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Why are fall colors muted this year in Centre County?

Fungus attacks a Sugar Maple tree in Centre County.
Fungus attacks a Sugar Maple tree in Centre County. For the CDT

Fall has been my favorite season for more years than I care to count. Fall reminds me of the first day of small game season and the annual trip up to Uncle Mark’s place in Hershey.

In the fields, the corn was drying down and turning brown, fields of beautiful orange pumpkins were prevalent and the local farm stands were filled with the bounty of the fall season. The mountain ridges became alive with hues of reds, yellows, oranges and the temperatures continued to drop along with the humidity of the dog days of summer. Sometimes, I could even catch a whiff of wood smoke in the evening air — a true sign that fall was underway. The wildlife, large and small becomes more active, seeking out and stocking up on food for the coming winter months.

Fall is indeed a beautiful season with all the activity, smells and sights, but this year the colors on the mountain ridges may be muted.

Why would the colors be muted this year? I want you to think back to the kind of weather that we had this past summer. Did we have any rain? What about the humidity? What about the temperature? I know that sometimes I felt like a duck and wanted to see a few sunny days so things could dry out. What about mold growing on wood on your house? My friend who lives in Ocean City, New Jersey, said that he never experience a summer like this past one. It was so humid and damp, which is really unusual for the seashore.

OK, I think we have established that it was wet and humid with cool temperatures this past summer. What about diseases in your garden and on your trees? This is when I started to notice that something just wasn’t right with my trees. I noticed that the leaves were starting to drop like it was fall. I started to notice some spots on the leaves of the maple trees in particular. I began to suspect that I was observing a fungal disease that was attacking the trees. It began to get more pronounced as we entered the fall season.

Fungal spores are most commonly spread by wind-driven rain that reaches leaves less exposed to sun and air. Dead leaves can infect healthy leaves by shedding spores as they fall to the ground. Birds can also move spores if their claws grasp twigs that are harboring spores. You can also carry infected leaves from place to place.

If a tree is taller and isolated, it may seem to avoid the infections because they have better air circulation to keep the surfaces of their leaves dry.

One of the fungus diseases is septoria leaf spot, which isn’t expected to harm the maples because by the time they are infected, the trees are preparing to shut down for winter. Small brown spots rimmed with yellow when the leaves are still green characterize a septoria infection. As the spots grow and merge, they perforate the leaves. Another disease called anthracnose has been afflicting other trees. Anthracnose usually occurs in spring but because there were heavier than usual rains and cool days and nights this summer, the spores that cause it were allowed to germinate in the moisture, leading to an outbreak in mid-August. The tree’s response is to drop its leaves. My Norway maple usually has beautiful yellow leaf colors but this year the tree dropped all its leaves already.

I thought I better double check with Sara R. May, coordinator of the Plant Disease Clinic at Penn State, and see if she has been seeing an uptick in fungus diseases on trees. May sent me an email in response to my inquiry and said that I was right and she has been seeing a lot of fungal leaf spot diseases on trees this year due to the wet weather. May said that usually these leaf spot diseases do not cause enough harm to the tree to warrant using a fungicide.

She recommended that raking and destroying the leaves can be helpful in eliminating some of the overwintering fungus inoculum since many of these fungi survive overwinter on the spotted leaves left on the ground. For high value trees or trees that are stressed due to other factors such as construction, drought stress in past years, insect damage, etc. then folks might want to protect trees with fungicide applications.

I know that my own trees will not have the spectacular colors that they had last year and all I can hope for is that maybe the weather pattern will be a little drier next year.

Bill Lamont is a professor emeritus in the department of plant science at Penn State and can be reached by email at wlamont@psu.edu.
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