Garden Help Desk: Oozing from stone fruit trees likely caused by borer
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- Grass and vegetation against the trunk of a stone fruit tree provides a humid and secluded place for female borer moths to lay their eggs. Grass against a trunk also increases the likelihood of string trimmer damage and disease problems. Protect your trees by keeping grass and other vegetation a minimum of 2 to 3 feet away from the trunk.
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- Gumming and oozing are signs that something is wrong with a tree — insect activity, disease or environmental stressors such as poor care.
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- Greater peachtree larvae feed under the bark of stone fruit trees and their ornamental relatives. This feeding weakens the tree and can even girdle and kill a tree.
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- Cytospora canker is a fungal disease that kills vascular tissue under the bark and weakens a tree, making the tree susceptible to many other problems. The cankers can eventually expand and girdle a tree.
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- The scarring, cracking and deformities on these nectarines are the result of thrips feeding during bloom.
We definitely have peach tree borers in our nectarine tree. The trunk is pretty much encircled by the sap oozing just above the ground level. What insecticide should I apply to the trunk and saturate the ground with? When is the best time to do so? When I pruned this year, there were at least eight dead branches, is there a possibility of still saving the tree?
There are several potential causes for gumming or oozing sap on stone fruit trees. Sometimes, pests or diseases cause the oozing, but environmental issues can also be the cause. Wounding caused by wildlife or pets (dog chewing/cat scratching), branches rubbing in the wind, hail, frost cracks or sun scald/Southwest winter injury can all result in oozing bark.
Poor management practices like overwatering, hard summer pruning, planting too deeply or letting the tree carry a very heavy fruit load may also cause the problem.
Gumming or oozing on the lower 12 inches of the trunk or at the soil line is most likely caused by the Greater peachtree borer, and that’s probably what has happened with your tree. The borer is the larva of a clearwing moth that looks more like a wasp. Eggs are laid on the lower trunks and roots of stone fruit trees (peach, cherry, apricot, plum) and the larvae burrow into the bark as soon as they’ve hatched. They feed under the bark and cause oozing, yellowing or wilted leaves, and dead bark.
Larval feeding can girdle and kill trees. Younger trees have the greatest risk, and repeated infestations can weaken or kill older trees as well.
There aren’t any sprays that can solve the problem once borers are in a tree, and attempts to dig out a borer can cause damage and leave access into the tree for diseases like Cytospora canker, so it’s important to prevent borer infestations. Mid-June, not springtime, is the time for preventive insecticide applications, and we’ll include information about that in an early June column.
Sometimes borers can be killed by pushing a wire into their entry holes. When there is gumming at the base of the tree, borers can often be found and removed by pulling back gummy masses and several inches of soil around the trunk and carefully checking the trunk and large roots for the larvae. The larvae are plump and white to pinkish-white with dark heads.
Good tree care such as keeping grass and other vegetation away from the base of the trunk; deep, but not frequent watering; and removing tree wrap in the spring instead of leaving it on all year round can all be helpful in making your trees less attractive to the Greater peachtree borer.
Cytospora canker, a fungal disease, can also cause oozing on stone fruit trees. Unlike the greater peachtree borer, Cytospora canker oozing can occur in the upper trunk and branches. The disease can cause sunken, oozing cankers in the bark of the tree. The cankers can expand over time and girdle branches, killing them. This disease gets into trees through wounds in the bark. Wounds from pruning, string-trimmer damage, broken branches, insect damage and sunscald injury can all provide entry points. Stressed trees are especially susceptible.
Pruning out infected branches can sometimes save a tree, but it is more common for trees to decline and eventually die. Once the Cytospora fungus is in the tree, there isn’t an effective chemical treatment, so prevention is important. Protect trees from sun scald and winter injury by using tree wrap during the winter. Keep the area around the trunks free of vegetation so that string trimmers aren’t used near the trees. Make clean pruning cuts and avoid leaving stubs so that cuts can close over more quickly.
For trees with Cytospora cankers, the best course of action is to maintain tree vigor with deep, infrequent watering and appropriate fertilizer in the spring.
No matter the cause of gummy oozing in a home orchard, good tree care from year to year will make a big difference in how susceptible trees are to these potential problems.
Act now to avoid damage on nectarines, plums
Do you have nectarines or plums in your home orchard? Are they in bloom or nearly blooming now? If so, and you’ve had problems with scarred or deformed fruit in the past, you may need to take steps to protect the fruitlets from thrips damage.
Thrips are tiny insects that feed inside the flowers lasting from early bloom until the petals drop. The damage from their feeding becomes noticeable on the smooth skins of plums and nectarines as the fruits enlarge. An example of this damage is included in today’s photos.
Nectarines are blooming or about to bloom now, and there is something you can do protect your nectarines from thrips damage. A single application with a product that contains the organic ingredient Spinosad will provide the protection your nectarines need. Apply the spray sometime between full bloom to just after bloom. Thorough coverage is important.
Spinosad can harm bees when it is wet but is safe for bees once dry. Apply your spray in the late evening when bees aren’t active so that the product has all night to dry.
