PHC Curveball: Fungus Weather
Written by: Anthony Arnoldi, Board Certified Master Arborist #WI-0102B
Posted: 2024 | Disease Treatment | Insect Control | Summer | Tree and Shrub Care
We’ve had it again: the kind of weather that breaks records. Three years ago, we had a record-breaking wet spring; this spring has broken that record. Wet weather has dominated the first half of the 2024 growing season. Evidence of thriving fungi is everywhere to be seen.
We all know that familiar fungi like mold and mildew do best in cool, moist environments; it is the same with the fungi that attack trees. We are seeing fungi cause visible damage to many species of trees.
Many fungi form leafspots or lesions on the leaves of deciduous trees. These lesions begin too small to be seen, when spores land on wet or moist leaves in spring. Over time, the spots grow larger as fungus feeds on the leaf tissue as a parasite. Eventually, the leaf may fall off with accumulated damage. Examples of leafspot diseases this spring include:
anthracnose on ash, oak, maples, sycamore, and other species;
tar spot fungi on maple leaves;
apple scab on crabapples;
and rust on hawthorns.
Not all leafspot diseases require action. However, if many leaves fall early in consecutive years, treatment may be needed, as is the case with apple scab and rust.
The weather this year has enabled fungi like apple scab to have an extremely long infection time, and even sprayed trees are dropping leaves. This year’s crabapple leaves were “born” with apple scab, and those first leaves produced have begun to fall off. Treatment still enables many more leaves to be retained until fall so that food can be made, and some aesthetics can be preserved for the
year. More importantly, treatments prevent scab disease from becoming a serious health concern.
Other fungi form leafspots on evergreen needles. These are called needlecasts and cause browning and needle loss on spruce and pine. With heavy infections, these fungi can reduce both beauty and health of affected trees; they must be more routinely controlled. Needlecasts have steadily increased their infection rate over the years, and we have had to treat many evergreens! Spruce trees especially have been struggling with alternating needlecast (Rhizosphaera) and drought for years, and many really show this wear. Experience has shown that patience is needed to preserve spruces: many trees that have had consistent and uninterrupted care for several years have been able to prevail and to slowly restore replacement needles. Trees may not regain all their prior density, but they can still provide much needed evergreen accent to landscapes.
Yet another important group of fungi are known as root rots, or root collar rots. These attack the root system and lower trunk. They also have increased over the years as trees weakened by previous years of drought encounter wet soils. Again, these diseases benefit from the alternating too-dry, then too-wet soils. Sudden tree death is often attributable to these fungi.
Fungus issues are generally more challenging to control than insect outbreaks, so remaining proactive and providing consistent care are necessary for success. You can count on Wachtel Tree Science to provide the best, most up-to-date care for every situation. Call your ISA Certified Arborist to have your trees assessed, and to determine the best management plan to safeguard the health of your trees.
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