Damping Off

• Heirloom tomato seeds sometime fail to germinate or die shortly after they do. To help prevent this, start seeds in a soil-free potting mix, because soil can contain pathogens such as fungi that cause seedlings to rot at the soil line. Also, avoid covering seeded flats with plastic to encourage sufficient airflow.
  
  

Yellow Leaves

• Hybrid tomato varieties of today are often bred for resistance to diseases. Heirlooms can be subject to various wilts, fungal infections and viruses that can cause leaves to turn yellow and die. Fusarium wilt is one of the diseases that can attack heirloom tomatoes, causing plant death before maturity.
  
  

Tomato Hornworms

• These large larvae of a moth can be very destructive to heirloom tomato plants and forming fruit. Heirlooms have no defense against tomato hornworms, so you must hand pick to control them or dust your plants with the natural soil bacterium Bacillus thuringiensis.