Many problems in the landscape are caused by:
Poor Soil Conditions
Top soil removed, plants growing in heavy clay or subsoil, and or poor drainage often resulting in poor root growth, decline in plant health and eventually death.
Root systems that are planted too deep, planting bags left on, and not taking care of wrap around roots, are major causes of plant decline and death.
Poor Watering Practices
Either too much water causing root rots or too little water resulting in leaf burn, poor growth and eventual death.
Topping, over thinning, and "lollipopping", can produce ugly plants, hazardous trees, and plant failure.
Foliage problems caused by poor soil and lack of nutrients.