Specialist outlines how to keep greenhouses disease-free

Associate Editor

QUEENSTOWN, Md. (May 30, 2017) — If you’re growing in a greenhouse, it’s important to remember three keys to disease management: Use disease-free soil, exclude pathogens and know how to positively modify your house environment, a University of Maryland Extension specialist said this month.
Greenhouses can boost production and plant development, but they can also stress plants and invite bacterial disease, said Kate Everts to a group of growers and attendees at the university’s High Tunnel Twilight Tour at the Wye Research and Education Center on May 17.
Making sure a greenhouse has ideal water, temperature and light conditions is critical to maintaining healthy plants.
Tactics such as hot water seed treatment can be useful for tomatoes, for instance, she said.
“It’s a good way to exclude diseases from a high tunnel,” Everts said.
Excessively damp soils can inspire disease, and low light intensity can exacerbate issues such as leaf mold, she said.
“It looks a little bit like a downy mildew, but it’s not,” Everts said. “The pathogen is so profuse that it looks fuzzy.”
The tunnels should be positioned with air circulation in mind, facing prevailing winds.
Establishing a 10-meter weed-free zone around the greenhouse is designed to discourage pathogens from entering.
Ideally, that area should slope away from the greenhouse so rainfall doesn’t bring disease in.
It’s critical to pay attention to soil and make sure pathogens aren’t present.
Growers should consider how clean it is where soil is being mixed or soil should be sterilized if mixes aren’t available.
Pathogens such as sclerotia can be particularly insistent, she said.
“They can survive in the soil for many, many years,” Everts said.
Growers can also place foot trays with disinfectant outside greenhouse doorways so pathogens aren’t brought in on boots, similar to what many poultry producers do.
Covering holes and gaps in the greenhouse with insect mesh can also keep problematic bugs from bringing in pathogens.
But making sure you modify your greenhouse to manage moisture is critical, she said.
“This is most easily accomplished by ventilation in greenhouses,” Everts wrote in a report given to growers. “Air flow can be increased by fans that move air around the structure, particularly around vegetable foliage and fruit.
“Improved air movement will also reduce temperature of the foliage as water is transpired. Removing unproductive leaves at the base of plants and trellising are two methods to alter the plant architecture resulting in improved air flow within the foliage.”