The smallest and most difficult to control of all microorganism pathogens. Plastic mulch reflects ultraviolet light which repels insects like that carry various devastating diseases including viral diseases. University research using silver colored plastic mulch has been used under tomatoes and other plants to show significant insect control. Although it may work we don’t really like it as much as natural mulch. Mosaic viruses destroy chlorophyll causing leaf yellowing. Another virus blocks the plant’s vascular system, restricting the flow of water and nutrients. Viruses are transmitted by vegetative propagation, in seeds, on pollen, and on tools and gardeners’ hands. Viruses are also transmitted by insects, mites, nematodes, and parasitic plants. Viruses slow plant growth and reduce yields. Infected leaves may deform and develop mottling, streaking, or ring-shaped spots. Identification is sometimes the elimination of all other possible causes. Purchase certified plants, control insects that spread viruses and remove and thoroughly compost all infected plants. We have several reports of curing mosaic virus with a spray of 2% generic hydrogen peroxide or one of the commercial products like BioSafe.