Garden Plants | Appropriate Size Sample Needed For Diagnosis
Quite regularly people bring a portion of a plant to myoffice wanting to know what’s wrong with it. Most often the problemcan be diagnosed, but occasionally it’s impossible to diagnosebecause the sample is not an appropriate size. So, what is an”appropriate size?”
For most tree problems”the most difficult to diagnose”one leafor a few needles are not enough. Let me use fire blight as anexample to show the importance of having an adequate sample. Fireblight”a bacterial infection of apples and pears”causes leaves toturn brown to black as if they were scorched with fire. However,leaf scorch, caused by lack of water, also turns leaves brownmaking it impossible to diagnose the problem from a single leaf.Fire blight, though, can be distinguished from leaf scorch by thebending of the terminal growth on a young stem forming a shepherd’scrook. That’s not to say every tree problem requires a largesample, but it’s always better to bring in more than just oneleaf.
For garden plants, some problems can be diagnosed with a singleleaf. For example, early blight is a fungal disease that affectstomatoes and potatoes. The disease causes lesions with concentricrings on the leaves, so the disease can be identified with a singleleaf.
Then again, verticillium wilt, another disease of tomatoes andpotatoes, is difficult to identify with a single leaf.
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