Monday, May 24, 2010

Hawthorn Cedar Rust

It’s bloom time for the Dwarf Hawthorn, Crataegus uniflora, so I made a point of getting out to look at it yesterday. There were several blooms along with some unopened buds and developing fruit.

The plants looked in good shape. The leaves were a dark glossy green and there was very little dead wood in the plants. Dwarf Hawthorn is rare in Ohio, so I monitor it closely through the year.

I saw a bud with some yellow bumps and since the yellow spots were being tended by an ant, thought they were probably yellow aphids. A closer examination proved that assumption to be false. The yellow bumps were a deformity on the plant itself.

A second bud showed the same spotting. At this point I suspected the plants were displaying signs of Hawthorn Cedar Rust, a fungus with a life cycle like the Apple Cedar Rust I talked about a few weeks ago. However, HCR is most commonly found on the stems and leaves and those looked fine.

Well, maybe they’re not as fine as I first thought. Here are some signs on the stem and the leaves are showing just a hint of spotting. The yellow eruptions are the site of spore release for the fungus. There must also be something present that is of value to the ants.

Here’s a leaf showing development of the fungus galls. Other species of Hawthorn at Blue Jay Barrens display signs of the fungus every year and manage to survive and grow. It’s extremely disappointing to have such a rare plant infected with the disease. Maybe it’s the unusually wet spring that is to blame for this infection and things will get back to normal the next dry year. I’ll just have to watch and see what happens.


  1. Put on that detective's hat!! You'll just have to be patient for next year. Don't you hate that? We have hawthorns here, but not dwarf. They are sweet little plants, aren't they? ~karen

  2. Karen - They're wonderful little plants. Sort of like natural bonsai. They seem to have a die-back pattern that keeps them always at the same size. It seems I'm always waiting until next year for something or other.

  3. Sorry about the problem your having with this fungus!! I have a Hawthorn tree or bush growing on my property some call it a thornapple....would that be in the same has flowers that look like yours!!

  4. grammie g - It should be related to what I have. Most of the species have long thorns on the branches. The flowers look about the same on all of them.