Have you noticed holes in the trunk or main branches of your fruit trees? Even if these insects aren’t the direct cause of death in fruit trees or destruction of crops, they open them up to infection from other diseases, fungi, & pests. Here’s a few of the worst offenders & how to deal with them.
Peach Tree Borer (moth)
Most affected trees: peach, apricot, plum, cherry
Peachtree borer larvae primarily attack tree trunks just at or below the soil line, but may enter trunks up to 12 inches above the ground. Larvae tunnel between the inner bark and sapwood in the cambium, often girdling and killing young trees in one season. Older trees may withstand the damage, but will be predisposed to attack by other insects and diseases and can be killed after several years of infestation. Visual symptoms include dead bark peeling off of damaged areas and masses of gummy sap mixed with sawdust and frass exuding from entry and exit holes. Leaves of affected limbs will turn yellow and wilt and the tree canopy will eventually die back. Active season starts in July and may run through the fall.
There are a number of strategies to deal organically with the peach tree borer:
1. Find the entry holes near base of trunk and stab individual larvae with a length of wire inserted into their burrows.
2. Cultivate soil around base of trunk in fall and spring to kill larvae and pupae.
3. Rub off loose bark and saturate trunk with neem oil spray. Or add diotomaceous earth or plaster of paris to a trunk whitewash.
5. Spraying Bacillus thuringiensis (Bt) during bloom time is a last-resort organic option, but timing must be good, and check with other gardeners because some people are opposed to its use. It is generally recommended to spray twice during bloom time. Bloom sprays are preferred over in-season sprays in an Integrated Pest Management (IPM) program because they have less adverse impact on beneficial insects and nontarget organisms, and they do not leave a residue on fruit.
Roundheaded Appletree Borer, Shothole Borers & Ambrosia Beetles (beetle)
Most affected trees: apple, pear, cherry, & plum
The Roundheaded Appletree Borer (Saperda candida) is a yellow or reddish brown beetle with a white grub that burrows into the base of trunks in a similar way to Peachtree borers. The shothole borer (Scolytus rugulosus) is a bark beetle that lives between the bark and the surface of the wood, scoring the sapwood. It feeds on the tree’s succulent phloem tissue. Ambrosia beetles bore into the wood of trees, forming galleries in which both adults and larvae live. They feed on an ambrosia fungus, which they cultivate.
Sawdust or frass near the base of the trunk is a sure sign of the Appletree borers. All of the techniques described above for Peachtree Borer can be applied to these beetle borers as well. Check out the great and detailed look at organic controls for borers by orchard guru Michael Phillips: https://www.youtube.com/watch?v=jgYxuWF-fmg
All shothole borers and ambrosia beetles are attracted to injured or stressed trees. Because chemical controls have not proven very successful, the best management approach is to keep trees healthy with adequate watering & feeding, & to keep prunings & diseased or infested wood far away from your orchard site. In winter, remove and burn infested and diseased trees or branches of both orchard trees and other nearby hosts. http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=530
This edition of POP TIPS prepared by POP’s Education & Outreach Director Robyn Mello.
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