Colorful rust diseases often lead to significant leaf browning. The host tree shown here was labelled as LaValle hawthorn. Many rusts require two hosts to complete their lifecycle. "Cedar-apple rust" and related rusts require juniper or eastern redcedar trees as an alternate host.
More educational pictures of this rust fungus. Note: the last picture may make some folks a little squeamish....
Here is the whole hawthorn leaf with the rust spots. Not sure if this is the image I used to make the banner.
Next is the rust fungus as it appears on juniper. This is called a gall.
Finally, in the spring when there is rainy weather, these galls sporulate and produce these orange gelatinous fingers which will produce the fungal spores that infect the apple, hawthorn, pear, or whatever the alternate host is.
Super job grabbing our attention with a visually striking banner, and adding to our education with the additional photos. I managed to guess the leaf shown had some sort of disease, but that's as far as I got. I'd never seen the disease stage shown in the third of your photos, but junipers and apples and hawthorns are common enough that I should make a point of looking for it this spring.
Is there a forum on this site for talking about, and illustrating plant diseases like this? If not, there should be.
Thank you, all for the likes, acorns, comments and links! Plant diseases can sometimes be quite interesting despite the fact that we fight with them in our quest for a beautiful and bountiful garden.
Name: Cal McGaugh Escondido, California (Zone 10b)
My first reaction was like Dirt's....."Yikes!"
Rust is my nemesis, especially for my hollyhocks.
But I found that if I give them Bayer 4-in-One early
before it is visible, they get very green & buff, and
it prevents the rust.
Thanks, though for the all the info, pics, & links by Baja, et al.
which will produce the fungal spores that infect the apple, hawthorn, pear, or whatever the alternate host is.
Very interesting and educational, Laurie.
