“I Can See Clearly Now – the Rain Has Gone”
Written by: Certified Master Arborist, Tony Arnoldi
Well, maybe not all the rain has gone, but it as a great deal better than last year so far. This does matter for what lies ahead. If a “more normal” pattern of rainfall awaits us, it will begin to reduce the disease pressure that has buffeted our trees for the last 5 or 6 years.
Frequent rains in spring and summer wet the foliage or needles repeatedly. This allows the fungal spores of numerous diseases being carried in the air, which are “windborne” for significant distances, to land on these wet leaves and needles. Once stuck to them, the spores germinate and grow into ever-enlarging fungus material (spots or threads) that can infect the leaves and begin feeding parasitically on them. The following diseases all operate in this general fashion:
- Needlecasts – of spruces, pines, and firs have greatly diminished the beauty and health of so many evergreens that treating for them has grown to be our number one category of care. Treatment is effective but must continue for several uninterrupted years to regain health and beauty.
- Tip Blights – such as Diplodia also work against evergreens to wreck their looks and function. These start by infecting newly emerging needle growth and progress further into the branch over time, browning and killing more of the branch as it does this.
- Anthracnose – causes the formation of brown dead lesions on the leaves of many kinds of trees and shrubs. Many of the infected leaves drop off in summer.
- Leaf spot diseases – like Apple Scab and Rust cause significant leaf infection and leaf drop to Crabapples, Pear, Serviceberries and Hawthorns.
We cannot discuss fungal tree problems without including Root Rots. These opportunistic fungi have caused diminished root systems of many kinds of trees. Decline follows and branch dieback often is a result. Trees with this infection are weakened and often contract other insect or disease issues. Successive wet springs have increased the number and severity of cases and caused many to become deep-seated, requiring multiple-year treatment protocols.
Another type of disease that has exploded due to successive wet years is Fireblight. Fruiting and ornamental fruit trees are attacked by this bacterial disease that spreads easily once infection has started. This disease has gone from a somewhat infrequent disease to a common tree killer. It starts by infecting flowers and branch tips and progresses to more and larger branches.
These and other diseases have done extremely well and have caused many trees to require treatment. Treatment usually helps trees recover slowly over several years as health, beauty, and strength return. Then treatment is done to deter the disease from returning. Treatment protocols should not end abruptly because disease inoculum (spores) remain at a high level. However, if the break in wet years continues, there is real hope that fewer trees will need to start treatment and many trees could reduce or be taken off selected treatments. This is where your Wachtel Tree Science Certified Arborist can help to assess tree and site conditions and manage your tree landscape for the best results.