Cucumber Green Mottle Mosaic Virus Confirmed in Nova Scotia

Wednesday, September 13, 2023

 Cucumber Green Mottle Mosaic Virus (CGMMV) is a highly infective, highly stable tobamovirus which infects members of the Cucurbit family, including pumpkins, squash, melons, gherkins and bitter gourds. The damage inflicted on the host plant and fruit can be extensive, resulting in significant yield losses. Weeds such as nightshade, pigweed and purslane can serve as alternative hosts between curcurbit crops, however the virus itself can remain infectious for many months on crop residue, soils, and growing surfaces/tools.

Symptoms of infection will vary between species and strains of the virus, however mosaic mottling of leaves is a common denominator across these variables. At the early stages of infection, the cucumber plants will continue to grow and bare fruit. As the infection becomes more severe, fruit mottling and distortion can be observed. The plant itself will eventually stop growing, or show severe distortion. Unlike some other viruses in this group, CGMMV's ideal growing conditions mimic those for cucumber production, creating a scenario that supports rapid propagation of virus particles within infected plants. 

CGMMV is most commonly reported to originate from infected seed, but is also easily spread through contact with inoculated tools/workers and existing wounds on the plant. Chewing/sucking/piercing insects, while not listed as a major source of transmission of this virus, may contribute to spread in an already infected production space. 

What can be done?

There are a handful of things that can be done to reduce the chances of infection, and reduce the risk of spreading amongst the crop once the first symptomatic plants have been identified:

1 - Purchase verified, disease-free seed from a reputable supplier. Seed saved from infected cucumber plants are likely also infected, and with its stable shelf life, the virus could survive for many years. Seed can always be submitted for additional disease testing to accredited labs if you are unsure.

2 - Establishing, and maintaining, strict biosecurity protocols on farm. For greenhouse spaces, this means:
  •    Adhering to an agreed upon order of entry - the most 'valuable' plants, such as seedlings, or newly transplanted crops are visited earlier in the day, before visiting the least 'valuable plants, such as those that are nearing the end of their harvest window. Once you have been 'contaminated' by the lesser value spaces, you will not re-enter the spaces containing the more susceptible crops
  • Wearing clean clothes when working with your crop. These clothes cannot come from the field, or spaces where they may have come into contact with disease-causing agents. The use of greenhouse-designated coveralls or lab coats is a good way to limit transmission of pests and disease from the outside. The same goes for footwear - having designated footwear that is worn in the greenhouse is a good way to limit accidental introductions. Alternatively, the use of footbaths containing virkon, or other sanitizing agents, can limit spread as well. 
  • Designate production supplies to each greenhouse - instead of having one pair of pruners that float around between all the spaces, try and have a set for each production space. Harvesting buckets, carts, and other lower-cost items should not be shared wherever possible, to limit potential movement of diseases and pests across the farm. For larger tools (sprayers, lifts, ladders), adopt a regular schedule of cleaning before/after use to prevent accidental spread.
  • House sanitizing agents (ex. virkon, alcohol, bleach) within each greenhouse for tool sterilization. 
  • Regular cleaning and sterilization of greenhouse tools to prevent build-up over time. This should be done more frequently than just between cropping cycles. The timing will depend on the item - pruners should be cleaned and sterilized very regularly, whereas larger tools like carts may see this less frequently. 
3 - Ensure that your compost/waste plant material pile is located FAR away from your production spaces. Pests and diseases can proliferate in these piles, and easily be carried by wind or wings into your new healthy crops. 
  •     If you have had previous issues with viruses in your space, that plant material should be destroyed, as opposed to composted, to reduce the risk of re-occuring infection
4 - Enforce a strict, regular scouting program on farm, including documentation of location, timing, severity and which pests/disease was spotted. 

5-  Stay on top of your insect pests. Allowing piercing/sucking pest populations to grow only increases the risk of disease transmission throughout the production space once a virus has been identified. 

6 - If symptomatic plants have been identified, contact your commodity specialist. Isolating this area of the greenhouse as best as possible is a good course of action in the meantime, and making sure that infected clothing/tools are not used in asymptomatic parts of the greenhouse. Disease confirmation can be done through the use of immuno strips, or most reliably through an accredited lab, before coming up with a plan of action.
For more information on CGMMV, check out Alberta's 2016 factsheet here

If you have any questions, or suspect infection amongst your crop, reach out to your commodity specialist for further discussion.