This is especially critical in the fall and early winter when warm days give way to cool nights. Under these conditions relative humidity levels can rise rapidly, often resulting in dew formation on plant surfaces. Heating and properly venting the house can help alleviate this problem. Increasing the air circulation through the plant canopy will also help lower humidity levels and prevent infection. Maintaining a planting density of no more than one plant every four square feet will allow for adequate airflow through the canopy.
Sanitation is also an important disease management strategy.
Washing and disinfecting the inside of the greenhouse and all previously used tray, pots and other equipment will lower the inoculum levels of pathogens in the environment. Do not leave piles of dead plant materials inside or immediately outside the house, as these piles can serve as a source of inoculum for many of these foliar diseases. Varieties of tomato with resistance to leaf mold are available, but at least five races of the leaf mold pathogen exist, so be sure to get a variety that is resistant to all five races, not just one or two. Proper pruning techniques, and proper fertility management will also help in the management of these diseases. Fungicide applications are sometimes required to manage these diseases.