This is a plant disease topic we usually talk about in a few weeks but with the weather we have been having, it’s likely that rust season will start a little earlier this year. And when we are talking about rust disease, we are talking about a parasitic plant disease, not the type of rust that forms of metal.

Rust disease is pretty interesting in that it is a disease that migrates between two different host plants in one life cycle. Some year’s it seems like rust disease is everywhere but in other years, not so much. So, we’ll just have to wait and see about this year.

Right now, you can find rust disease residing on cedars and junipers, but as the weather warms up, it’s about to jump to another species of plant. In the case of Cedar Apple Rust, it is about to migrate from cedar and junipers trees to apple trees. In the case of Asian pear rust, it is about to migrate to pear trees in both the ornamental and fruit producing varieties.

While Asian pear rust is more challenging to identify on cedars and junipers due to its small size, Cedar Apple Rust on cedars and junipers is about to put on quite a show. During the winter, Cedar Apple Rust can be found in the shape of a mostly round gall. These galls can vary in size from about 1/16^th of an inch in diameter to about two inches in diameter.

When the spring rains come, these galls absorb the rain and begin to push out what are known as telial horns. These horn shaped protrusions are gelatinous, orange, and something you won’t soon forget if you see one. When fully extended, these horn covered galls, can grow to about the size of a baseball.

Your initial defense against Cedar Apple Rust would be to remove these galls if you have them on your cedar or junipers. If the telial horns are starting to appear, you can still remove them, just maybe wear some gloves. These horns are home for the fungal spores that the wind will relocate to another host plant, in this case, some sort apple tree.

Removing all of the galls is a great defense against this disease, however the spores can ride the wind for up to a mile, so you’re not completely out of the woods.

If you have an apple tree, or perhaps a pear tree like a Bradford Pear, you can begin to treat the tree when the leaves start to emerge. To treat, you can spray your trees with an appropriate fungicide through April on a 7 to 10 day interval. Appropriate fungicides would include copper hydroxide, chlorothalonil, myclobutanil, or propiconazole (use as specified on the labels).

Later in June through July you can follow the same treatment program to reduce the incidence of rust disease transferring back to your cedars or junipers. Do this in late June through July.

The good news is that in most cases, rust disease will not be fatal to your plants. However, if your apple or pear tree gets a bad outbreak, you are going to lose a lot of leaves. The tree will grow new leaves, but it can look pretty terrible for a while. Good luck!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701 or by emailing us at mg@tulsamastergardeners.org. Photo: Tom Ingram