APPLE TREE BORER
Apple Root Borers feed on the wood of trees, affect fruit trees including apples, cherries, peaches, pears and plums. Several species of insects bore into apple trees, including roundheaded apple tree borer, flatheaded apple-tree borer, and broad-necked root borer. It attacks healthy young trees, boring into trunks and often causing tree death. The immature or larval stages of insects, particularly beetles and moths that feed on wood rather than leaves or plant juices are referred to as borers. All the woody parts of the tree from the buds and twigs to the trunk and roots are susceptible to borer attack. Most borers are attracted to trees that are weakened through drought, injury or disease, but some borer species can successfully attack healthy, vigorous trees. Once borers have infested a tree, they can be difficult to control. Insecticidal sprays can be successful only if they are applied to the tree when the adult borers are active and laying eggs. Consequently, the proper timing of insecticide sprays is crucial for effective chemical control of borers.
- ROUND-HEADED APPLE TREE BORER ( SAPERDA CANDIDA)
- FLAT-HEADED APPLE TREE BORER (Chrysobothris femorata)
- BROAD-NECKED APPLE TREE BORER (Prionus laticollis)
ROUND-HEADED APPLE TREE BORER
This is the most serious borer among apple trees. The adults are striking brown-and-white-striped beetles, almost an inch long. The females lay eggs from early June through August in bark crevices in the lower two feet of the trunk. Upon hatching, the larvae bore into the tree and begin feeding on the outer bark, gradually getting deeper and boring into the wood. Young larvae sometimes bore into wood below the ground surface, but older larvae feed above ground. It takes two to three years to complete the life cycle. Adult beetles are nocturnal and feed on leaves and occasionally fruit, but are not considered economically important. They are active from early May to September, with females depositing eggs under bark and in small cavities in the tree trunk near the ground. Peak egg laying activity takes place in June. A single larva can kill a young tree. The life cycle requires two to three years before the larvae pupate and emerge as adults.
Round-headed apple tree borers are capable of attacking young and healthy trees. Larvae feed on the cambial tissue near the base of the tree by boring into the branches and the trunk. Presence of larvae is indicated by sawdust castings pushed from the tunnel, accumulating on the ground beneath the tunnel entrance. Girdling of young trees eventually results in a greatly weakened tree, often leading to death. Young non-bearing blocks of apple trees are particularly susceptible. The tunnels are round in cross-section and in spring of their second year, the larvae pupate in the tunnel and emerge as adults in summer.
The adult beetle is about 0.5 to 1 inch long with the antennae being about the same length. The body is entirely white except for three broad longitudinal brown stripes extending the full length of the body. The borer has a two-year life cycle. Adult beetles usually appear in May and June, with egg-laying continuing until late July. Eggs typically are inserted into the bark of the trunk near the ground, although eggs may occasionally be laid in tree crotches. The hatched larva begins feeding within the bark and by September, the larvae are found between the bark and sapwood. During this time the larvae eject wood cuttings and a rusty-brown saw dust from their tunnels. By the time winter sets in, the larvae have produced a tunnel about 3 to 4 inches long. The larva passes the winter in the sapwood. During the following spring, summer and fall, the larva bores deeper — 1 to 2 inches — into the wood. A mature larva is about 1.25 inches long, fleshy, thin-skinned, white or yellowish, cylindrically shaped, with a brown head and a rounded thickening of the body just behind the head. In the spring, the larva pupates and passes into the adult stage. The adult escapes from the chamber by cutting away the bark cap. Adults will crawl over the surface of the tree and feed to some extent on the foliage and on the new twig growth. Despite having well-developed wings, the adult beetle usually will fly only short distances.
Regular insecticide treatments applied to control other orchard pests aid somewhat in controlling the round headed apple tree borer. The adults frequently will get enough poison to kill them when feeding on the new bark or leaves. As such, borer infestations usually are worse in neglected orchards. The use of trunk wraps has not been entirely successful.
During August and September, growers should check each tree for the presence of the young larvae, especially in those parts of the orchard where previous infestations have occurred. In nearly all cases the newly hatched larvae will cause some sap flow at the point where they begin to feed. This brown sap stain usually can be seen easily on the surface of the bark. When sap stains are found, a shallow slice in the surface of the bark with a sharp knife will expose or kill the young borer without causing any injury to the tree. At this time it is often possible to locate and destroy, with a flexible wire probed into the tunnel, an occasional second-year borer that may have escaped the previous year’s worming. It is best to worm the trees each year.
For chemical control, licensed pesticide applicators may apply chlorpyrifos, or any other appropriately labeled product as a trunk and lower limb spray. Insecticides available for homeowner use include some formulations of permethrin and imidacloprid. Because adult emergence and egg-laying can occur over a relatively long period, two to three insecticide applications may be needed during June and July. Please read the label carefully for proper rates and application procedures before using any insecticide.