Sap from plum tree - Ask Extension
Sap is dripping from this plum tree. There are dark purple bumps/blisters on branches. Tree looks fine other than sap issue. Tree has never done this ...
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Sap from plum tree #834481
Asked June 08, 2023, 6:28 AM EDT
Sap is dripping from this plum tree. There are dark purple bumps/blisters on branches. Tree looks fine other than sap issue. Tree has never done this before. Noticed it a couple weeks ago. Had people look at it. No one has ever seen this before. Thanks for your help. Will include pictures. Last picture is from a branch that was pruned and removed.
Macomb County Michigan
Expert Response
Hi Brian,
This looks like the lecanium scale insect. The sap is caused by the crawler stage feeding on the plant's sap, which causes them to release a sticky substance as waste. It's called "honeydew", and a black sooty mold will grow on the sugary substance.
https://www.michigangardener.com/identifying-and-controlling-lecanium-scale/
Look under the leaves for tiny, tiny, green insects feeding, especially along the veins of the leaves.
Most trees and shrubs are not harmed by the insect feeding. And natural predators are likely gobbling up the insects each day.
If you feel control is warranted, there are options listed at the end of the article at the link above. Keep in mind that a systemic root drench of imidacloprid may persist for a couple of years, making all parts of the plant poison to the scale insect as well as pollinators.
Roscommon, where I'm based, experienced an outbreak of these scales on oak trees in 2016. In most cases, people did nothing about it due to the size of the affected trees. The insects were a problem for 1-2 growing seasons, then natural predators caused the population to collapse without the need for chemical control.
If you have any questions, or wish to discuss, please feel free to reach out.
Thank you,
-Julie
This looks like the lecanium scale insect. The sap is caused by the crawler stage feeding on the plant's sap, which causes them to release a sticky substance as waste. It's called "honeydew", and a black sooty mold will grow on the sugary substance.
https://www.michigangardener.com/identifying-and-controlling-lecanium-scale/
Look under the leaves for tiny, tiny, green insects feeding, especially along the veins of the leaves.
Most trees and shrubs are not harmed by the insect feeding. And natural predators are likely gobbling up the insects each day.
If you feel control is warranted, there are options listed at the end of the article at the link above. Keep in mind that a systemic root drench of imidacloprid may persist for a couple of years, making all parts of the plant poison to the scale insect as well as pollinators.
Roscommon, where I'm based, experienced an outbreak of these scales on oak trees in 2016. In most cases, people did nothing about it due to the size of the affected trees. The insects were a problem for 1-2 growing seasons, then natural predators caused the population to collapse without the need for chemical control.
If you have any questions, or wish to discuss, please feel free to reach out.
Thank you,
-Julie
