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In the Spotlight ... Borers
In this section of the Vermont Apple Newsletter, a
different arthropod or disease is featured. This information is part of
"Key Arthropods, Diseases, and Vertebrates affecting Apples: A
Synopsis" by Jessica Reardon and Lorraine Berkett and which appeared in the
Back to Basics Resource Notebook, March 22, 2000.
Borers
Dogwood borer
Synanthedon scitula (Harris)
Roundheaded apple tree borer
Saperda candida (Fabricus)
Description: The dogwood borer adult is a black and yellow striped
clear winged moth that resembles a wasp. The larva is pale pink with a brown head. Adult round-headed
apple tree borers are light olive brown beetles, with two white stripes running the
length of the body. The females are approximately 1 inch long, the males slightly smaller.
Larvae are pale yellowish white, with a dark brown head and dark mandibles.
Dogwood borers overwinter as full-grown larvae under bark.
The insect pupates in the spring and the adults emerge in June, continuing to emerge
through July and often early August. Round-headed apple tree borer adults deposit
eggs under bark and in small cavities in the tree trunk, near the ground. The larvae
hatch, and bore into the tree, eventually reaching the heartwood. The larvae pupate and
emerge as adults two to three years later.
Damage: Dogwood borers bore into burr knots or adventitious roots just
below the graft union. Insects are detectable by the presence of reddish brown frass on
the surface of the bored wood. Presence of round-headed apple tree borers is
detectable by sawdust casting pushed from the on the ground beneath bored tunnels.
Key times for monitoring: spring and bloom (dogwood borer). September
(roundheaded apple tree borer)
Monitoring method: Wing pheromone traps may be used for monitoring adult male
emergence of dogwood borer. Traps should be installed during bloom. Traps may be baited
with either dogwood borer pheromone or lilac borer pheromone. Research in Virginia has
shown that traps baited with the lilac borer pheromone are actually more effective at
catching dogwood borer than traps baited with the dogwood borer pheromone. Traps should be
hung at four feet above the ground. Height of trap placement is critical - deviations may
drastically reduce trap capture. Traps for dogwood may also capture other borers, as these
traps are not very species specific. There are currently no action thresholds for dogwood
borer. In the spring, check under tree guards for active infestations of dogwood borer. If
burr knots on the tree are noticed, they should be examined for the presence of the
protruding pupal skins of the dogwood borer. To monitor for the presence of round headed
apple tree borer, look for reddish sawdust-like castings at the base of the tree and
darkened areas in the bark in September.
Keep trees healthy. It has been found that
regularly watered and fertilized trees are able to maintain vigor and are less susceptible
to borer injury, while stressed trees are more susceptible to borer attack.
Select rootstocks with a lower propensity for burr knots. Keep the area around
the trunk weed-free and do not mulch around tree trunks. Use wire mesh rather than solid
plastic mouse guards. Apply white latex paint to the trunk area to deter egg laying.
Severely attacked trees should be removed.
Monitor for round-headed borer presence in September. If presence of round-headed
borer is noticed, a small length of wire can be inserted into tunnels to kill larvae.
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