Hello Dennis –
Generally, if the leaves are turning brown at the bottom of your plant it will be an indication of fungal infection. However, there are steps you can take to prevent infections, such as fungal rot, in tomato plants.
• Removed any discolored and diseased branches. Be sure to sterilize your garden tools! We recommend Isopropyl Alcohol.
• If possible, water from the bottom of the plant using a soaker hose. If soaking isn’t an option, be sure to water early in the day to allow plants plenty of dry time.
• Ensure proper spacing between plants to ensure that there is plenty of air flow. Air flow is crucial in keeping fungus, bacteria and mold from forming on plants.
• Apply products designed to treat fungal infection. We recommend Liquinox or Serenade.
• Avoid planting night shade varieties in the infected soil for at least 2 seasons. Plant other garden items, such as garlic, in the affected areas.
Taking these steps will ensure that your tomatoes yield their optimal potential and produce delicious fruits for the long haul!
Cheers!