Besides spread by vectors, virus can be spread by physical contact of virus with healthy plants. Virus can be released from infected plants and tubers and transferred to healthy plants during many types of physical contact that cause breakage of plant tissues. Release of virus can occur during pruning and handling of plants. Contamination of plant surfaces with virus is not sufficient to cause disease. Infection requires a nonlethal wounding of plant cells for virus to enter healthy plants. Transfer and inoculation can be by tools such as pruning scissors and your hands. The damage required for release of virus from infected plants and tubers and inoculation of healthy plants can by as little as a few leaf hair cells and not be observed. Wind aided physical contact of adjacent plants can also result in release and transfer of virus. Some viruses such as dahlia mosaic virus are sufficiently stable that they can remain active for some time on the surfaces of tools. Virus can be picked up later from contaminated tools and transferred. The key to avoiding transfer of virus is to not handle healthy plants after handling infected plants. Most viruses can be inactivated or removed from hands and tools by washing with hand or dish washing soap. Use soap after coming in contact with infected plants.