The Q&A Archives: Brown On Plants

Question: Hi! I was wondering why on my zinnias, there is like a brownish-like dry spot on the stem on a couple of plants. then they get weak, and bend at that site. the rest of the plant seems healthy. The same goes for my marigolds. the leaves on them get brown, then the whole plant dies! I give them proper care, pruning of the dead-heads, water, including Miracle-gro once a week. Can someone tell me what's going on?

Answer: Based on your description I would suspect any one of a number of bacterial or fungal problems, all of which would be encouraged by wet foliage due to either excess rain or frequent overhead watering and worsened by overcrowding or lack of air circulation. They can be spread by working on the plants when they are wet and may winter over on old plant debris, too. The zinnia problem sounds like it could be stem cankers caused by alternaria leaf spot in particular. The marigolds might be suffering from a stem or root rot, possiby caused by botrytis. You might want to check with your county extension (461-1000) for a more specific diagnosis and suggested remedies, if any. I'm sorry about your plants.

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