Which condition is most favorable to the development of seedling diseases?

• A. Overcrowded seedling flats
• B. Excessive soil moisture
• C. Use of soilless growing medium
• D. Low soil temperatures before germination

Answer: (B)

Excessive soil moisture creates the watery environment seedling pathogens need to infect young plants. When the root zone stays wet, fungi such as Pythium and Rhizoctonia can move quickly, attack the seedling’s roots and crowns, and cause damping-off. The water-filled conditions also limit oxygen around the roots, stressing seedlings and making them more susceptible to infection. Crowding can worsen the situation by raising humidity and limiting air movement, but without the persistent wet conditions the pathogens have far fewer opportunities to take hold. Soilless media and good drainage help reduce risk, but high moisture itself remains the key factor that favors seedling diseases. Cooler, very low soil temperatures before germination tend to slow germination and infection, so they’re less conducive to disease than warm, wet conditions.