Environmental stresses could possibly be the problem as the plants do have some age to them and both seem to be impacted the same way. I am aware that for portions of Texas, the drought has a role in how healthy plants have been. With extended dry periods, the root systems of plants actually shrink in size while the demand for soil moisture from the needles remains or increases. Without sufficient water, needle loss will occur. Southern and western exposures for the plants are typically those sides that suffer. Suggest you also check for insect damage from insects like spider mites. Remedies include watering the plants during long periods of drought, annually feeding the plants to assist in rebuilding root systems and if insects are present and identified as harmful, appropriate treatments should occur.
