A Tree evaluation may be needed as these symptoms may be the cause of many factors (disease, insects, fungal infections) but most commonly it ends up being a Non Living irritant to the tree. So I will go over why your leaves may be yellow, browning or dying in San Antonio.
Chlorosis is the first condition that decreases the amount of chlorophyll in the leaves giving them a yellowish color. The source cause of the chlorosis could be from poor planting, damaged roots, poor temperatures, pollution, lack of nutrients and inconsistent soil moisture.
All of these factors we can control to some degree on our own although the treatments may be short or long. It is highly important to get the chlorosis under control as chlorophyll is the most important part of photosynthesis and will damage the tree in the long run.
Do an inspection, that is a good start, has there been any soil disturbances? any change in moisture? any change in soil temperature? (for temp. consider mulching or heat bulbs) If the answer hits you in the face take care of it and monitor the leaves over the coming months. If the chlorosis is a result of poor nutrition you may need a soil sample taken to evaluate the contents of your soil. Often the PH balance in your soil can be tampered with by landscapers trying to get the grass green, a pre emptive effort may be to use a complete fertilizer 2X a year to balance the soil. (I recommend late summer and spring. It is important to have the soil fertile in fall as a tree absorbs the energy and prepares then for the next years spring growth, a good fertilizing before fall can increase your yield come spring)
Leaf Scorch is the second reason why your leaves may be yellow, browning or dying in San Antonio. This is generally identified by browning or dying of the area between the veins of a leaf. It is caused by lack of moisture in the leaf. The early symptoms of leaf scorch can appear to be chlorosis, yellowing and drooping so in early stages it may be hard to identify.
The question you have to ask yourself is why is your leaf not getting moisture? The answer may be found as a needle in a haystack. Is it pests-borers that have bored through the stem? is it environmental such as drought? is it some form of soil contamination like PH balance change? Is it a tree that was planted in a small hole surrounded any compact soils and the roots have nowhere to go? Has a root been cut lately by a plummer or mason doing construction work? Was there an unusual freeze or frost? These are some of the questions you must ask.
First order is to rule out pests. Maybe knock off some upper leaves, stems from the crown and inspect them with a glass to see the little buggers. If you see nothing inspect the branches and truck for holes. If nothing is found at this point it may be time for a soil sample. If you choose to skip this I would do the same as above recommendation and use a complete fertilizer and get your tree on a regular watering cycle. How much water is different in each case because of different soil compositions, if your soil is compact be careful not to over water because the lack of drainage could cause root rot and other fungi. If you have well drained soil it may be in need of a fertilizer and more frequent watering. Remember, “Do Not” water in winter. A tree is unable to absorb during this time and you may do damage.
I hope all of this has helped in finding out why your leaves may be yellow, browning or dying in San Antonio. I wish you the best and hope your tree’s do well. As always we are here to help if need be.