While that week of rainy weather was good for all the plants we are trying to grow, it’s going to create some issues with tree leaves down the road. Not fatal issues for trees, but issues that we see every year when we have a wet spell in spring. While the following items are not going to be all inclusive, it will hit a bunch of the problems.
There are numerous minor leaf diseases that can cause problems after a week of wet weather. Maple and elm trees can get various leaf spots from anthracnose or taphrina leaf blister that may knock a fair number of leaves off. Most of the time, the small spots on the leaves will be easily enough to see. The leaves often turn yellow and come fluttering off a few weeks down the road. Ash trees are likely to exhibit swelling and distortion on the leaves from ash rust. Once the symptoms of the disease are evident, it is far too late to treat, but the damage these diseases do is so minimal that other than being a bit of a nuisance, it’s nothing to worry about.
Sycamore trees were just really leafing out when that rainy weather hit. Sycamore trees are very susceptible to a disease known as sycamore anthracnose. All those little leaves that were starting to grow during that period are likely to turn brown or black and fall off. Anthracnose also often causes small branch tips to die back. As new leaves start to come out, new branch growth will begin from a bud that is still alive. While unsightly and concerning, the tree will leaf back out and it will be fine.
Do not let someone talk you into spraying the tree at that time as it is too late. While a treatment before the rainy weather would have helped, the expense of that treatment can likely not be justified. The regular die back of branch tips give sycamore tree branches a very unique zig-zag appearance which I feel gives the trees a lot of character!
During that rainy week, the cedar trees sprouted all sorts of tan and orange funny looking growths. Some of the growths looked like orange jellyfish, while other growths looked like light tan mucus dripping off the branches. These were examples of some of the different rust diseases that infect cedar trees and then other trees, virtually all being in the rose family. The three diseases are cedar-apple rust, hawthorn rust and quince rust. The appearance of these three diseases on cedar trees is noticeably different, but it really isn’t important to know which is which. Cedars simply serve as the alternate host. The damage they do to cedar trees is pretty minor. It’s the damage they do to the main host that is of concern.
As their names imply, these diseases also live on apple, pear, quince and hawthorn trees. We don’t have a lot of quince trees (just shrubs) and slightly more hawthorn trees. We have a lot of apple trees though. Apple trees, both fruit apples and flowering crabapples, have varying resistance to this disease. Some apples, like red delicious, are quite resistant to the rust diseases. Others, like Jonathon and golden delicious, are quite susceptible to the rust diseases. If an apple tree is susceptible, it will soon start to develop yellow spots on the leaves that will grow, die in the center and then fall off. Spores from these infected leaves will move back to the cedar trees this fall. Since there is just one infection period per year (spring), the trees will re-leaf.
To prevent susceptible apple trees from developing the disease, we normally need to spray fungicides every seven to 10 days from late April through the first of June. If your tree is defoliated this year, plan to start treating it after it blooms next year. If the leaves continue to develop black spots and fall off through the summer, then we are dealing with another disease known as apple scab. Which is a disease story for another day!
CHUCK OTTE is the agricultural and natural resources agent with the Geary County Extension Office.
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