Greenhouses isolate plants from the bug- and disease-infested world outside. However, the same qualities of greenhouse growing that protect plants from the problems experienced by their outdoor-growing brethren also means that, once a disease arrives in the greenhouse, it can quickly spread out of control. Careful practices prevent diseases from taking hold in the greenhouse.
The greenhouse owner who can identify how diseases enter the greenhouse is best prepared to control them, according to the Pennsylvania State University Cooperative Extension website. Greenhouse diseases enter through outside sources, including contaminated soil, water and air. Living and dead plant material, especially plants brought from other greenhouses, may harbor pathogens.
Greenhouse plants are susceptible to the same diseases as plants grown outdoors. The difference is the comparative speed with which greenhouse diseases spread. Fungal, bacterial and viral diseases spread rapidly through greenhouse plants, according to the North Carolina State University Plant Pathology Extension website. Insect pests found in greenhouses, such as thrips and aphids, also carry disease.
Your greenhouse should maintain conditions ideal for growing plants but not conducive to disease. The North Carolina State University Plant Pathology Extension recommends checking that soil drains properly and that adequate air flow keeps plants dry and well-ventilated. Make sure that leaky hoses or dripping supports don't cause standing water or keep plants wet constantly. Watering practices should assure foliage has time to dry. The greenhouses should have no weeds or free-growing plants.
You can transmit diseases from one plant to another in a greenhouse by using contaminated equipment, tracking in dirt from the outside or even handling plants with dirty hands. In his recommendations for limiting diseases in greenhouse operations, Pennsylvania State University Cooperative Extension plant pathologist Gary W. Moorman reminds on the school's website that no detail is too small. Even hand trowels left on the ground can pick up pathogens tracked in from outside and then spread into the plants' soil.
Five percent bleach solutions and soap handle most needs for sanitation in the greenhouse, according to the North Carolina State University Plant Pathology Extension. Foot baths prevent you from tracking in dirt and pathogens from the outside. Wash and sanitize all tools and your hands between uses and sanitize seeds before planting.