Do your peach trees have some gummy looking sap exuding from the trunk? Gummosis is the term for the symptom of gummy sap oozing from the trunk and branches. It is not that unusual and can have several causes. Chemical, physical, insect, disease, or stress damage to the trunk can cause this symptom. Before you worry too much about it, you need to rule out the most destructive causes.
There are two different peach borers that bore into trunks and scaffold branches that can cause this. Make sure there is no bore hole and frass beneath the sap to rule out these problems. The Peach Tree Borer attacks trunks, and the Lesser Peach Tree Borer attacks the major branches. More information on borers.
Too much water on the trunk can cause damage that results in gummosis. Irrigation heads that put water on the trunk and high weeds that hold moisture in around the trunk are culprits. Make sure your irrigation head shoots water around the tree but does not put water on the trunk. Control the weeds around the trunk but do not use glyphosate herbicide. Glyphosate, the common ingredient in Roundup®, is easily absorbed through the thin bark of peaches and can make the problem worse. Water stressed or poorly managed orchards are also at greater risk.
Physical stress to the trees can cause microscopic injury to the wood that results in gummosis. Wind is not kind to peaches, the fruit or the branches and trunks. Hurricane Irma shook a lot of trees around and they are showing the symptoms now. However, if the trees are growing well and you have eliminated other stresses, this does not mean the loss of your tree. Correct any problems that can lead to fungal infection and a worsening of the problem.
Botryosphaeria is a fungus that can enter wounds or even the lenticels on peaches. Trees that have damage from all the above mentioned problems can also become infected with this fungus, making the problem much worse. This fungus causes raised blisters at infected lenticels leading to necrotic cankers that ooze sap in the second year. Large cankers will coalesce, killing branches or the entire tree. More information on fungal gummosis.
Reduce stress and practice sanitation by removing and destroying diseased wood. Avoid pruning immediately before or after a rain or irrigation event when leaves are wet. Avoid pruning water- and nutrient- stressed trees. Prune trees with gummosis last. Clean pruning tools after pruning an infected tree with mild bleach, rubbing alcohol, or quaternary ammonium solution to sanitize tools. Fungicide applications to the trunks of young trees may help to suppress fungal infections. The latest fungicide recommendations.