Organic growers are increasingly choosing to grow year-round in high tunnels, in part to avoid the diseases encountered by field crops. Not only do high tunnels provide physical exclusion from airborne disease, but the environmental conditions necessary for the presence of many disease pathogens simply do not occur in high tunnel production.
Of course disease is not eliminated entirely in high tunnels. Among many others, leaf mold (Fulvia fulva), bacterial canker, Verticillium wilt, gray mold (Botrytis cinerea), white mold (Sclerotinia sclerotiorum), powdery mildew, Alternaria leaf spot, and root rot complexes are all common afflictions of vegetable crops under cover. Once present, the spread of disease is usually swift and the damage can be severe.
The key to successful disease control in high tunnels is prevention. Below are some tips to keep in mind when planning for and managing disease pressures in high tunnels for any season.
- Low air circulation and high relative humidity pose the two greatest threats to a healthy high tunnel environment. Be sure to maintain adequate ventilation and regular air movement, especially in humid weather.
- Select disease-resistant varieties that are well-suited to your growing climate. We’re fortunate to have a long list of resistant varieties that don’t sacrifice flavor and yield.
- Just like us, healthy plants stay healthy. By providing adequate fertility and water for optimum plant growth, you provide your plants with the tools to fight off disease pressures and avoid the most detrimental effects of infection.
- Practice crop rotation whenever possible. Soil-borne diseases can be one of the hardest problems to avoid in high tunnel production. When rotation is not an option, many tomato growers have turned to grafting their tomato plants onto vigorous rootstock varieties less afflicted by root rot.
- Providing adequate plant spacing is essential in encouraging air flow and avoiding excessive shading. This may mean reducing plant populations below field standards.
- Diligent pest management practices can significantly reduce disease pressures. Try to keep high tunnels free of weeds which harbor disease and the insects which transmit them.
- Practice good sanitation by removing diseased crop residues and sanitizing tools, equipment, trellis, and mulches. If a high tunnel is empty in the winter, leave the structure exposed to the elements so that disease spores can be killed by winter weather.
There are many excellent resources available for growers using high tunnels. Take a look at the below links for more information.
- University of Vermont High Tunnel Guide by Ted Blomgren and Tracy Frisch http://www.uvm.edu/~susagctr/Documents/HighTunnels.pdf
- Disease Management in High Tunnels by Janna L. Beckerman, University of Minnesota http://www.extension.umn.edu/distribution/horticulture/components/M1218-9.pdf
- Cornell University Department of Horticulture High Tunnels Site http://www.hort.cornell.edu/hightunnel/