Disease of the Month - Cucumber Green Mottle Mosaic Virus and Pepino Mosaic Virus

Cucumber Green Mottle Mosaic Virus (CGMMV)

Causal Organism: a type of tobamovirus

Crops Affected: Cucurbits (cucumbers, melons, etc.) – greenhouse cucumbers = primary concern

Disease Cycle:

• Highly infective, extremely stable, viral pathogen that can survive for an extended period in the greenhouse environment
• Yields may be reduced by 25% or more
• May be introduced via infected seed (seed-borne)
• Easily spreads between plants through mechanical transmission
  • May also be transmitted by insect pests with chewing mouthparts)

• Younger leaves are affected more than older ones, with viral activity reduced as leaves age
  • Leaves will have green, light-green or yellow-green spots
  • Veins may remain green
  • Young leaves may be deformed in heavy infections
• Fruits may abort and drop off
  • Fruit size is dramatically reduced in those fruit that do not abort

• Seed (thermal or chemotherapy) treatments may partially reduce transmission
• Ensure that seed lots and new plants are virus-free, either through testing and monitoring
• Monitor the crop carefully for the presence of symptomatic plants
  • Early infection is more serious than infection of an older crop
  • Remove early infected plant material to prevent further spread
• Avoid overlapping crops
• Discard and destroy heavily infected plants
• Remove all plant debris and take it off-site, to avoid re-introduction
• Treat crops with insect pests to reduce spread by insect vector
• Clean and disinfect all greenhouse materials, including all structures, containers, tools, and equipment
  • Ensure that obscure and hard to reach surfaces are also treated (e.g. pipe tops, textured surfaces, structural members)
  • Some disinfection may be done on walkways and corridors during crop production, but cleaning and disinfection must be done between crops
• Place disinfecting footbaths at the entrances of all production bays
• Disinfect clothing, tools and gloves at the end of each row

• Highly contagious viral disease
• Transmitted via mechanical contact between plants and contaminated tools, clothing, footwear, hands and other plants
  • Infection may also occur through contaminated leachate water
  • Spread via bumblebee pollinators is possible, but less likely than hand pollination
  • Spread may also occur via cuttings
• May remain viable on dry material for several months
  • Clothing can be infective for up to 2 weeks
  • In cool, moist, organic debris, the virus can remain infective for an extended period

• More readily observed in fall and winter months during low light and temperature levels
• Plants may appear to have a stunted growing point or “head”
• Distorted growth may be observed, which resembles herbicide injury
• Leaves around the growing point may have dark spots, with necrotic lesions developing further down
  • Scorch-like spots may appear on lower leaves
• Bright yellow spots may appear in some areas
• Stems near the growing point may have brown streaks encircling the entire stem
  • Flower clusters may be affected, resulting in abortion
  • The calyx on infected fruit may be brown
  • Fruit may appear marbled (yellow-red mosaic patterns)
• Plants may be symptomless

• Ensure that plants and seed are disease-free
• Sanitation and strict hygiene throughout all stages is key
  • Move from clean to infected areas, not infected to clean
  • Wear clean/disinfected cloths, gloves, boots, etc. when moving into a clean area
  • Have workers and clothing designated for specific areas of the greenhouse
  • Install foot baths at the entrance to different areas
• Power wash and then disinfect the entire greenhouse structure between crops
  • Clean and disinfect all tools and equipment
  • Clean and disinfect or replace irrigation lines
• Dip tools and gloved hands in undiluted skim milk or an appropriate disinfectant between handling individual plants
• Carefully monitor new plants and developing crops, watching for symptoms
  • Mark infected areas and inform workers, visitors, etc. of appropriate steps to take to avoid spread
• Bag and remove plant debris from the space and destroy promptly