Other than, "How tall are you?, " the question I get asked most is, "What is a plant pathologist?".
I guess that "plant pathologist" conjures up images of a person in a white lab coat dissecting a dead plant on a cold, metal table. A forensic pathologist....only for trees.
Most of the time, I'm not playing the role of a coroner (sometimes, though!) but rather studying the diseases and insects that interact with and affect the health of landscape plants. As a field plant pathologist, most of my time is spent at nurseries or in landscapes looking for signs and symptoms of fungi, bacteria, viruses and insects.
It is a lot like CSI most of the time. I have to asked a lot of questions to find out what happened prior to illness. How often was it watered? When was the last time it was fertilized? When did you notice it was in decline? Have you done anything to this plant recently?
A few weeks ago, I started seeing this on the Camellias at a few nurseries and in gardens:I had been told a few years ago by another pathologist that it was a virus called Camellia Ringspot Virus. Although the leaf spots look very viral, something about it didn't add up (you have to go with your gut a lot), so I took a second look when it appeared this winter.
The circular leaf spots occur on older foliage following cold weather. As soon as the new leaves emerge in the spring, these diseased leaves fall to the ground.
As it turns out, this ring-spotting is caused by a fungus. And this fungus overwinters on the infected leaves that fall to the ground beneath the Camellias. After a week or two on the ground, a large brown lesion will develop on the leaf.
If conditions are right, the fungus will sporulate and fruiting bodies will become evident on the leaves. This is an image of the fruiting bodies though a dissecting microscope:The black squiggly stuff is actually masses of spores that are being pushed out of the fruiting bodies. Plant pathologists call these spore tendrils. It's kind of like a really bad pimple.
When you look at these spore tendrils under a microscope the spores are visible.
This is how I am able to diagnose the disease that is affecting a plant- by the spores. Just like a flower is the definitive way to determine the species of a plant, spores are the way you determine the species of a fungus. In this case, Phyllosticta (the asexual phase of Guignardia).
And that's what a plant pathologist does (sort of). Wow, right?
If you are a bit geeky, this article has all the information you'll ever need: A New Leaf Spot Disease of Camellias caused by the Fungus Guignardia.