Answer: Based on your description it is difficult to make a definite diagnosis, but I would suspect there is a problem with the soil or some other aspect of the environment. Soil problems could include excess fertilizer in the planting hole, a clogged drainage hole in the bottom of the container, or perhaps water holding polymer being poorly distributed in the mix. If that particular spot has poor air circulation or lack of light or excess reflected heat compared to the others that might explain it too. Finally, it could be a soil borne disease, imported with the first plant and being passed on to the others. To remedy this you would need to replace the soil and also wash out the box with a solution of household bleach and water, one part bleach to nine parts water.
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