Every year we get numerous calls asking why a tree’s leaves or needles are yellowing and falling in abundance at seemingly odd times. There are a variety of reasons for tree stress, which are discussed at length in other pages on our website. Please visit Apple Scab Disease, Anthracnose Fungus, Early Fall Color and Iron Chlorosis.
Sometimes, however, early leaf drop or needles falling may just be a natural occurrence. Here are just a few examples of leaf/needle drop that affect certain species of trees.
If your River Birch looked really thick and full in the spring, but once the summer heat arrived the area around the tree became littered with fallen, yellow leaves, there could be multiple reasons for this occurrence.
It is fairly common for River Birch leaves to turn yellow due to Iron Chlorosis, caused in large part by poor soil conditions. Chlorosis is distinguishable from ‘natural’ shedding by the fact that the veins of the leaf will stay green, but the tissue in between will turn yellow.
When soil moisture begins to dissipate, the tree realizes that it does not have enough moisture to sustain that full crop of leaves it originally produced. The tree will then shed a lot of its interior growth to protect itself during the heat of summer.
Crabapples, which are susceptible to Apple Scab Fungus, lose leaves all summer long due to this disease. When a Crabapple tree has Apple Scab Disease, it generally loses 50% to 90% of its leaves throughout the summer. However, when we treat a Crabapple tree it will retain 95% of its leaves.
Clients get nervous when the leaves of trees that we are treating for Apples Scab begin to yellow and fall. It’s understandable that they think the spray applications may not be working. Rest assured this is not the case! The main reason for this leaf loss is that the Crabapples that we treat are so thick and full of leaves (which they have not experienced in years prior to our treatments) that the inner leaves on the tree no longer receive the sunlight they require due to the now thick canopy, so they yellow and drop.
Scotch, Austrian and especially White Pine
Inner needle shedding is a normal process, even on the healthiest of pines. When we look at the inner areas of any mature conifer, evergreen or pine tree, there is no live, green growth in there. This is because pine trees only allow themselves 5-7 years of growth before they naturally shed their inner needles.
As the tree keeps pushing out new growth year after year, the inner areas become more and more shaded. The needles yellow and drop due to the sunlight’s inability to reach them. This situation may occur to a minor extent on a yearly basis, but then, every 3-4 years, the dieback may seem excessive.
This looks scarier than it is, although do not completely discount the possibility that the situation could be due to a combination of other factors such as Borers, Sphaeropsis Fungus or poor soil conditions,
Professional Root Fertilization is the best way to ensure the health of urban trees and to protect them from the stresses they endure.