Varied concentrations can be used on tools or plants.
Some people may have heard that spraying plants or soaking tools with a diluted wet or dry milk may prevent the manual transmission of viruses from plant to plant. The only published study to our knowledge, “Transmission, Movement, and Inactivation of Cymbidium Mosaic and Odontoglossum Ringspot Virsuses,” that tested milk applications directly to plants was one examining 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. 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.
While there are very few studies testing the efficacy of milk sprayed onto plants, 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 Hybiscus 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 a diluted nonfat dry milk (20 percent) for one minute decreased transmission of tobacco mosaic virus (TMV) from infected petunias to uninfected petunias, according to “Surprising Results from a Search for Effective Disinfectants for Tobacco mosaic virus-Contaminated Tools.” For more information on TMV 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 viruses 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.