Tomato Leaf Mold: A Common Disease in Greenhouses
What is Tomato Leaf Mold?
Tomato leaf mold is a fungal disease that affects tomato plants, particularly those grown in greenhouses or high tunnels. It is caused by the pathogen Passalora fulva, which thrives in humid environments.
Symptoms of Tomato Leaf Mold
The initial symptoms of tomato leaf mold are pale green to yellowish spots on the upper surfaces of leaves. As the disease progresses, the spots turn bright yellow and merge together, causing the foliage to die. Infected leaves curl, wither, and often drop from the plant.
In severe cases, the disease can also affect flowers, stems, and fruit. Infected fruit may become dark in color, leathery, and rot at the stem end.
How Tomato Leaf Mold Spreads
The P. fulva fungus can survive on infected plant debris or in the soil. The disease is spread by rain and wind, on tools and clothing, and via insect activity. High relative humidity (over 85%) combined with high temperatures create ideal conditions for the spread of tomato leaf mold.
Preventing Tomato Leaf Mold
There are several steps you can take to prevent tomato leaf mold in your greenhouse:
- Use disease-free seed. Start with certified disease-free seed or treated seed to avoid introducing the pathogen into your greenhouse.
- Remove and destroy crop debris. After harvest, remove and destroy all plant debris to eliminate potential sources of infection.
- Sanitize the greenhouse. Between crop seasons, thoroughly clean and disinfect the greenhouse to kill any remaining spores of the fungus.
- Control humidity. Use fans and avoid overhead watering to minimize leaf wetness, which creates a favorable environment for the fungus.
- Stake and prune plants. Staking and pruning plants helps to improve air circulation and reduce leaf wetness.
Treating Tomato Leaf Mold
If tomato leaf mold is detected in your greenhouse, it is important to take action quickly to prevent further spread of the disease.
- Apply a fungicide. Apply a fungicide according to the manufacturer’s instructions at the first sign of infection.
- Remove infected plants. Remove and destroy any infected plants to prevent the disease from spreading.
- Quarantine infected plants. If possible, isolate infected plants from healthy plants to prevent cross-contamination.
Additional Tips for Managing Tomato Leaf Mold
- Maintain night temperatures higher than outside temperatures. This helps to reduce condensation and leaf wetness.
- Avoid overhead watering. Water plants at the base to minimize leaf wetness.
- Provide good ventilation. Use fans or open vents to circulate air and reduce humidity.
- Monitor plants regularly. Inspect plants regularly for signs of tomato leaf mold and take prompt action to control the disease.
By following these steps, you can help to prevent and manage tomato leaf mold in your greenhouse, ensuring a healthy and productive tomato crop.
