Fall 2010-Leaf Spots, Early Fall Colors, Leaf Drop, Oh My!

Fall 2010 Newsletter in Adobe PDF format

By: Anthony Arnoldi, Board-Certified Master Arborist WI-0102B

It has been increasing ever since the middle of summer – trees showing greater and greater amounts of stress as summer has worn on. The number of concerned calls we received inquiring as to the reasons for this have increased right along with these symptoms.

After a dry start that lasted through the end of April, the long-awaited rains came. Once it started, it kept coming regularly, many times with significant storms and rainfall totals, as many people who had flooded basements in Glendale and elsewhere know all too well. The trees certainly benefited from the abundant moisture and grew noticeably more foliage this year. Unfortunately, the fungi that cause leaf spots also loved the extra moisture. As I had written about in an earlier article, “Fungus Weather”, these fungi need repeated leaf-wetting events to get established and then to be able to sustain growth across the leaf surface. This infection creates dead spots of ever-increasing size as the fungus grows (leaf spots). Other fungi cause similar problems of leaves, but look more like irregular brown splotches of dead leaf tissue. Still another group of fungi causes a white film to develop on leaves (“powdery mildew”). This one, in particular, looked quite dramatic on maple leaves and caused quite a stir.

All of these roared along at a record pace until, by mid to late summer, they had caused sufficient damage to make many leaves fall. For some types of trees, such as crabapples showing apple scab defoliation, or hawthorns showing rust defoliation, spray programs are recommended because these fungi cause annual, predictable heavy defoliation that weaken them over time. For most others, however, this year was an anomaly, causing heavy defoliation this year only. Trees can withstand a single year of early defoliation without serious injury. Because of this, spray programs are usually not recommended for the many leaf spot diseases. But be careful: we have learned of at least one case this year where powdery mildew was touted as a deadly disease that would cause their tree to die unless immediate treatments were started! Be sure you can trust your source of information.

This summer was also known for its heat. Along with the moisture, the heat made for an incubator-like environment that helped grow fungi at the accelerated rate. It also was an additional stress on the trees. This helps explain why leaves were dropped even earlier than would have been the case through fungal action alone.

The stresses of the year caused many trees and shrubs to manifest early fall colors. Trees displaying this symptom are surely affected enough to be concerned about. Root rot fungi are often involved in cases like these.

So, what is the take-home message from all of this? First of all, do not panic, nor listen to those who would try to panic you, or try to rush you into fast decisions. Instead, gather all of the relevant facts. Think of how the tree has reacted the last few years. For many trees suffering from a heavy defoliation, it may be a good year to try to relieve stress, and build health. Fall Fertilization, Compost tea, Mycorrhizal root inoculation, and Root Biostimulant therapy can all help do this. There may need to be some detective work to uncover an underlying issue when early fall colors are involved. Always know that you can call your Wachtel Certified Arborist to help sort through all of the information and misinformation, so that you can make a truly informed decision that can help reduce stress, both for you and for your trees. This is our passion.

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