
  barnyardgrass, pigweeds, kochia, and prickly sida

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Herbicides for Established Alfalfa Cont.

• Sencor DF, 0.33-1.3 lb/A, apply before alfalfa
  breaks dormancy, mustards, flixweed, kochia,
  pigweeds, downy brome, foxtail barley, wild oat
• Poast Plus 1EC, 0.75-3.75 pts/A, can be applied
  anytime to alfalfa, weed heights depend on
  control, must have a additive added, controls
  only grasses
• Select, 8 oz/A, weed heights depend on control
  must have additive added, only grasses

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Herbicides for Established Alfalfa Cont.

• Sinbar WP, 0.5-1.5 lb/A, do not use over 1.0 lb/A
  in San Juan County, apply before alfalfa breaks
  dormancy, mustards, lambsquarters, downy brome
  cheatgrass, foxtails
• Velpar L, 1 qt/A, apply before alfalfa breaks
  dormancy, mustards, filaree, chickweed, downy
  brome, cheatgrass

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NMSU Established Alfalfa Trials
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Karmex 2.0
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Karmex 3.0
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Sencor 0.32
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Sencor 0.5
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Velpar 0.25
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Velpar 0.5
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Sinbar 0.75
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Check
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Rotation

• Karmex- 2-years,
• Zorial Rapid 80- 16 months
• Sencor- alfalfa, potato, 4 months, barley, wheat,
  8 months
• Velpar-do not plant any crop except corn, root
  crops within 2 years after treatment. Potato and
  carrot 12 months unless rate exceeded 2 pts/A.

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Herbicide Costs

• Pursuit EcoPak 11.78/oz
• Butyrac 200 45.85/gal
• Buctril 64.74/gal
• Select 208.61/gal
• Poast 76.75/gal
• Velpar L 66.27/gal
• Karmex DF 5.09/lb
• Sencor 4F 111.88/gal
• Eptam 7E 36.26/gal
• Raptor 593.00/gal

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Thank You

• Always remember to read the pesticide label
  before use
• Contact your local County Extension Agent for any
  questions