Numerous important pathogens of vegetables can overwinter more effectively in greenhouses and high tunnels, as compared to field environments. These include pathogens that cause foliar diseases like leaf mold, gray mold, and powdery mildews. In addition, soilborne pathogens, like root knot nematode and vascular wilt fungi, can also persist easily in greenhouse soils.
Foliar Disease Cleanup Tips
To reduce pressure from foliar fungal diseases in greenhouses, remove all debris from this cropping season soon after harvests are complete. This includes leaves, stems, root systems, and fallen produce. Some growers have adopted the use of landscape fabric as mulch in cropping areas and walkways because debris can quickly be swept out of the greenhouse during the season. Crop debris should be disposed of at least 500 feet from any future cropping site, or alternatively, could be burned or thrown in the trash.
If the crop has had a foliar bacterial disease, such as bacterial spot (Figure 1), speck, or canker on tomato, destroy or sanitize trellis materials well to reduce pathogen carry-over. Wooden stakes do not efficiently sanitize, so those should be replaced from any section of the crop that was affected (also applies to viral diseases). Metal trellis materials can be sanitized in 10% household bleach (1 part bleach to 9 parts water). Greenhouse posts and beams should also be sanitized with 10% bleach or greenhouse sanitation products. Whenever metal materials are cleaned with bleach, follow soon after with a fresh water rinse to prevent corrosion.
Stem and Soilborne Disease Cleanup Tips
To reduce pressure from soil-associated diseases, plant roots should also be pulled up and exposed to dry air conditions, then carried out and burned or trashed. Avoid dropping materials as the debris are removed from the greenhouse. This is particularly helpful for growers with histories of root knot nematode, Fusarium wilt, or Verticillium wilt. Resistance to each of these specific diseases is available in commercial production varieties, and is recommended every season after one of these diseases is diagnosed. If a soilborne issue has arisen this past season, consider replacing the mulch to avoid carrying over or spreading the causal pathogens.
For plantings that have had pressure from southern blight or timber rot, carefully pull plants and attempt to remove as many fungal sclerotia as possible from the cropping area. Sclerotia are overwintering bodies of the causal fungus that will serve as sources of disease during the next cropping cycle (Figure 2). Deeply tilling any remnants of plant debris after crop removal will further bury disease-causing organisms.
If greenhouse space and vegetable market considerations permit, start planning your greenhouse rotations now. While rotation generally provides minor benefits for veggie foliar disease management, it can be extremely valuable to reducing or containing soilborne diseases in greenhouses. Rotate out of a susceptible crop in an affected area for at least 2 seasons; longer rotations are even more effective at reducing disease pressure.
- IPM Scouting Guide for Common Problems of High Tunnel and Greenhouse Vegetable Crops in Kentucky (ID-235)
- Managing Greenhouse & High Tunnel Environments to Reduce Plant Diseases (PPFS-GH-01)
- Root-knot Nematode In Commercial & Residential Crops (PPFS-GEN-10)
- Greenhouse Sanitation (PPFS-GH-04)
- Bacterial Canker of Tomato (PPFS-VG-06)
- Bacterial Spot of Pepper & Tomato (PPFS-VG-17)
- Southern Blight (PPFS-GEN-16)
- Vegetable Cultivars for Kentucky Gardens (ID-133)
By Emily Pfeufer, Extension Plant Pathologist and Kim Leonberger, Extension Associate