I was asked a question this week by a concerned homeowner whose ash trees are losing many of their leaves. Since there are so many homes with ash trees, I thought I would share with everyone why this may be happening all around this area, though I highly recommend you consult a professional arborist for any specific situations.
First of all, there are a variety of ash trees, so it is important to know which species you have. You may take a picture on your phone of the leaves and bark, or take a sample to a knowledgeable nurseryman, or do a web search and determine the species yourself.
Certain species, like the Arizona Ash, are not particularly good to have in Central Texas. Compared to the Texas Ash, the Arizona is more susceptible to borer insects; it has a weaker structure and can develop diseases more readily. It can also drop more “trash” on your yard than the Texas Ash. Also, the Arizona doesn’t quite fit the hardiness zone here, so there could be a soil and/or a climate issue. Since the Arizona Ash needs a consistent water source and we recently went through a continuous drought for four years or so, it could be leaves are falling as a residual effect from drought.
Local species, Green and White Ash trees, may also contract a fungal disease called anthracnose. Because this area had so much rain this spring, these trees may have contracted the fungus during the new leaf budding period. Now that you may be seeing the leaf drop as a delayed symptom, it’s actually too late to treat the fungus. It won’t kill the tree and you may even see new leaves appear in the next month or so.
Regardless of which species you have, most arborists would probably recommend deep-watering your ash trees, as the sun and heat have stressed them and they probably could use the water. Remember, deep watering is not using the sprinkler system. It is using a hose or manual sprinkler, on low for hours to soak the soil underneath the grass roots. This watering should be done all around the tree to the drip line, not at the trunk. Do this a couple times a month unless we get substantial rainfall. And another quick reminder, mulching the base of the tree helps to hold in moisture and protect the soil from sunlight and hot wind.
Even if your ash trees do not have the fungus, trees can drop leaves simply because it cannot support all the leaves it formed when we had the abundant rains this spring. Now that we are in the 100s for temperature highs, it really stresses a tree to try and keep water moving to support all of its foliage.
Leaf drop during this time of year isn’t a catastrophe, nor is it rare. Trees are tough and capable of responding in such a way as to stay as healthy as possible. These latest leaf drops should not have long-term effects on the overall health of your ash trees.