Viral Disease of Plants

Plants can suffer from viral attacks just like humans.  However, there is a major difference. Plant viruses must enter the plant through a wound. This may be the result of natural growth, mechanical injury, insects that puncture, or other plant infections. The two most common of these are insects and mechanical injury, although viruses can be transmitted by pollen or by seeds. Common insects that cause viral diseases are thrips and insects that have piercing, sucking mouthparts like aphids, planthoppers, leafhoppers, whitefly, scale and mealybugs. Mechanical injury can occur when pruning, repotting, or propagating by budding or grafting.

Just as in the case of a human virus, there is no known cure. Also, some plants may be infected but show no symptoms – either the virus has not reached optimum conditions, or not every component of the virus is in place for symptoms to appear.

Common viral diseases include rose mosaic virus, peony ring spot, common bean mosaic virus, impatiens necrotic spot virus and tomato spotted wilt virus. It is costly to diagnose a virus; usually, a special test needs to be done. Common names are often based on symptoms. Common symptoms include mottling (called mosaics) that looks like a variegated yellow and green on the leaf, fruit, or flower; curled or distorted leaves that are thick and rigid on a wilting plant; stunting of leaves, stems, or fruit; ring spots that look like wavy rings or lines of yellow, white or red throughout the leaf tissue; or blackened cankers or black streaks on the stem.

Control

• Because there is no known cure, infected plants need to be removed and destroyed.

• Prevention is extremely important.
  • Healthy plants are less susceptible. Be sure to supply regular micronutrients (like those in kelp meal or liquid seaweed) and beneficial microorganisms such as EM-1 or compost tea.
  • Control the insects that may be bringing in viruses. See controls for Aphids and other soft-bodied insects or Thrips. This includes insecticides like Neem oil products, Monterey Insect Spray, SucraShield, Mycotrol O or Pyganic. Start using insecticides when you get 10 insects on a sticky trap per week. Visually inspect also to monitor their populations.
  • Clean all pruning or propagating tools with Botani-Wipes.
  • If at all possible, isolate incoming plants for at least 7 days. Check for the insect vectors or signs of viral disease.
  • Destroy all weeds; they can harbor insects or a virus.
  • Rotate your crops in your garden.