Can applying milk to tools or plants be effective in reducing virus transmission?
Milk has been shown to be an effective alternative disinfectant for greenhouse tools to prevent the manual transmission of viruses.
Editor's note: This article was updated on April 8, 2014 to include additional information and resources.
Some people may have heard that spraying plants or soaking tools with diluted wet or dry milk may prevent the manual transmission of viruses from plant to plant. One study that tested milk applications directly to plant, "Transmission, Movement, and Inactivation of Cymbidium Mosaic and Odontoglossum Ringspot Viruses," examined Cymbidium mosaic and Odontoglossum ringspot viruses. The researchers mixed different concentrations of skim milk (10-90 percent) with leaf extracts that were inoculated with the Cymbidium mosaic virus. When tested on the host plant, a Dendrobium orchid, the skim milk mixtures were not effective in preventing transmission of the virus. In a separate study, Clemson University researcher Jim Faust and colleague Losenge Turoop applied a prophylactic milk application on tobacco stock plants and found that it did substantially (approximately 50-80 percent) reduce the spread of tobacco mosaic virus to uninfected plants. Michigan State University Extension states that the efficacy of milk could depend on many factors including the virus type, host species, concentration and the timing of the milk exposure.
Other studies have shown that using dry milk can be an effective sterilizing method for greenhouse tools. Soaking tools for one minute after pruning Hibiscus 'Pink Versicolor' and 'Brilliant Red' infected with Hibiscus latent Fort Pierce virus (HLFPV) in 20 percent nonfat dry milk was effective in preventing the spread of the virus, according to "Transmission, In Planta Distribution, and Management of Hibiscus latent Fort Pierce virus, a Novel Tobamovirus Isolated from Florida Hibiscus." Similarly, soaking tools in diluted nonfat dry milk (20 percent) for one minute decreased transmission of tobacco mosaic virus from infected petunias to uninfected petunias, according to “Surprising Results from a Search for Effective Disinfectants for Tobacco mosaic virus-Contaminated Tools." Another study, "The Transmission of Management of Tobacco Mosaic Virus in a Greenhouse Environment," found that dipping tobacco mosaic virus-contaminated razor blades into 10 or 15 percent milk solutions eliminated the spread of the virus to uninfected tobacco plants. For more information on tobacco mosaic virus or about how milk could be used as an alternative disinfectant, visit Mississippi State’s Extension bulletin, "Plant Doctor: Tobacco Mosaic Virus."
MSU Extension reminds growers that there is no cure for plants infected with a virus. Growers should scout their crop for both symptoms of viruses on plants and for insects that can transmit the Tospovirus (e.g., tomato spotted wilt virus and impatiens necrotic spot virus), such as aphids and thrips. If growers are pinching plants, disinfect tools between cuts. If a known virus problem arises, discard plant material and sterilize benches, trash cans, hands and all other surfaces that may have come in contact with the plant material.
To learn about different types of viruses that affect floriculture crops, see "Common types of viruses of floriculture crops and their modes of transmission." To learn about how to manage these viruses once in the greenhouse, see "How to manage plant viruses in the greenhouse."