What do you see on other plants?

What do you see on other plants?

Now take note of the condition of surrounding plants. Are other specimens similarly affected? What is their general health? If you are looking at a grouping of a particular species, does symptom severity seem to relate to any kind of gradient of drainage or sun exposure? Trying to answer such questions often provides key clues about major environmental factors. If, for example, a number of different vegetables in a garden are all dying, it is unlikely they are deteriorating from an infectious disease since most disease-causing pathogens have limited host ranges. It is more likely that some environmental factor, such as extended flooding or poor soil conditions, is involved.
Often noticing what is occurring on overhanging plants can prevent embarrassing misdiagnoses. Scale insects, which suck sap from plants, excrete this processed sap out the other end in the form of “honeydew.” Often this clear, sugary, sticky liquid becomes covered with a sooty mold fungus that simply grows on the sugary substance, rather than plant tissue itself. Calico scale is a prolific producer of honeydew. Consider what happens to the leaves of plants underlying a tree that is heavily infested with this scale insect. The underlying plants are not infested; however, their leaves become blackened with sooty mold. Of course, an effective treatment must focus on the scale infestation rather than non-infested plants with blackened leaves.