Sunday, August 15, 2010

Hawthorn Cedar Rust - Follow-up

A few months ago I mentioned the Hawthorn Cedar Rust that was attacking the Dwarf Hawthorn, Crataegus uniflora. The rust has been very detrimental to many of the hawthorn fruits. Fruiting bodies have recently opened and deposited spores onto the leaf below. Fortunately for the hawthorn, these spores are only capable of infecting Eastern Red Cedar, the alternate host in the rust life cycle.

Leaves have also suffered from the attack of the rust. Brown patches and edges are the most evident results.

Twigs that showed rust damage in May have developed these hard growths. This is a rather odd looking growth and looks as though the plant was trying to defend itself by growing a woody barrier between itself and the rust. As a defense against fungal invaders, many plants will use this type of defense and the result is a canker or odd growth mass at the point of infection. Maybe I don’t have to be so worried about the Cedar Rust killing off these uncommon plants.

As a whole, the shrubs look healthy. Fruit production was low this year, but the plant itself doesn’t seem to have suffered.

A few small yellow spots are all that is left of the infection on most of the leaves.

There were even several healthy fruits produced. My visit to the Dwarf Hawthorns had me in a really good mood. That changed slightly when I pulled my arm back a little bit too far while taking this shot.

I felt leaves brushing the back of my arm and then there were a couple of pin pricks. At first I thought it was just those pesky ants trying to protect some food source they had found on the hawthorn leaves. I ignored it and went on with my picture taking, until a wash of hot prickles started to spread from my elbow to my shoulder. I had managed push against this innocent looking mass of fluff, commonly known as a Flannel Moth larva. Beneath the fluff is a collection of poisoned spines that produces an effect similar to stinging nettles. As I type this, about 12 hours after the encounter, my arm is still sore and I have a nice red welt. At least I now know how I react to this particular poison. It probably wouldn’t have been this bad if I’d had the sense to pull away at the first sting.


  1. Hi sure can get yourself in a pickle can't you....I know what it fells like to it into nettle but never heard of this stuff!!
    Interesting stuff how the plant protects it self...I have seen growths like that before but never would have thought that that could be the cause!!
    Have a great day!!

  2. I had no idea that innocent looking fluff on the moth caterpillars had that defense. Glad your hawthorne plants seem to be taking the rust infection in stride. Are there many eastern red cedars around? If this is similar to cedar apple rust, the fruiting bodies on the cedar in the spring look really cool. Hope your arm feels better.

  3. grammie g - I've been getting into messes most of my life, but I'm pretty good at getting myself back out. I've suffered the wrath of all manner of plants and animals. Aside from a few scars and some interesting memories, I've managed to survive all without any negative effects.

    Wilma - Eastern Red Cedar is one of the most common trees in this area. Back in May I posted pictures of the Apple Cedar Rust Gall. The Hawthorn Cedar Rust Gall is very similar.