Cranberry-Blackheaded fireworm

Rhopobota naevana

Pest description and crop damage This insect overwinters in the egg stage on undersides of cranberry leaves. Larvae are greenish yellow with a shiny black head, and are 0.25 inch long at maturity. First-brood larvae web and feed on new tip growth in late April or early May. Second-brood larvae web runner ends and damage berries and fruit buds for next year's crop. When injury is severe, vine tips look brown, as if scorched by fire, and berries shrivel. A third generation of moths may emerge in August and September. Moths of the second and third broods lay overwintering eggs.

Sampling and thresholds In late April, begin to monitor for larvae that have hatched from overwintering eggs by using a sweep net or by doing a visual sweep. A visual sweep consists of 10 visual inspections of two square feet per acre. Treatment is recommended if one larva per sweep net or visual sweep is found. Control of the first larval hatch helps reduce likelihood of large subsequent hatches. Pheromone traps are available to monitor flight activity of the moth stage.

Management-chemical control: COMMERCIAL USE

  • acephate (Orthene 97 and Acephate 97UP) at 1.0 lb ai/a. PHI 75 or 90 days (check label). Do not apply during bloom; material is hazardous to bees. Do not exceed one application per crop season. Do not tank mix with other organophosphate insecticides.
  • Bacillus thuringiensis kurstaki (Btk) (Crymax, DiPel DF, Biobit, Xentari and others)-Consult label for rate. PHI 0 days. Not effective for second generation larvae. Some formulations are OMRI-listed for organic use. Most effective when applied multiple times and in low gallonage against small caterpillars feeding on foliage. Scouting for early larval emergence is critical. Well-timed chemigation systems are critical for good efficacy (6 minutes or less rinse time). Thorough coverage is essential and repeat applications may be necessary. Caterpillars stop feeding after eating compounds but may take several (3-10) days to die. Use low-volume ground applications when possible to improve performance.
  • carbaryl (several brands) at 1.5 to 2 lb ai/a. PHI 7 days. Do not apply during bloom; carbaryl is hazardous to bees. Latex-based formulations such as Sevin XLR Plus are less hazardous to bees.
  • chlorantraniliprole (Altacor) at 0.066 to 0.099 lb ai/a. PHI 1 day. Apply just prior to egg hatch or to small larvae. Repeat application 14 to 20 days later. Do not exceed 2 consecutive applications of chlorantraniliprole (Group 28 insecticides) or > 0.198 lb ai per crop season.
  • chlorpyrifos (Lorsban) at 1.41 lb ai/a. PHI 60 days. Do not apply to bloom; material is hazardous to bees. Do not exceed two applications per season. Restricted use material in the Grayland cranberry-growing area of Washington.
  • Chromobacterium subtsugae (Grandevo or Grandevo WDG) at 1 to 3 lb/a (consult label for exact rate). PHI 0 days. Two applications are required to achieve adequate suppression. Temporarily repels honey bees for up to 4-6 days after spraying. OMRI-listed for organic use.
  • diazinon (several brands) at 2 lb ai/a. PHI 7 days. Do not apply to bloom; material is hazardous to bees. Restricted use material in the Grayland cranberry-growing area of Washington.
  • indoxacarb (Avaunt) at 0.11 lb ai/a. PHI 30 days (7 days for Avaunt evo). Material is hazardous to bees.
  • methoxyfenozide (Intrepid and others) at 0.16 to 0.25 lb ai/a. PHI 14 days. Apply to small larvae. Repeat application 10-14 days later. Do not exceed 1 lb ai/a per crop season.
  • phosmet (Imidan) at 0.9 to 2.8 lb ai/a. PHI 14 days. Allow at least 10 days between applications. Do not exceed 10.92 lb ai/a per crop season. Do not apply during bloom; material is hazardous to bees.
  • pyrethrin (several brands)-Consult label for rate and use directions. PHI 0 days. Apply to small larvae. PyGanic brand is OMRI-listed for organic use. Do not apply to bloom; material is hazardous to bees.
  • spinetoram (Delegate) at 0.05 to 0.09 lb ai/a. PHI 21 days. Apply at egg hatch or to small larvae. Repeat applications should not be made less than 7 days apart. Do not exceed 6 applications per season. Do not apply to bloom; material is hazardous to bees for three hours following treatment.
  • spinosad (Entrust) at 0.06 to 0.09 lb ai/a. PHI 21 days. Apply at egg hatch or to small larvae. Entrust is OMRI-listed for organic use. Do not apply to bloom; material is hazardous to bees for three hours following treatment.
  • tebufenozide (Confirm) at 0.25 lb ai/a. PHI 30 days. Apply at first sign of larval infestation during first generation of the season; repeat application 7 to 10 days later. For second generation, apply at 10 to 20% egg hatch; repeat application 7 to 10 days later. Do not exceed 1 lb ai/a product per crop season.

Management-cultural control

Short-term (24 to 48 hours) spring flooding just prior to or during egg-hatch can reduce populations of the first generation fireworm larvae. Water level must be maintained above vine tips.