Plum tree help

Asked October 8, 2016, 7:38 PM EDT

Hi, We have some plum trees that are seeping some sort of sap and turning black on the rootstock portion of the trunk. I attached a picture. There is a flexible film over soft, squishy liquid that started off golden brown this spring, and by now is turning black. The trees were transplanted in their current location about a year and a half ago. Do you have any ideas on what might be going on and what we should do about it? Thank you so much! -Joey

Benton County Oregon fruit trees plum tree horticulture

1 Response

There are several reasons that can cause your trees to ooze sap. Some of the causes are mechanical (lawn mower or weeding), various animals (voles, gophers, etc.), boring insects, bacteria, and fungus. The oozing of sap is normal for a tree that has 'damage', whatever the cause. The tree is trying to heal and protect itself.

The damage on the tree pictured seems to be directly related to its graft. If the oozing sap on your other trees are also at the graft line, there may be a problem or weakness in the graft itself. There is not much you can do about the graft other than taking care of your tree and hope it is successful in healing itself. Things you can do to help your trees is clean up the area under the drip line (the area from the tree trunk extending out to the tip of each limb) of your tree, keeping it weed free. You should also clear the mulch, at least 6 inches, away from the tree’s trunk (voles and other rodents will hide in the mulch while dining on your tree); you can also spray your tree with a fungicide; if you see insects, or insect waste in the sap, use an insecticide spray. There are organic and non-organic sprays available from the larger nurseries in our area. In early Spring I recommend that you fertilize your trees. Make sure that when pruning your plum trees, you do so after the leaves fall and when it is dry.

Here is an Oregon State Extension paper on a cause of ‘oozing sap’ in cherry trees (plums are in the same family (Prunus) with cherries). I hope you find this paper helpful.

https://pnwhandbooks.org/plantdisease/host-disease/cherry-prunus-spp-bacterial-canker

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