With all of the rain that we’ve gotten this year, it’s no surprise that fungi diseases are on the rise. And the damp, overcast conditions from this last week aren’t helping the matter.
Fungal spores are dispersed by the wind and can grow anywhere that is damp, cool and shady. Unfortunately for our plants, by the time we notice a fungal infection, it is too late to do much for the plant this year. On the bright side, though, most fungal pathogens mostly affect the aesthetic of the plant and, depending on the severity, won’t kill the plant.
Within the last few weeks, I’ve had several questions about spots on pear trees. Most of these are a disease called rust. If you’ve heard of or seen cedar-apple rust, it is similar. Rust diseases often are recognizable because of their bright orange or red spots, and the growth that occurs on the bottom of the leaves on plants in the Rose family, including apple, pear, quince, peach and plum.
The spots also can appear on the fruit itself. Rust can appear on juniper trees as galls or orange blobs on stems. If you have seen the orange tentacles on eastern red-cedars after the rain in the spring, those are a result of cedar-apple rust. Rust could cause early leaf drop on trees.
These rust fungi diseases are unique in that they require more than one host plant to complete their life cycle. The spores from the galls on an already infected cedar or juniper tree spread to the opposite host, a member of the rose family. These spores can spread up to a couple miles, so just because you do not have a cedar or juniper does not mean that your tree is safe. The fungal spores can infect the leaves and the fruit. And if the fruit and leaves are wet, they can be infected. As the spores progress throughout the summer, the bottom of the leaves will form growths. These growths will produce new spores that will then infect juniper and cedar trees, forming the galls.
The best way to prevent your tree from getting rust is to plant a variety that is resistant to the disease. This does not mean that it won’t get the disease, but it does mean it has a higher chance of fighting off the disease than a non-resistant cultivar, similar to how someone with a stronger immune system has a less likely chance to get the flu.
If you do have cedar or juniper trees and a rose family plant like apple or pear that consistently gets rust every year, you could consider removal of the cedar and juniper trees. If you don’t want to remove them, inspecting them for galls during the winter and early spring and then removing the gall also will reduce the amount of spores that are released.
Pruning infected branches on a rose family tree is helpful for control. When the infected leaves drop in the fall, be sure to remove them from the area as they still can provide a source of infection the next year. As always, chemical control should be the last option for control of the disease. For rust, the fungicide should be applied before the symptoms appear in order to be effective.
Rust may not be pretty, but as long as there isn’t heavy leaf loss, it doesn’t affect tree health significantly. This year has been damp, so fungi are just something that we have to deal with. But removing the sources of infections from the environment and planting resistant trees is a step in the right direction. If you have any questions please contact me at the Buffalo County Extension Office, 308-236-1235, or at mearnest2@unl.