Garden Word of the Day
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Shade Tree Decline
Shade tree decline, or shade tree disorder, is a term used to describe branch and twig dieback in the crown of a tree. These trees are not affected by pests or disease, per se, but they are sick.
In winter, most deciduous trees are bare. By late spring, a thick blanket of sugar-producing machinery covers those trees. Every leaf surface should be cranking out energy as fast as it can. In recent years, especially in heavily populated areas, somewhat healthy-looking trees tend to be a bit thin on top. This thinning is not a hormonal problem treatable with hair tonic. Shade tree decline is a serious problem. Those trees are dying.
Drought (or lack of proper irrigation) is the number one cause of shade tree decline, but there are other causes. And ornamental trees are not the only victims. Canada’s sugar maple trees have been exhibiting shade tree decline for decades. That decline is due to air pollution blowing northward along our Eastern seaboard. [My sincere apologies, Canada.] There are many other causes (and few solutions) to the problem of shade tree decline.
Symptoms of shade tree decline
Symptoms of shade tree decline appear gradually. Like the frog in the proverbial pot, we often don’t notice the damage until it is severe. Initial signs of shade tree decline include:
Later symptoms include:
These are all signs that the tree knows it is dying. It is frantically putting what little energy it has left into the next generation. Most trees affected by shade tree decline die within a few years.
What causes shade tree decline?
Imagine being pummeled all day, every day. Professional boxers do it, but they have strict nutritional support, medical teams, and proper hydration. Drought, pollution, and injuries have plagued our trees for many years, but most never noticed. Some of the more common injuries include the following:
The downside of shade tree decline
Trees are an investment in the future. They cost money and take time to grow. They also prevent erosion, provide shade and food, store carbon, create the oxygen we breathe, and filter pollutants out of the air. They provide habitat and food for many other living things, promoting biodiversity. As a tree begins to suffer shade tree decline, it becomes less able to defend itself against pests and diseases, becoming more likely to suffer sunburn damage, providing easy entry to borers and other insect pests.
The bigger problem
The Carnegie Institute for Science reported that California lost more than 58 million large trees between 2011 and 2015. Even when heavy rains appear, the damage has already occurred, and tens of millions more trees will die. The strain on the trees has been too much. Dead and dying trees harbor pests and diseases in epidemic proportions. The large-scale die-off of trees also makes it easier for invasive plants to get established. And sick trees can be fire hazards.
Preventing shade tree decline
Prevention is much easier and more likely to succeed than treatment. You can help your trees stay healthy by recreating the conditions they evolved in to prevent shade tree decline.
These tips can help you protect your trees against shade tree decline:
Treating shade tree decline
Prospects for an affected tree are not good. The damage has already occurred. Even the most diligent care may not be enough. If you are determined to try, these actions may save your tree or help it to survive a little longer:
How to irrigate trees
Most tree roots are in the top 12 to 18 inches of soil. When these roots get too dried out for too long, they die. Fewer roots reduce the amount of water available to the tree for life processes and cooling (and growing new roots). Frequent, light watering encourages shallow root development. Deeper roots are less likely to be damaged by the elements and may access groundwater.
Properly irrigating trees means getting the water to a depth of at least five to seven inches every three or four days during the peak of summer. Before we knew better, we used to plant trees in bowl-shaped depressions we would fill with water. Sounds good, but it’s a bad idea. This practice leads to crown rot and several other fungal diseases. Better methods include soaker hoses and irrigation rings. Irrigation rings can be mechanical devices or nothing more than trenches dug around trees at the drip line. Fill the irrigation trench with water every few days during the peak of summer, and your trees will thank you.
Selecting the right trees
If it is too late to save your tree, invest in a reputable arborist for professional removal. Trees can be deadly. Seriously. Then, use the following information to select trees better suited to your microclimate:
Fighting Mother Nature is a full-time job, and it’s mostly a waste of time. Rather than setting ourselves up for tons of maintenance in a never-ending battle, put the things that occur naturally in your landscape to work for you and your trees.
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