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Adult greater peachtree borers are often mistaken for wasps, but they're actually clearwing moths.

Courtesy Meredith Seaver, USU Extension

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The larvae of the greater peachtree borer are actually the caterpillars of clearwing moths.

Courtesy Meredith Seaver, USU Extension

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Greater peachtree borer larvae feed on the cambium tissue under the bark of stone fruit trees. This feeding can girdle and kill a tree, especially a small tree.

Courtesy Meredith Seaver, USU Extension

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Now that we’re in the last half of June, it’s time to give our stone fruit trees (peaches, apricots, cherries and plums) the protection they need from the greater peachtree borer (GPB). This borer is the moth that causes the gummy oozing on the soil against the trunk and sometimes on the lowest part of the tree trunk.

Female moths lay eggs in bark crevices, and the creamy white larvae bore into the lower trunk as soon as they hatch and feed on the cambium under the bark of the lower trunk and surface roots. They feed for the rest of the summer, overwinter in the tree and resume feeding in the spring, causing further damage to the tree.

These borers pupate in the tree and emerge as adults in late spring and early summer. It’s unlikely you would see one of the adults on your tree, but if you did, it would look more like a metallic blue-black wasp than a moth.

If a tree is young and small, the feeding can easily girdle and kill it. The health and vigor of larger, more established trees can be compromised by GPB feeding. All of the damaging borer activity happens within the protective covering of the bark, out of reach of insecticidal sprays and other control efforts, so prevention is the most important thing you can do.

If you’ve been growing any of the stone fruits for many years, you may be in the habit of simply applying a protective insecticidal spray to your tree trunks at the beginning of July and again at the beginning of August. Insect development is influenced by temperature; the warmer the weather, the faster insects develop. Now, as much of our solid zone 5 valley has warmed into a milder zone, we’ve seen the GPB showing up earlier.

Because the greater peachtree borer is showing up earlier, we need to do the first application in mid-June instead of early July if we want to protect our trees from this borer. You may have already done your first preventive application, but if you haven’t, it’s time to get that done.

Your spray application should protect the lower 10 to 12 inches of the trunk for your stone fruit trees. There is no need to spray the rest of the tree. Ornamental relatives of stone fruits can also be damaged by the GPB and may need protective insecticide applications. Flowering almond, weeping cherry and flowering plum trees are good examples of these ornamental trees. Make sure the spray covers the entire surface area of all your stone fruit trunks, particularly close to ground level and including any exposed roots. Your protective sprays need to continue into September.

Not every insecticide is effective at preventing greater peachtree borer problems. Make sure you choose an effective spray product for your trees. Products with the active ingredient permethrin will provide reliable protection and only need to be applied once a month. Organic gardeners can look for products with the active ingredient pyrethrin or azadirachtin instead. These products must be applied weekly, though.

You may have heard that planting garlic around your trees, spreading moth balls around the trunk or painting the trunk with light-colored paint will stop greater peachtree borers. Research hasn’t shown garlic to be a reliable option, and sprinkling mothballs or moth crystals around the base of the trunk is unsafe. Painting tree trunks with diluted white paint is one way to prevent Southwest winter injury, but it doesn’t discourage borers.

Insecticides shouldn’t be your only tool in keeping GPBs out of your stone fruit trees. The same good tree care habits that give you a flavorful, bountiful harvest can also make your tree less attractive to the greater peachtree borer.

Female borers prefer shaded, secluded areas for egg laying. Keep the area around your trees free of weeds, grass and any other vegetation, and avoid adding excess soil around the base of the tree. The increased warmth and lower humidity from doing this will reduce the survival of eggs and larvae.

Protect the trunks of your trees. Prevent Southwest winter injury, avoid mechanical bark damage and prevent rodent-caused injuries to tree trunks.

Keep your trees healthy with optimal nutrition and irrigation. Apply adequate (but not excess) nitrogen in the early spring. Water your trees deeply and infrequently, ideally not more than once a week during the summer and less often in the spring and fall, to encourage healthy, vigorous root systems.