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ISSUE 3   May 27, 2010


Dingy cutworms have been observed in some pulse, soybean and sunflower fields in northwestern and southeastern North Dakota; however, with the cool temperatures feeding injury has been minimal. With the warmer temperatures, cutworms will be becoming active. So, now is the time to get out and scout before economic feeding injury occurs.

Cutworms are an early season pest that feed on most of the field crops grown in North Dakota. They become active when soil temperature are above 40F. Crops with lower plant populations such as sunflower, peas, or lentils. are most susceptible to cutworm injury. Cutworm feeding activity usually extends from May through the end of June and young emerging plants are the most susceptible stage of crop development. Typical feeding injury symptoms include clipped off plants with the larvae (caterpillars) underneath in the soil, wilted plants or bare patches of ground in localized spots in a field. In peas and lentils, seedling with new sprouts are a good indication of cutworm feeding where the plant was cut and then the plant tried to initiate a new growth (sprouting). Excessive cool, wet soils tend to amplify stand reduction by slowing plant development relative to cutworm feeding. Cool temperatures will also delay the cutworm emergence and development.

The key to successful cutworm control is early detection and knowing your plant population. Cutworm feeding can be noted by cut or wilted plants, leading to bare patches in the field. Cutworms can be found in the soil around cut plants. If the plant population is below recommended, few or no plants can be lost to cutworm feeding. The greater the plant population the more damage can be tolerated without economic yield loss. When spraying insecticides for cutworm control, applications should be made in the evening when cutworms are actively feeding. Wet soil conditions will also improve insecticide efficacy, as cutworm feed near the soil surface in these conditions. Rescue foliar treatments are warranted when cutworms exceed these treatment thresholds by crop:

  • Alfalfa – 4 to 5 or more per square foot (new stands – only 2/sq ft)
  • Canola – 1 per square foot
  • Corn - 3-6% of the plants are cut and small larvae (<3/4 inch) present
  • Peas / Lentils – 2 to 3 cutworms per square meter
  • Small grain – 4 to 5 cutworms per square foot
  • Soybean - one cutworm per 3 feet of row or 20% of plants are cut
  • Sugarbeet - 4-5% cutting of seedlings or 3-5 larvae per square foot in late summer
  • Sunflower - 1 per square fool or 25-30% of plants cut
  • Spraying timing is the most important aspect of controlling cutworms. Insecticides are ideally targeted at the young larvae, which are easy to kill than the larger larvae (>1 inch). Spraying is recommended at night when cutworms are actively feeding. There are questions about tank mixing insecticides with herbicides for early season weed control. However, check labels for compatibility or do a simple ‘jar test’ mixing the insecticide and herbicide. If spraying for weed burn-down and early season cutworm activity, be sure to re-scout the field as cutworms will continue to emerge over a two to three week period. There has been some questions about applying an at-plant insecticide, such as in-furrow or T-band application for control of cutworms. An in-furrow insecticide application is generally not as effective in controlling cutworms as a T-band application. Since cutworms crawl on the soil surface, a 5-7 inch T-band application over the seed furrow would be more efficacy for cutworm control.

    For insecticides registered in North Dakota for cutworm control, consult the 2010 Field Crop Insect Management Guide at:




    Flea beetles (Phyllotreta spp.) have been observed feeding on volunteer canola, wild mustards and spring planted canola and mustard fields (J. Pederson & D. Waldstein, NCREC, Minot, producers NC Region). In the next several weeks, beetles will be emerging in large numbers with the warm temperature forecast (above 57F) and moist soil conditions.

    Based on the 2009 Canola Survey, flea beetles were found in 94% of the fields surveyed. Peak population densities occurred in the west central (McLean County), north central (Bottineau, Ward, Renville and Pierce Counties) and northeastern (Towner County) regions of North Dakota (Fig. 1). Large populations of flea beetles in late summer indicate large overwintering populations and potentially large populations the next spring.

    Figure 1.
    2009 Flea beetle survey in canola, ND (late summer).

    More than 90% of our canola fields receive a commercially applied seed treatments, like Helix XTra or Prosper FX, in North Dakota. These systemic seed treatments can provide protection against flea beetles for about 21-25 days from planting. With the canola seed sitting in the cool soil conditions, or emerged and not growing, systemic seed treatments are not readily taken up into the plant and this may result in reduced insecticide toxicity and residue against flea beetles.

    The take home message is to regularly scout seedling to 6-leaf canola for feeding injury - pitting. An action threshold of 25% injury would justify a foliar spray on top of the seed treatment. Research indicates that the best insecticide strategy for management of flea beetle was the high rate of insecticide seed treatment plus a foliar insecticide applied at 21 days after planting, regardless of planting date. The foliar spray on top of the seed treatment controlled later-emerging flea beetles as the seed treatment residual was diminishing and the crop became vulnerable to feeding injury. The next few weeks will be critical for protecting canola against significant flea beetle damage! For insecticides registered in canola in North Dakota, consult the 2010 Field Crop Insect Management Guide.

    Funding for the canola survey was provided by the Northern Canola Growers Association and CSREES Canola Research fund.



    The USDA APHIS degree day map (Fig. 2) for grasshopper emergence indicates that first hatch is starting in the southwestern region, central Burleigh and Kidder Counties and northern Rollette County of North Dakota. Scout for early instar grasshopper in ditches and field edges.

    Figure 2. USDA APHIS Grasshopper degree day map.



    Scout fields for adults, larvae and defoliation by sampling 10 plants in 5 random locations (50 total plants) and walking in an M-shaped or similar pattern throughout the field.

    Alfalfa weevil adults overwinter in plant debris, woodlots, and ditches. Adults are about ¼ long and a brown snout beetles with a dark stripe on their back (Fig. 3). As temperatures warm up adults migrate to alfalfa fields to lay eggs. Eggs hatch into small alfalfa weevil larvae that are slate-colored. As larvae mature, their color changes to bright green with a white line running down their back, a black head capsule and are about th of an inch long (Fig. 4).

    Figure 3.
    Alfalfa weevil adult (Clemson University-
    USDA Coop. Extension Slide Series, Bugwood.org)

    Figure 4.
    Alfalfa weevil larva (F. Peairs, CSU, Bugwood.org)

    By using degree days with a base of 48 F, the life stages and development of alfalfa weevil can be predicted (see degree day table). Go to the insect section in the NDAWN website:


    and select the degree day base of 48F to determine the accumulated degree days (DD) for your location. See map (Fig. 5) of North Dakota for alfalfa weevil degree day accumulations.

    Figure 5.
    Alfalfa weevil degree day map (NDAWN, NSDU)

    Scout for Alfalfa Weevils

    Stage of Develop-ment

    Degree Days Req. to Complete Indicate
    Life Stage

    Accum. Degree Days
    (base 48 F)


    General Activity




    7 to 14


    1st instar



    21 to 28

    Light leaf feeding

    2nd instar



    Light leaf feeding

    3rd instar



    Major leaf feeding

    4th instar



    Major leaf feeding





    Mating & egg laying

    Field scouting for alfalfa weevil is initiated at 300 DD. Major feeding by the alfalfa weevil larvae will occurs from 430 to 595 DD (2nd - 4th instar). At greater than 600 growing degree days feeding normally stops and adult emerge.

    This year, the majority of alfalfa field will be cut early before alfalfa weevil infestation. So, scouting will be necessary for the second cutting. Management of weevil infested alfalfa stands depends on when the infestation occurs. If the infestation occurs relatively late, when the alfalfa has reached 20 to 25 inches in height, consider taking an early harvest. Small larvae, those less than ¼ inch in length, will drop to the soil and generally die if the soil is dry. If the infestation occurs early, when alfalfa is 10 to 15 inches in height, chemical treatment may be necessary. Insecticide treatment is recommended if two live larvae per stem occur at this stage and/or 35 to 40% of the plants are showing tip feeding. In general, if alfalfa is 7-10 days out from harvest and 35 to 40% tip feeding is present, an insecticide treatment is recommended.

    Remember to check the preharvest interval as these restrictions vary according to the insecticide used and the rate applied. Other factors to consider when selecting an insecticide is its price, potential hazards to honey bees and whether or not it is a restricted use insecticide. To minimize damage to honey bees and native pollinators, apply insecticides during early morning or late evening when bees are back in the hive.

    Janet Knodel
    Extension Entomologist



    A local butterfly watcher reported Monarchs (Fig. 6) in the Fargo area on May 23. We normally expect Monarchs to return to the northern Great Plains in late May to early June. This is an early but not record setting date, the species has been found as early as the May 12. Monarchs suffered significant population reduction over the 2009-10 season at their wintering locations in the montane pine forests west of Mexico City. The combination of habitat loss due to illegal logging operations and seasonal cold weather has reduced overwintering populations to the lowest levels since monitoring began in 1994. Monarchs migrate each year from North Dakota to west central Mexico and back as far as the Gulf States. The progeny of monarchs that left the northern Great Plains last autumn, complete their circuit by this spring flight.

    Figure 6.
    Monarch butterfly (S. Ellis, Bugwood.org)

    Gerald Fauske
    Collection Manager
    North Dakota State Insect Reference Collection



    Degree-day (DD) accumulations for development of sugarbeet root maggot (SBRM) populations are running about normal this year. NDSU Entomology, in cooperation with American Crystal Sugar Cooperative, MinnDak Sugar Cooperative, and Pembina County Extension, is monitoring fly activity using sticky stakes in 44 grower fields throughout the Red River Valley (RRV) this summer. As of May 24, flies have been detected in rural areas in the vicinity of the following communities: Leroy, Glasston, St. Thomas, Auburn, Minto, Oslo, Euclid, Thompson, and Climax. The highest activity, although early, was observed in the St. Thomas and Auburn areas.

    Fly activity will continue to increase during the next few weeks, although rainy and/or breezy weather could keep flies down on the ground and in plant canopies.

    Peak fly activity can occur at any time after the accumulation of 600 DD; however, NDSU research indicates that peak takes place, on average, at about 650 DD. It is important to note that warm weather (around 80 F), and calm to low-wind conditions are most conducive to fly activity. Flies will remain relatively inactive in cool, rainy, or windy conditions.

    An extended forecast of anticipated DD accumulations and associated peak fly activity dates is presented in Table 1. Please note that this is a PRELIMINARY forecast. Prevailing weather conditions during the next couple of weeks will determine the actual date of peak fly activity in beet fields.

    Table 1. Degree-day (DD) accumulation forecast and predicted peak activity dates for sugarbeet root maggot flies in Red River Valley


    Degree Day
    (for May 27)

    Peak fly
    activity forecast*

    Cavalier, ND


    June 11-17 + 80 day

    St. Thomas, ND


    June 10 -16 + 80 day

    Grafton, ND


    June 10 -16 + 80 day

    Warren, MN


    June 9 -15 + 80 day

    Grand Forks, ND


    June 8 -14 + 80 day

    Hillsboro, ND


    June 6 -12 + 80 day

    Perley, MN


    June 6 -12 + 80 day

    Sabin, MN


    June 5 -11 + 80 day

    *Peak fly activity in current-year beets is most likely on the first calm or light-wind day to reach 80 F after the required 600 air DD are accumulated.

    Fly emergence and movement into beet fields can be accelerated quickly following a major increase in air temperatures. Growers in high-risk areas for SBRM infestation should consider applying a postemergence insecticide, especially if a low or moderate rate of an at-plant soil insecticide was applied. Growers preferring granular products should apply them immediately or as soon as soil moisture conditions allow. It is better to err on the early side of peak activity when applying granules. Postemergence liquid insecticides should be applied within 3 days of the expected peak (before peak is best). This will provide control of both adults and larvae.

    Table 2 presents target DD accumulations for making region-specific postemergence insecticide applications. The recommendations are also based on whether a granular or liquid insecticide will be used. To determine DD accumulations for a specific location, consult the new NDSU Root Maggot Model application on the NDAWN website at:


    Table 2. Area-specific suggested timing to apply postemergence liquid or granular insecticides for SBRM management in the Red River Valley.


    Target DD for Insecticide Applications*

    Liquid Insecticide

    Granular Insecticide

    Northern RRV



    Central RRV



    Southern RRV



    For more guidance on postemergence control strategies, consult the "Insect Control" section of the 2010 Sugarbeet Production Guide or the "Sugarbeet Insects" section of 2010 Field Crop Insect Management Recommendations. Online versions of these publications are located at:




    Mark Boetel
    Research & Extension Entomologist

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