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ISSUE 10   July 17, 2008

GRASSHOPPERS INCREASING PROBLEM

Field reports indicate that grasshoppers are increasing in numbers in the central and north central regions of North Dakota. Any crop (wheat, barley, corn, sunflowers, flax, ...) is susceptible to attack from grasshoppers. Several conditions that favor a ‘grasshopper outbreak’ have occurred in 2008:

  • Cool and wet early spring prevented premature grasshopper hatch and insured an adequate food supply.
  • Warm and dry late spring promoted uniform hatching time and good weather conditions for feeding.
  • Hot summer with adequate rainfall in some areas of North Dakota have provided good food supply and low incidence of diseases.
  • A sweep net is an easy way to monitor for grasshoppers. In general, four 180-degree sweeps equals one square yard. Note that thresholds are different depending on whether you sample nymphs or adults, or whether you sample from the field margin or from inside the field. Grasshopper thresholds based on numbers of grasshoppers per square yard shown in the following table.

    Grasshopper Thresholds: Infestation Ratings

     

    Nymphs (young hoppers) per square yard

    Adults per square yard

    Rating

    Margin

    Field

    Margin

    Field

    Light

    25-35

    15-23

    10-20

    3-7

    Threatening

    50-75

    30-45

    21-40

    8-14

    Severe

    100-150

    60-90

    41-80

    15-28

    Very Severe

    200+

    120

    80+

    28+

    There have been several inquires as to the status of Mustang Max (zeta-cypermethrin) insecticide on flax for control of grasshoppers this year. We are aware of this critical situation and will keep you posted as soon as more information is available. Since Mustang Max is receiving a full label in flax, we hope to receive a Section 24c instead of a Section 18 before the end of July.

     

    GET READY TO SCOUT FOR BANDED SUNFLOWER MOTH

    Banded sunflower moth is just starting to emerge in our area. NDSU Extension Entomology has had reports of high numbers of banded sunflower moth adults caught in pheromone sentinel traps in extreme southern Manitoba just north of Walhalla, ND. Fields should be monitored for adult moths and eggs when sunflowers are in the R3 (immature bud elongated 0.5 to 2.0 cm above the nearest leaf) stage.

    Description: The adult has a dark band across the buff or yellowish-tan forewings (see photograph). The wingspan is about 0.5 inch. Early instar larvae are off-white; late instar larvae are pinkish to red with a brown head capsule (see photograph). Larvae will be about 0.4 to 0.5 inch at maturity.

    Banded sunflower moth - adult and eggs
    Banded sunflower moth - adult and eggs (right side)

    Banded sunflower moth - larva
    Banded sunflower moth - larva

    Life Cycle: The adults emerge from local overwintering sites rather than migrating long distances. In the northern states the banded moths begin to emerge about mid-July and are present until mid-August. Adults tend to congregate in field margins or adjacent crops during the day and then move into the sunflower crop in the evening. Within a week after emergence they begin to lay eggs on the outside of the flower bracts. Eggs hatch in 5 to 8 days and may be found through early August. Larvae develop through five instars and are present in sunflower heads from mid-July to mid-September. After feeding to maturity, larvae drop to the ground to overwinter.

    Damage: Newly hatched larvae move from the bracts (where they feed initially) to the florets of the sunflower head and enter open florets to feed. During later stages, the larvae tunnel through the bases of the florets into the seeds and consume the contents. Each larva may destroy 5 to 7 seeds. Silken webbing on the face of the head (see photograph) at maturity indicates the presence of larvae within the head.

    Banded sunflower moth webbing

    Scouting: Sampling plans have been developed using both adult and egg counts. Adult moth and egg counts should be made when most of the plants are at the R3 stage (see photograph). A low power magnifier is recommended for egg counts. The new sampling system for adult moths should be conducted during the day (late morning or early afternoon). The moths remain quiet, resting on upper or lower surfaces of the leaves of sunflower plants during the day. When disturbed, they flutter from plant to plant. For details on adult moth and egg scouting and economic thresholds go to Banded Sunflower Moth E-823 (Revised) -. http://www.ag.ndsu.edu/pubs/plantsci/pests/e823w.htm  

    R3 sunflower
    Sunflower at stage R-3

    Control: The economic threshold level has changed with the current high market value. When monitoring for adults during daylight hours, one banded moth per 100 plants is a reasonable threshold given the high 2008 sunflower market prices. For egg counts, the threshold level in 2008 is about 2-3 eggs per six bracts. Chemicals should be applied from the late bud stage (R4) to early bloom (R5.1). Border spraying can be an option. Spraying in early morning or late evening is preferred to minimize the impact of pollinators. Some common control mistakes include: not scouting; waiting too long to spray; and perimeter spraying only and not scouting the interior of the field.

     

    REGIONAL MONITORING NETWORK FOR SUNFLOWER MOTH AND BANDED SUNFLOWER MOTH

    Sunflower moth and banded sunflower moth traps are being monitored on a weekly basis in the sunflower producing areas of the Great Plains from Texas to North Dakota. Insect maps are being produced weekly to provide a general indication of population levels in 2008. Please see the following websites for maps.

    Sunflower moth: The pheromone trap catches for the male sunflower moth does provide a reliable indicator of the economic populations (treatment levels) for sunflowers in the R3-R5 crop stage. The current threshold is >28 moth per trap per week.  

    www.sunflowernsa.com/growers/default.asp?contentID=357

    Banded sunflower moth: The pheromone trap catches for the male banded sunflower moths is not a reliable way to determine treatment thresholds. Therefore, pheromone trapping of banded sunflower moths should be used only to determine whether moths are emerging and present in the area.

    www.sunflowernsa.com/growers/default.asp?contentID=364

    pheromone trap
    Pheromone trap

    Janet J. Knodel
    Extension Entomologist
    janet.knodel@ndsu.edu


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