Q. I have several Carolina Cherry Trees in my yard. Last year the leaves started to turn brown and flake off. I have attached some photos. Can you tell me why they are doing this and how I can correct the problem.
A. I had to study your picture carefully and so some investigating on what might be going on. Let's get one point out of the way before we begin.
This plant is native to the southeastern United StatesIt is not native to the arid and desert southwestern United States. When it is grown in our climate and soils it will struggle compared to growing in the soils and climate of the Southeast. This means it requires extra care on your part when planting and growing it compared to growing it in the southeast.
Add amendments at the time of planting
Carolina Cherry Laurel here it is very important to add 50% compost to the planting mix and dig the hole at least three times the width of the container. Five times is better. Never cover the soil above the plant roots with rock. Always use organic mulches or groundcovers on top of the soil a distance equal to at least the diameter of the plant canopy. This would chip mulch, not bark mulch, should be at least 4 inches deep and renewed every 2 to 3 years as it "dissolves" into the soil as it decomposes and adds nutrients and organics back to the soil. This is very important for this plant. I believe that this is the reason why you are having problems with this plant in your location.
Many of the same problems as plums and peaches
The major problems with this plant, because it is so closely related to plums and peaches, are many of the same problems as fruit trees. When I look closely at the pictures you sent, which are very good and thank you very much, I see root weevil damage on the leaf edges. These are the notches that you see on the margins. These insects feed at night and are in the soil beneath the plant. There is not much you can do about them except perhaps apply a systemic insecticide around the roots after the plant has finished blooming. Use the Bayer insecticide if you go down this route.
The second problem is probably the reason you are most concerned. This is the discoloration and death along the margins of the leaves. I believe this is primarily a water/fertilizer/pruning problem. Let me explain why.
I believe if these plants were in good health you would see little to none of this type of damage. I believe the plants would be very full and the leaves would appear healthy. Make sure you apply either wood chip mulch around the trees as I suggested earlier and combine that with a yearly application of a tree/shrub fertilizer in late January or early February. Only use mineral fertilizers if you have wood chip mulch surrounding the trees. Again, I repeat. This should not be bark mulch if you want to improve plant health. Don't get me wrong. There is nothing wrong with bark mulch. It can be very beautiful but it adds nothing to the health of the plants. It is purely decorative. Wood chip mulch, trees and shrubs that are shredded in their entirety and applied to the soil surface, improve plant health when they begin to break down/decompose a.k.a. "melt" or "dissolve" back into the soil.
Irrigation should never be daily.Give these plants at least one day without irrigation so that water can drain from the soil. The roots of these plants are very susceptible to suffocation a.k.a. root rot when soils remain wet and cannot drain adequately.
Another problem with this plant is a plant disease called shot hole fungus. We see this leaf disease on peaches and plums when our humidity is too high. In climates with higher humidity, like some of those in California, this disease can be a severe problem. In fact, varieties of peaches and plums are grown in certain areas with high humidity strictly because of this disease problem. This disease causes spotting on the leaves and sometimes the leaf margins. As this disease worsens, sections inside of the spots die and drop from the leaf leaving "shot holes". Some varieties of plants are much higher susceptible than others. If the health of the plant is improved, I am guessing this disease will disappear or minimized.
Improve the soil and drainage. You can do this by drilling holes in the soil with an auger as deep as possible. Fill these holes as best you can with compost. This will improve the soil and improve drainage. Cover the soil with wood chip mulch at least 3 to 4 inches deep. Fertilize with compost this year and next year you can use a mineral fertilizer if you wish provided wood chip mulch has been on the surface of the soil for 12 months. Avoid daily irrigations.