Consider pesticide applications, recent construction or digging, and weather conditions. TIME Determine when the symptoms became apparent. The onset of a problem may be due to a cultural practice, the seasonal appearance of a disease or insect, or a weather-related event. Remember that long-term stress is slow to appear, taking a year or more at times. This may indicate it is a pathogen.
Diseases are usually species-specific.
Problems caused by environmental factors do not spread, although the symptoms may become more severe. You must know what the plant should look like to be able to determine abnormalities. Check the references to see what problems are typical for a particular species. Gather all the information you can to help you make the diagnosis. Remember that there is usually no single cause.