Best management practices for preventing potato cyst nematode contamination
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Golden nematode (Globodera rostochiensis) and pale potato cyst nematode (Globodera pallida) are microscopic invertebrate roundworms that can cause extensive damage to the roots of host crops such as potatoes, tomatoes and eggplants. While these two species of potato cyst nematode (PCN) do not pose a risk to human health, if left unmanaged these quarantine pests can reduce yields of potatoes and other host crops. PCN has been detected in parts of Canada and the United States, as well as parts of Asia, Africa, Central America, South America and the Middle East.
PCN are a serious risk to the international trade of commodities associated with soil, so every precaution must be taken to prevent their introduction and spread.
PCN is primarily spread by moving infested soil that contains cysts. In rare cases, it is spread through cysts that remain attached to infested root systems. Spread from one field to another occurs through infested planting material (for example, tubers) being moved or through infested soil attached to planting material, machinery, and/or vehicles. PCN can also be spread long distances when infested soil associated with seed potatoes, root stocks or bulbs are shipped to or from a farm.
Detection and diagnosis
While an infested host plant does not present obvious or unique symptoms of PCN infestation, PCN does cause secondary symptoms such as reduced root systems with associated nutrient deficiencies and water stress (Figure 1). If a crop is highly infested it may show wilting, yellowing, reduced plant size and extensive plant death leading to yield losses. In some cases, PCN can be detected by observing cysts on a host plant's root system (Figure 2). If PCN is suspected, soil and/or root samples must be taken for expert analysis to confirm the presence of PCN and to determine the density of the pest population.
Testing for potato cyst nematode
In fall 2006, the Canadian Food Inspection Agency (CFIA) implemented a soil-sampling program to test fields used to produce seed potatoes which are traded between Canada and the United States.
Soil samples are collected along the perimeter area of identified fields, covering a surface that represents 10% of the total field area. Samplers use a scoop to collect 3 samples per acre, where each sample contains 2000 cubic centimetres of soil.
Should a positive or suspect sample be detected, an investigation is immediately launched and sampling is intensified to cover the entire field and gather approximately 8 soil samples per acre.
When Canadian samples are taken to confirm the presence of PCN, they are analyzed in CFIA's laboratories using internationally accepted diagnostic methods. If any cysts are found, nematologists can determine the species of nematode by identifying its form and structure. Further confirmation can be obtained through molecular genetic analysis. Finally, it is important to note that preparing, extracting, and testing soil samples is a lengthy process and usually requires a minimum of 10 to 15 days.
The cyst (Figure 3), contains eggs which are stimulated to hatch when they are in proximity to the roots of a host plant. Once hatched, the larvae will undergo three additional larval stages. The first stage occurs within the egg, while the second infective stage occurs within the soil and the third and fourth maturing stages occur within the plant root.
Second stage juveniles are microscopic and worm-like, about 470 micrometres long with a strong stylet for puncturing cell walls. Adult males are similar in appearance, about 1200 micrometres long with a short bluntly rounded tail. Adult females are spherical, approximately 450 micrometres in diameter.
After entering the host root, the females feed and their sac-like bodies expand to break through the surface of the root. When the males are fully developed they migrate back into the soil. The free roaming males fertilize the embedded females and die shortly after.
The fertilized females then begin to swell as the eggs develop within their bodies. Following death, the female bodies harden and darken into cysts containing 200 to 500 eggs each. Cysts detach from the roots and can lie dormant in the soil for more than 20 years. The globular-shaped cysts are initially pearly white coloured, changing to yellow (only for golden nematode) or golden brown as they mature.
Best management practices
Once established, PCN is nearly impossible to eliminate as cysts can lie dormant in the soil without a host crop for decades. A new generation of PCN is produced each time a host crop is grown. However, there are best management practices to help prevent infection and reduce the nematode population over time:
Minimize soil movement
- Avoid sharing farm machinery, equipment, tools and containers
- Do not spread tare dirt or debris onto agricultural land or areas where it could be spread to other agricultural land (tare dirt or debris is the loose soil knocked off either during potato processing operations or during storage filling/emptying operations)
- Never use bags, containers, etc. more than once for potato transport unless they are free of soil
- Be sure all commercial transport vehicles are free of soil
Keep farm equipment and vehicles clean
- Ensure equipment is available to conduct proper cleaning and disinfection of farm machinery and vehicles
- Clean and disinfect all used equipment before using on a farm
- Clean and disinfect all machinery, vehicles and other equipment before going between fields (includes those of temporary help, custom applicators and utility companies) (Figure 4)
Follow best practices for potatoes
- Plant certified seed potatoes produced on land determined not to be infested with PCN
- Avoid continuous planting of potatoes in the same field(s)
- A long rotation cycle is critical for managing and preventing PCN
- During interim years, plant non-host crops
- Contain water and soil during tuber washing to avoid contaminating farm land
- Processing facilities should not return soil, water, cull tubers and debris to agricultural land (this includes managing and limiting waste used as livestock feed)
- Segregate potatoes in storage – each field should be stored separately
Follow best practices for land
- Plant cover crops when fields are not in use to prevent wind and water from moving soil
- Keep hedgerows, sod barriers or sod strips between fields and along highways to provide a physical barrier to soil movement
- Do not use common headlands, farm roads and public roads as turning areas
- Inform people in your operation of the seriousness of PCN and ensure they follow all necessary precautions
Successful management or eradication of PCN is complex and takes many years. If PCN is detected at additional locations in Canada, CFIA will work with affected parties and industries to develop appropriate long-term strategies to deal with the pest.
These strategies will help protect the local, provincial and national potato industries as well as other affected industries while being sensitive to the situation of positive growers. With appropriate management it will be possible to grow most non-host crops on affected fields and it may, over several years, become possible to grow potatoes in an appropriate rotation
In the event of PCN detection, immediate regulatory measures are taken to contain potential sources of spread. Surveys and investigations to trace the infestation back to an infested field and to trace the infestation forward are also conducted to prevent any further spread.
If you think potato cyst nematode is on your farm
- Report the situation immediately to your local CFIA Office. You have a legal duty to do this under the Plant Protection Act. Reporting the situation also helps prevent further spread of these pests which could contaminate soil on the farms of your friends and neighbours and affect the provincial, national and international agricultural sectors
- Immediately cease all work that could move soil from the suspect field to the rest of your farm
- Do not clean your equipment or machinery as investigative samples may need to be taken from them
PCN causes secondary symptoms such as reduced root systems with associated nutrient deficiencies and water stress.
Photo courtesy: Christopher Hogger, Swiss Federal Research Station for Agroecology and Agriculture.
In some cases, PCN can be detected by observing cysts on roots and tubers.
Photo courtesy: CFIA
Golden nematodes (Globodera rostochiensis) are microscopic invertebrate roundworms that do not pose a risk to human health.
Photo courtesy: Nematology Lab, Ontario Plant Laboratories, CFIA
Clean and disinfect all machinery, vehicles, and other equipment before going between fields.
Photo courtesy: CFIA.
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