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How To Treat Your Brown Tomato Plant Leaves
Brown leaves on tomato plants typically come from disease, pests, or dehydration. If you can whittle down the list to a few possibilities, you should be able to address the issue.
If your plant is dehydrated, remove the dead parts and change your watering schedule moving forward. Tomato plants need 1 to 2 inches of water per week depending on the rain.
Another possibility is spider mites, which are tiny little pests that suck the sap out of plants. You can get rid of them by washing them off with water or using insecticidal soap.
Otherwise, disease will likely be the culprit. In that case, the best thing that you can do is remove the affected leaves to prevent the problem from spreading.