Sugar beet-Armyworm

Beet armyworm (Spodoptera exigua)

Bertha armyworm (Mamestra configurata)

Western yellowstriped armyworm (Spodoptera praefica)

Pest description and crop damage Armyworms occasionally are severe defoliators, especially in western Idaho. Damage appears as skeletonized leaves with only leaf veins and petioles remaining. Armyworms are related closely to cutworms but generally are slightly larger, more brightly colored, and actively feed on plants during the day. When infestations become dense and crowded, larvae migrate together from field to field; sugar beets adjoining infested alfalfa hay fields or cereals may be completely defoliated by migrating armyworms.

Beet armyworms are dull green caterpillars with a dark, broad stripe along each side and many smaller, light wavy lines down the back. They are about 1.25 inches long when mature.

Bertha armyworms are highly variable, from light yellow-green to gray-black, with a yellow-orange stripe along the side that divides the caterpillar body into a dark upper half and a pale bottom half. They are about 1.25 inches long when mature.

Western yellowstriped armyworms have wide, velvety black stripes along the back with many narrower, bright yellow stripes along the sides. They are about 1.5 inches long when mature.

Scouting and thresholds No formal economic thresholds exist for armyworm insecticide treatment decisions in sugar beets. Consider insecticide application if field scouting shows that infestations average one armyworm larva per plant early in the season. Older plants can tolerate considerable defoliation without any economic loss of root yield or sucrose content.

Management-biological control

Armyworms commonly are attacked by parasitic wasps and flies that can help keep infestations in check. We do not yet know enough about arthropod natural enemies to suggest practical ways of manipulating and enhancing their effects other than avoiding any unnecessary insecticide applications.

  • Bacillus thuringiensis aizawai (Agree WG, XenTari - live spores of an insect-killing bacterium)-See label for rates. PHI 0 days. Biological insecticide most effective against small, newly hatched larvae. No contact action; larvae must eat treated leaves. Use a spreader-sticker. REI 4 hr. Some formulations are OMRI-listed for organic use.
  • Bacillus thuringiensis kurstaki (Biobit HP, Crymax, Deliver, Dipel DF, Javelin WG, and others - live spores of an insect-killing bacterium)-See label for rates. PHI 0 days. REI 4 hr. Biological insecticide most effective against small, newly hatched larvae. No contact action; larvae must eat treated leaves. Use a spreader-sticker. Some formulations OMRI-listed for organic use.
  • Beauveria bassiana (BontaniGard ES - live spores of an insect-killing fungus)-See label for rates. PHI 0 days. Typically requires 7 to 10 days after first spray to see control. Begin treatment at first appearance of pest. Reapply as necessary. OMRI-listed for organic use.
  • Chromobacterium subtsugae (Grandevo, Grandevo PTO, Grandevo WDG - insect-killing bacterium) at 0.3 to 0.9 lb ai/a. REI 4 hr. Must be mixed with water and applied as a foliar spray with ground or aerial equipment for conventional spraying or by chemigation. OMRI-listed for organic use.

Management-chemical control

  • azadirachtin-Some formulations are OMRI-listed for organic use.
    • (Azatin XL) at 0.01 to 0.033 lb ai/a. Foliar application against larvae.
    • (Azatin O) at 0.025 to 0.1 lb ai/a. Foliar application against larvae.
    • (Aza-Direct) at 0.0123 to 0.024 lb ai/a and up to 0.0432 lb ai/a under extremely heavy pest infestation.
    • (Debug Tres) at 0.0375 to 0.1054 lb ai/a
    • (Ecozin Plus) at 0.012 to 0.023 lb ai/acre. Spray when pests first appear and repeat after 7-10 days.
  • alpha-cypermethrin (Fastac CS) at 0.014 to 0.025 lb ai/a. PHI 50 days. REI 12 hr. Apply by air or ground equipment using sufficient water to obtain full coverage of foliage (minimum of 2 gallons per acre by air and 10 gal per acre by ground). Apply no more than 0.075 lb ai/a per season. Do not graze or harvest treated sugar beet tops for livestock feed.
  • azadirachtin + pyrethrins (Azera) at 0.0125 to 0.025 lb ai/a, and up to 0.044 lb ai/a under extremely heavy infestation. Dilution in a minimum of 30 gal of water per acre is recommended for conventional equipment. May be applied by air at the rate of 0.0125 to 0.025 lb ai/a in a minimum of 25 gal of water. Do not repeat more than every 5-7 days. OMRI-listed for organic use.
  • Burkholderia spp. (Venerate XC - heat-killed insecticidal bacteria)-See label for rates. PHI 0 days. REI 4 hr. OMRI-listed for organic use.
  • carbaryl (Carbaryl 4L, Sevin 4F, Sevin 5 Bait, Sevin XLR Plus, Sevin RP4, Sevin 80 Solupak, Bran For Grasshoppers, and others) at 0.6 to 1.5 lb ai/a. PHI 28 days. For Carbaryl 4L, Sevin 4F, Sevin 5 Bait, and Sevin XLR Plus, do not apply more than a total of 3 lb ai/a per crop. For Sevin RP4, do not apply more than a total of 4 lb ai/a per crop. For Sevin 80 Solupak, do not apply more than 4 lb ai/a per crop. For Bran for Grasshoppers, do not apply more than 1.2 lbs ai/a per crop. OMRI-listed for organic use.
  • chlorantraniliprole (Coragen) at 0.045 to 0.065 lb ai/a. PHI 1 day. REI 4 hr. Apply no more than 4 applications per crop, no more than 0.2 lb ai per acre per year. Minimum interval between treatments is 3 days.
  • chlorpyrifos-
    • For yellowstriped armyworm (several methods):
      • (Eraser, Govern 4E, Lorsban 4E, Lorsban 75 WG, Nufos 4E, Pilot 4E, Warhawk, Whirlwind, Yuma 4E, and others) at 0.5 to 1 lb ai/a broadcast -or- Lorsban Advanced, Vulcan at 0.469 to 0.939 lb ai/a broadcast. PHI 30 days. Do not allow livestock to graze in treated areas or harvest treated beet tops as feed for meat or dairy animals within 30 days after last treatment.
      • (Eraser, Hatchet, Govern 4E, Lorsban 4E, Lorsban 75 WG, Nufos 4E, Pilot 4E, Warhawk, Whirlwind, Yuma 4E, and others) at 0.33 to 0.67 lb ai/a band -or- Lorsban Advanced, Vulcan at 0.313 to 0.626 lb ai/a band. Apply as a 5- to 7-inch band, lightly incorporating mechanically or with irrigation.
    • For beet armyworm (several methods):
      • (Chlorpyrifos 4E, Eraser, Govern 4E, Lorsban 4E, Lorsban 75 WG, Nufos 4E, Pilot 4E, Warhawk, Whirlwind, Yuma 4E, and others) at 0.75 to 1 lb ai/a broadcast -or- Lorsban Advanced, Vulcan at 0.704 to 0.939 lb ai/a broadcast.
      • (Eraser, Hatchet, Lorsban 4E, Lorsban 75WG, Nufos 4E, Pilot 4E, Warhawk, Whirlwind, Yuma 4E, and others) at 0.5 to 0.67 lb ai/a -or- Lorsban Advanced, Vulcan at 0.469 to 0.626 lb ai/a. Apply as a 5- to 7-inch band, lightly incorporating mechanically or with irrigation.
  • esfenvalerate (Asana XL, S-fenvaloStar, Zyrate) at 0.03 to 0.05 lb ai/a. PHI 21 days. Aids in control. Apply as necessary but do no more than 0.15 lb ai/a per season. Apply with ground or air equipment using enough water to cover uniformly (at least 2 gal/a water).
  • garlic oil (Garlic Barrier AG+)-See label for rates. Apply as preventive repellent treatment prior to insect infestation. Make first application at crop emergence and repeat on a 10 to 14 spray schedule to maintain repellency effect.
  • horticultural oil (BioCover and others)-See label for rates. PHI 0 days. Some formulations are OMRI-listed for organic use.
  • methomyl (Annihilate LV, Annihilate SP, Corrida 29 SL, Corrida 90 WSP, Lannate LV, Lannate SP, Lemur, M1 LV, M1 SP, Nudrin LV, Nudrin SP) at 0.225 to 0.9 lb ai/a. PHI for roots 21 days or 30 days if tops are fed to livestock. REI 48 hr. Do not apply more than 4.5 lb ai/a per crop. Do not apply more than 10 times per crop. May be applied by overhead sprinkler chemigation to control beet armyworm and western yellowstriped armyworm, in which case highest listed rate should be used with 0.1 to 0.2 inches of water per acre.
  • methoxyfenozide (Intrepid 2F, Troubadour) at 0.12 to 0.25 lb ai/a. Apply at egg hatch or when signs of feeding occur. PHI 7 days.
  • mineral oil (470 Supreme Spray Oil and others)-See label for rates. Do not exceed 3 gal of this product per acre. Some formulations are OMRI-listed for organic use.
  • naled (Dibrom 8 Emulsive) at 0.94 lb ai/a. REI 48 hr. PHI 2 days. Recommendation as permitted under FIFRA Section 2(ee). Do not apply more than 4.7 lb ai/a per season.
  • pyrethrins (Lynx EC 1.4, Lynx EC 5.0, PyGanic EC 1.4, Tersus)-See label for rates. REI 12 hr. PHI 0 days. Some formulations are OMRI-listed for organic use.
  • pyrethrins and piperonyl butoxide (Evergreen Crop Protection EC 60-6, Pyrenone, Pyronyl Crop Spray, and others)-See label for rates.
  • sodium tetraborohydrate decahydrate (Prev-Am Ultra) applied as a 0.4% solution for beet armyworm only, 40-50 gal/a. Spray every 7 to 10 days as necessary.
  • soybean oil + garlic oil + Capsicum oleoresin extract (Captiva)-See label for rates. PHI 0 days. REI 4 hr. OMRI-listed for organic use.
  • spinosad
    • (Blackhawk) at 0.051 to 0.079 lb ai/a. Do not apply fewer than 7 days apart. Do not apply more than 0.33 lb ai per crop. PHI 3 days.
    • (Entrust, Entrust SC) at 0.075 to 0.15 lb ai/a. Do not apply fewer than 7 days apart. Do not apply more than four times per crop or apply more than 0.33 lb ai/a per crop. PHI 3 days. OMRI-listed for organic use.
    • (Radiant SC) at 0.05 to 0.0625 lb ai/a, excluding western yellowstriped armyworm. Do not apply more than 0.25 lb ai/a per crop. PHI 7 days.
    • (Success) at 0.025 to 0.05 lb ai/a. Do not apply more than four times per crop or 0.45 lb ai/a per crop. PHI 3 days.
  • triphenyltin-hydroxide (Agri Tin)-See label for rates. For suppression only. REI 48 hr; PHI 21 days.
  • zeta-cypermethrin-
    • (Mustang) at 0.028 to 0.05 lb ai/a. PHI 50 days. Do not apply more than 0.15 lb ai/a per season (at planting + foliar applications). Apply with ground or air equipment using enough water to fully cover foliage.
    • (Mustang Maxx) at 0.014 to 0.025 lb ai/a. 50 day PHI for tops or roots. Do not apply more than 0.075 lb ai/a per season. REI 12 hr. Apply by air or ground using minimum of 2 gal per acre by air and 10 gal per acre by ground.