Plum Tree has Fireblight? I Don't Think So.

Q. I'm hoping you can help save my plum tree. It has fireblight, I cut off the infected area but it spreading to the rest of the tree. It has these gel filled sacs that are moving through the tree and not sure how to treat it. Can I save the tree?

Early summer growth with fireblight. Happens around May in Las Vegas and is only in Asian Pear, European Pear, Apple and some ornamentals in the rose family of plants.

A. It is not a disease such as fireblight. That disease only attacks European pear, Asian pear, and apple as far as fruit trees go. Not plums. It will damage some ornamentals in the Rose family of plants. Damage from fireblight is seen starting in about May. Your “gel filled sacs” are typical of plum when limbs over half inch in diameter are damaged from anything; diseases, natural causes, or insects. Damage this time of year usually comes from the sun (sunburn) or from boring insects or both.

Sap oozing on plum trunk and limbs can make you think of fireblight, but it can't be.

“Sunburn” damage can be a two-edged sword; it can cause damage on its own, but it can also lead to further damage by boring insects that we refer to as “borers”. Borers in our climate are beetles with an immature form (grub) which tunnels into damaged stems. The kind here are never found in the ground. Frequently these stems may first be damaged by intense sunlight (sunburn). If this damage is caught early enough (March through June) and it is light, any grubs can be easily pruned or cut out with a sanitized hand pruner or knife. If left to do their tunneling until later in the season (June through September) or if the attack is severe, the only treatable option is chemical control using a soil drench of an insecticide. Looks like you are left using a soil drench.

These pockets of sap coming from the trunk and limbs, accompanied by dieback, are positive indicators of borers. By this time of year and when you see dieback, borer damage is in an advanced stage. Find the Bayer insecticide for borers in fruit trees and apply it as a soil drench around the tree following the label directions.

An irrigation moves this poison inside the tree from the roots. This soil drench treatment allows the “poison” to move throughout the entire tree. You cannot eat any fruit from this tree the following year. The parts of the tree that are dead will not come alive but hopefully you will see some new growth from the trunk or limbs after about a month. You will know if you are successful or not by October.