Answer: It sounds like your plants have a "plumbing problem". This is usually due to root damage (feeding insects, nematodes, etc.) or a vascular wilt (a fungus that plug us the water supply pipeline in the plant). Dig up a plant in the latter stages of decline. Look at the roots for obvious severed roots or knots from nematodes. Then split the stem lengthwise and look for a brown streak in the area between the outer "bark" and inner stem tissues. This is indicative of a vascular wilt such as fusarium or verticillium. There is no cure for these. You must locate future plantings in a spot that doesn't have the disease or in fresh planting mix in containers.
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