Grass seed-Billbug

East of the Cascades, in bluegrass:

Bluegrass billbug (Sphenophorus parvulus)
Denver billbug (Sphenophorus cicatristriatus)

West of the Cascades, in orchardgrass:

Western orchardgrass billbug (Sphenophorus venatus confluens)

Pest description and crop damage The following description is of the western orchardgrass billbug, a common billbug in grasses, for which we have the most biological knowledge: Adults are beetles about 0.5 inch long, black to dark brown, with mandibles extended into a fairly long "snout." Elbowed antennae insert near the end of the snout. The body is covered with small punctations and irregular-size pits, as if poked with needles. Adults feed on developing leaves while the leaves are still folded longitudinally and close to the crown. As the leaves grow and elongate in the spring (March and April) and in the fall (October), distinctive, paired feeding holes about 0.25 to 0.33 inch in diameter become apparent. Larvae are legless, very plump, dirty white with chestnut brown heads, and mature usually in August. The small, white, oval eggs are about 0.03 inch long and are inserted individually into stem or crown tissue in the spring. The pupae progress from white to tan to brown, are shaped much like the adults, and are found in the soil with plant crowns in July and August. Larvae severely damage orchardgrass; tunneling up stems and into crowns. Heavy infestations may destroy entire plants, or fields, in one season. Yields are affected drastically, and stands decline and become unproductive if billbugs are not controlled.

Biology and life history Eggs are deposited in crown and stem tissue from late April or early May through June. They hatch in 2 to 3 weeks. Larvae feed in plant stems until they outgrow them: then they feed and develop in crown and root tissue. Mature larvae are found in crowns and roots as well as in adjacent soil.

Western orchardgrass billbug begins pupation in late July or early August. About 90% of pupae transform to new adults by mid-October. These adults feed for a week or two on fall regrowth at the crown and are tightly wedged among the shoots of the plant crown. Adults may wander through the field for a week or two before becoming inactive and hibernating in crowns.

There is one generation per year. Bluegrass billbug also has one generation per year, but the development stages are slightly faster than those of the orchardgrass billbug.

Scouting and thresholds Orchardgrass billbug-Walk orchardgrass fields from late March through early April (spring control of adults) and again from mid-October through early November. Carefully inspect at least 200 randomly selected crowns as you walk. If you see any adult feeding holes on even a single leaf of a crown, mark the crown "infested." The treatment threshold is adult feeding damage in 6 to 10% of crowns. Initial infestations may begin at field margins, but within a year may spread throughout the field. If you notice a small amount of feeding damage on field edges, spray the infested border areas.

Management-cultural control

Orchardgrass billbug-Postharvest open-field burns kill less than 35% of the adults present at the time. Further, the burning orchardgrass fields that have been moderately to severely injured can result in stand loss, because the greatly weakened plants often die as a result of the fire.

Crop rotation-This billbug does not injure other grass species, even though small numbers often are found in bentgrass and bluegrass fields. Adult billbugs will also feed on a wheat crop that follows orchardgrass; however, injury is minimal and generally insufficient to justify control.

Management-chemical control

  • bifenthrin (BrigadeÆ 2EC and WSB) at 0.1 lb ai/A. Apply in early fall and/or spring when larvae are active. Best results are achieved with 25 to 40 gallons of spray solution per acre followed by irrigation or rainfall. Maximum amount allowed is 0.2 lb ai/A per season but no more than once every 14 days. PHI 30 days prior to harvest for forage, hay and seed.
  • chlorantraniliprole (Vantacor) at 0.066 to 0.098 lb ai/A (1.7 to 2.5 fl oz/A). PHI is 0 days. REI 4 hr.
  • lambda-cyhalothrin (Warrior) at 0.02 to 0.03 lb ai/A. Suppression only. PHI 0 days for grazing and forage, 7 days for straw and seed crop. REI 24 hr.
  • lambda-cyhalothrin/chlorantraniliprole (Besiege) at 6.0 to 10.0 fl oz/A. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr. Suppression only. Do not exceed a total of 27.0 fl oz of Besiege or 0.09 lb ai of lambda-cyhalothrin or 0.2 lb ai of chlorantraniliprole per acre per year.
    • Unirrigated crops-Apply in early April during rain. Spring rain is absolutely necessary to move product to plant crowns where adult billbugs are active. Fall application-Apply after Oct. 15 and before Nov. 7, when adults are active and moving among plant crowns prior to hibernation. Treating at this time may provide better control than applications made in spring because re-growth is slight and rain is not as critical to move chlorpyrifos to the crowns of plants.
    • Drop or flood nozzles that direct streams of insecticide to crowns tend to provide better control than nozzles that broadcast spray. Charcoal on the soil surface (from previous field burns) and/or a heavy postharvest straw load in the field and on plant crowns will tie up chlorpyrifos or any other insecticide-resulting in virtually no pest control. RESTRICTED USE IN OREGON.