White Pine Weevil

Dec 4, 2023 | Gardening Advice

The white pine weevil (Pissodes strobi Peck), which kills the tops of conifers, is the most serious insect pest of the white pine (Pinus strobus), in Maine.

HOST TREES: The weevil also attacks: Norway Spruce (Picea abies), Colorado Blue Spruce (Picea pungens), jack pine (Pinus banksiana), Scotch Pine (Pinus sylvestris), Swiss Mountain Pine (Pinus mugo), and native spruces. Weevils do not usually attack trees less than 4 or 5 years old, or less than 3 feet tall.

LIFE CYCLE: The white pine weevil has one generation per year. In early spring, adults emerge, feed, mate, then lay eggs in the tree bark. Eggs hatch in about 10 days and the larvae feed on the inside of the leader. Pupation occurs in the leader and new adults emerge in August and September. Adults feed and by November, all weevils have entered the ground litter where they over-winter.

SYMPTOMS OF ATTACK: The first symptom of weevil attack is resin oozing from small feeding punctures in May and June. Punctures are usually found near the top of the previous year’s leader. Wilting leaders may be detected in June and July. After that, needles on the dead portion of the leader will turn yellowish-green, then reddish, and fall off. Typically 1½-2 feet of the main stem is killed. Finally, adult exit holes (2-3 mm) will be left on the leader in August and September.

CONTROL: Mechanical control may be achieved by prompt removal and burning of infested leaders before weevils emerge reduces the chance of population buildup. Prune infested leaders, early in the season, at a point below the tunneling grubs and include some green bark below the tunneling grubs. Immediately burn cut leaders to destroy the larvae and pupae. Chemical control is achieved by treating the terminal leader with a registered insecticide such as permethrin before the buds open. Apply the insecticide no later than late March or early April. For valuable specimen trees, it may be necessary to treat each year.

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