Tobacco Mosaic Virus on petunia. Photo: T. Ford, Penn State
Historically when a call would come into the office about yellowing petunias I would load up my pH meter and my box of calibration solutions and would head out to the greenhouse operation to confirm the grower's suspicion that they were having a media pH issue. Unfortunately, over the last several years the yellowing observed by growers in their petunias was not media related and instead could be linked to a virus issue in the greenhouse.
Plant viruses like Tobacco Mosaic Virus (TMV) make even the heartiest of growers shudder since confirmation of its presence in the greenhouse can translate into the disposal of thousands of dollars of plants. Tobacco Mosaic Virus can readily be transmitted to plants through the use of contaminated pruning knives, scissors, workers' hands, and even on workers' clothing. This is called 'mechanical' transmission. While the initial source of a TMV infection could be attributed to contaminated seed or infected plugs and cuttings, I seem to be visiting the same operations over and over again to deliver the same diagnosis. So, either these greenhouse operations have very bad luck or is there an underlying cause that makes these operations more susceptible to TMV infections.
In each of these operations the workforce is very transient and the owners makes no investment in training or coaching their employees. The employees smoke outside the greenhouse and never wash or sanitize their hands between handling their tobacco products and handling the plant materials. In addition, the scissors used to cut plants back are blackened with plant sap and have never been dipped in alcohol or even a bath of milk to deactivate the TMV virus.
Labor management experts state that "profitability starts with people". This is true even when working with a transient workforce. If your workers are not trained and motivated to practice good sanitation in the greenhouse they can become the weak link in your defense against plant virus diseases like TMV. A few hours of employee training is a small investment to make when considering the ramifications of a TMV outbreak in your operation.
This article also appears on the eGrow Blog. Penn State Extension educators are regular contributors and Penn State Extension is a collaborating organization in e-Grow. e-GRO (Electronic Grower Resources Online) is a collaborative effort of floriculture specialists to create a new clearing house for alerts about disease, insect, environmental, physiological and nutritional disorders being observed in commercial greenhouses. Information is available about disorders, podcasts, and research. Bringing together some of the leading specialists from universities around the USA, e-GRO is a free resource and learning tool for anybody involved in greenhouse plant production.