Tree diseases can appear suddenly, without warning, and can really surprise us with the amount of damage they can do in a small amount of time.  For 30 years, I have been diagnosing and treating tree diseases. and look at trees at several properties a day during the summer. I could not count how many times property owners have told me "This tree was looking great, until I came out yesterday and noticed that half  the leaves were dying or dead", or something similar to that. Tree diseases are often like that. Halfway through summer, one tree out of many will suddenly start looking sickly,

The question here is, why? Why does one tree fall ill and none of its companions do? The answer is, much like humans, lack of proper nutrients and water. This lowers their resistance to both tree diseases and invasive tree insects. When a tree grows, it distributes a certain percentage of its energy towards growth, and a percentage towards defensive measures, such as toxic compounds which can resist or defeat tree disease or insects. A tree only has so much energy available to it via photosynthesis. It is basically a solar powered pump. It is constantly pumping sugars and water from the roots up to the canopy, and down from the canopy to the roots. When you have a long hot stretch of weather and the tree is not getting the water it needs, it then has to conserve some of its energy to just survive the drought, thus less of its energy goes to generating defensive compounds, leaving it more susceptible to tree diseases and insects.

So what can the property owner do to help their trees resist being harmed by tree diseases and insects?  Improve and maintain the trees growing environment. According to the International Society of Arboriculture, the single most important thing you can do for your landscape trees is apply a 2-3" layer of good organic mulch around the base every 1-2 years. It is much better to do this than to apply synthetic chemical fertilizers, which only last so long and then need to be reapplied. Applying good organic mulch allows the nutrients to naturally form as they do in a forest, in a natural way, thus allowing the trees to be resistant to tree diseases, without having to toxic chemical fungicides when they become sick. The mulch also helps retain moisture, so as long as the tree is getting adequate irrigation, this it will help it to survive periods of drought.

Doing this should help your trees not only be more resistant to tree disease, but also be more healthy, lush, and beautiful!