The hawthorn trees at my rental property are diseased. Can you look at the pictures and tell me what the disease is and what I should do to save them? Thank you - Ask Extension
The Hawthorne trees at my rental property are diseased. Can you please look at the pictures and tell me what the disease is and what I can do to save ...
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The hawthorn trees at my rental property are diseased. Can you look at the pictures and tell me what the disease is and what I should do to save them? Thank you #868319
Asked May 13, 2024, 11:01 PM EDT
The Hawthorne trees at my rental property are diseased. Can you please look at the pictures and tell me what the disease is and what I can do to save them? Thank you.
Larimer County Colorado
Expert Response
The hawthorn tree’s lower branches are black and dead. There is white splotches on the trees. Please refer to my attached pictures.
Hi Catherine,
This is likely hawthorn mealybug - they overwinter in the bark and cracks of trees and then migrate onto the branches during the summer. While common, this is a pretty heavy infestation and treatment should be considered.
It's a difficult insect to control because of its waxy coating, but you can try using horticultural oils now (before the end of May). You can purchase this at a garden center. It wouldn't be a "dormant oil" but perhaps one that is a bit lighter ("summer weight"). You'll spray it on the trunk to evenly coat the insects.
An alternative would be to use systemic insecticides, but I would wait to apply these until after the tree blooms (which is usually in June) so you don't affect pollinators.
You can prune the dead branches (those that don't leaf out) from the canopy.
This fall, do another horticultural oil application, targeting the insects on the branches.
Here's a good publication about the biology of the insect and control options: https://webdoc.agsci.colostate.edu/bspm/Hexapoda%20(Insects)/Hawthorn%20Mealybug%20December%202014%20Revision.pdf
This is likely hawthorn mealybug - they overwinter in the bark and cracks of trees and then migrate onto the branches during the summer. While common, this is a pretty heavy infestation and treatment should be considered.
It's a difficult insect to control because of its waxy coating, but you can try using horticultural oils now (before the end of May). You can purchase this at a garden center. It wouldn't be a "dormant oil" but perhaps one that is a bit lighter ("summer weight"). You'll spray it on the trunk to evenly coat the insects.
An alternative would be to use systemic insecticides, but I would wait to apply these until after the tree blooms (which is usually in June) so you don't affect pollinators.
You can prune the dead branches (those that don't leaf out) from the canopy.
This fall, do another horticultural oil application, targeting the insects on the branches.
Here's a good publication about the biology of the insect and control options: https://webdoc.agsci.colostate.edu/bspm/Hexapoda%20(Insects)/Hawthorn%20Mealybug%20December%202014%20Revision.pdf
