Ditylenchus destructor Thorne - Potato Rot Nematode

Ditylenchus destructor, potato rot nematode (PRN), is a tiny roundworm that can cause significant damage to the underground parts (roots, tubers, bulbs) of host crops. Such crops include potatoes, sugar beets, carrots and garlic.

PRN can reduce harvest yields of host crops and cause additional damage during storage. While PRN poses no risk to human health, the nematode can affect international trade of certain commodities (especially potatoes).

Distribution

PRN is a regulated quarantine pest in Canada under the Plant Protection Act, which is enforced by the CFIA. It has been detected in parts of Canada, the United States, Mexico, Africa, Asia, Europe, Oceania and South America.

Slow to move on its own, PRN primarily spreads through infested planting material [e.g. tubers - potato, rootstock, rhizomes and bulbs (especially Iris)]. Infested soil attached to planting material, machinery and vehicles may also carry the nematode. As well, irrigation or flooding can contribute to short distance travel.

Detection and diagnosis

Signs of PRN above the ground are rare. Heavily infested potato plants may be smaller and have curling, smaller and discoloured leaves.

Infestations of iris and tulip bulbs tend to begin at the base, causing grey to black lesions that extend upward, blackened roots, and leaves that develop poorly with yellow tips.

Early infections in potatoes can be seen by peeling the skin to reveal off-white spots that later will enlarge, darken, and become mealy in texture. Badly affected tubers may demonstrate slightly sunken areas with cracked and wrinkled skin, detached in places from the underlying flesh, deteriorating further in colour from greyish to dark brown or black.

Unlike certain other nematode species, this nematode lacks a protective resting stage and is unable to survive through extended periods of desiccation (drying). Thus, PRN is usually only an important plant parasite under cool, moist conditions. PRN over-winters on leftover plant debris or in soil (as adults and larvae), where it can multiply by feeding on a wide range of other plant hosts. It may also over-winter as eggs.

Hosts

Potatoes are the principal host, although the nematode may also attack other crops such as

• iris
• carrot
• dahlia
• garlic
• gladiolus
• onion
• sugar beet
• sweet potato
• tulip

At least 90 crop and weed species (such as dandelion, plantain and mint) serve as hosts. PRN is also known to feed on a broad range of soil fungi.

Best management practices

Once established, potato rot nematode is nearly impossible to eliminate because it can survive on a range of other hosts and soil fungi.

Although a new generation of PRN will be produced each time a host crop is grown, some practices help reduce and manage the nematode population over time.

• Avoid moving potentially infested plant debris and soil onto other agricultural land through shared farm machinery, equipment, or tools.
• Clean and disinfect all equipment before going to a new farm or going between fields.
• Be sure all commercial transport vehicles are free of plant debris and soil.
• Plant certified seed produced on land determined not to be infested with the potato rot nematode.
• Avoid continual planting of a crop in the same field(s) and rotate with non-host crops.
• Contain plant debris, water and soil during crop washing.
• Segregate crops in storage; products of each field should be stored separately.
• Plant cover crops when fields are not in use, so that wind and water do not move soil.
• Keep hedgerows or sod barriers between fields and along highways.

Regulatory controls

If PRN is detected, immediate regulatory measures are taken to contain potential spread. Potato rot nematode is a regulated quarantine pest in Canada and any suspected infestation must be immediately reported to a local CFIA office.