Willows are trees and shrubs in the Salix genus grown in cold to temperate climates. Valued for their ornamental appeal, willows grow through much of the North America. However, willows are susceptible to a variety of small black insects that infest willow wood. Damage from these infestations can range from mild to severe if left uncontrolled. Early identification and control are vital for reducing the damage caused by these insect pests.
The flathead borer is a beetle that burrows within willow wood to lay eggs. The beetle ranges in colour from copper to black. The insect favours willow wood weakened by sunburn, disease or pruning damage. The borer tunnels beneath the bark and into the wood, causing small holes, sawdust-like shavings around the infested area and a sappy build-up around the entrance of the tunnel. Heavy populations of the flathead borer on willow can lead to limb and tree death. Maintain tree vigour with regular watering and fertilisation. Avoid pruning during the spring and summer to prevent infestation, states the website of the University California, Davis. Insecticidal sprays are an effective method of control for adult borers during the spring. However, insecticides are not effective for controlling larvae.
The beaked-gall midge is a small fly that tunnels within willow wood to lay eggs. The black fly tunnels through willow leaf buds during the spring to lay eggs. The larvae feed on plant tissue once they emerge from their eggs, which cause red galls to appear in the infested area during the summer months. While the damage may seem severe, the galls rarely create more than a cosmetic blemish to otherwise healthy willows. However, perennial infestations may cause distorted growth. Prune and destroy infected branches to control the beaked-gall midge.
The willow borer is a small, black weevil that can cause severe damage to willow wood. The adult weevil measures a third of an inch and emerges during the spring months. The female weevil burrows into the wood of stems during the summer months to lay eggs. Once the eggs hatch, the larvae tunnel within the wood, creating sawdust-like shavings around the infected hold. The tunnelling causes weakened tree limbs, dead patches of bark, visible holes in the bark and young tree death. Insecticides are an effective method for controlling the willow borer.
Giant Bark Aphid
The giant bark aphid is the largest species of aphid to infest willow trees, measuring a quarter-inch long. The aphid is a small black insect that uses an elongated mouthpiece to suck nutrients from willow wood. Damage from severe infestations consists of twig death, branch death and honeydew deposits. Honeydew is a byproduct secreted by feeding aphids, which attracts the sooty mould fungus and other small insects. However, mild to moderate infestations rarely cause significant damage to mature willow trees. Insecticidal control is effective for severe populations of aphids.