Potatoes

Maximum potato returns can be obtained by managing nematode populations before they start doing damage – and threatening profitability.

Nematode infestation of a potato crop often results in the decline of potato returns and/or the reduction in the quality of potatoes. Nematodes can cause direct damage that may result in complete crop loss, or a reduction of the sellable crop. 

The most common nematode species in the Pacific Northwest are root-knot, stubby-root and root-lesion. There are several other nematode species that are associated with reducing yield and profitability.

Columbia root-knot nematodes

  • Location: Columbia root-knot nematodes, which are sedentary endoparasitic nematodes, are found in abundance, especially in sandy and organic soils. They can be found in localized areas or, in some cases, the entire field.
  • Symptoms: Above-ground symptoms of Columbia root-knot nematodes are typically absent, but can include a rough and bumpy texture, or galling, on the tuber surface. Brown spots occur on the vascular tissue. Other symptoms include late-season stunting, chlorosis, wilting and nutrient deficiencies.
  • Damage: Damage from Columbia root-knot nematodes is commonly around 25 percent, but can range from slight to 100 percent. Columbia root-knot nematodes can cause significant damage in both warm and cold climates. Total loss is possible due to tuber marketability. Due to rapid development and number of generations of Columbia root-knot nematodes, the threshold level is one in many growing regions.

Stubby-root nematodes

  • Location:Stubby-root nematodes, which are migratory ectoparasitic nematodes, are found in isolated sandy, moist soil areas, usually between 8 and 16 inches deep. The mobility of the stubby-root nematode allows it to occasionally travel at depths of deeper than 2 feet.
  • Symptoms: Symptoms of stubby-root nematodes include irregular-shaped patches in the field, stunting, poor stand, nutrient deficiencies and stubby roots. Feeding by stubby-root nematodes often cause root tips to stop growing, resulting in lateral roots that become stunted themselves. This leads to a series of stunted roots that are incapable of taking up an adequate supply of water and nutrients.
  • Damage: Damage from Columbia root-knot nematodes is commonly around 25 percent, but can range from slight to 100 percent. Columbia root-knot nematodes can cause significant damage in both warm and cold climates. Total loss is possible due to tuber marketability. Due to rapid development and number of generations of Columbia root-knot nematodes, the threshold level is one in many growing regions.

Root-lesion nematodes

  • Location:Root-lesion nematodes, which are migratory endoparasitic nematodes, are typically found in abundance, especially in sandy and organic soils.
  • Symptoms: Symptoms of root-lesion nematodes include internal browning, chlorotic foliage, deteriorated roots, premature senescence and early death. High levels of infection can result in reduced root and shoot growth. Lesions are long, yellowish to brownish markings that can resemble cat scratches.
  • Damage: Root-lesion nematodes are endoparasites that feed and reproduce inside and outside plant roots. All phases can penetrate roots and move from cell to cell, resulting in cell death and brown lesions on the roots. Yield losses can be considerable when high populations are present as root-lesion nematodes (specifically the Pratylenchus penetrans species) weaken potato plants, making them more susceptible to diseases like verticillium wilt. Overall, root-lesion nematodes cause weak, shallow root systems with a significant amount of dead areas.

Nematodes are microscopic worms that feed on the plant tissue and root system of potatoes. They can remain stationary or move through the soil, and can live either inside or outside of roots, impairing the root function. By reducing the root's ability to uptake water and nutrients from the soil, nematodes cause poor growth, low yield, deficiency symptoms, a poor root system and cosmetic damage to the sellable crop.

There are two basic types of root-parasitic nematodes: endoparasitic and ectoparasitic. Endoparasitic nematodes enter and feed within the root system, and include root-knot, lesion and cyst nematodes. Ectoparasitic nematodes feed exclusively from outside of the root tissue and include stunt, stubby-root and sting nematodes.

Symptoms
Typical symptoms of nematode injury can involve both above-ground and below-ground plant parts. The following are symptoms of a nematode infestation:

  • Galls on the roots and cosmetic defects on the surface of the potato
  • Stunting and reduced vigor
  • Sunken, dark-colored pits or skin cracks
  • Poor root development and plant uniformity
  • Premature wilting
  • Slow recovery to improved soil moisture conditions
  • Leaf chlorosis (yellowing)
  • Brown spots within vascular ring

Plants exhibiting stunted or declining symptoms usually are found in patches of nonuniform growth as opposed to an entire field exhibiting an overall decline of plants.

Injury symptoms in potatoes are related to the type of nematode, nematode population density, crop susceptibility and current environmental conditions. For example, under heavy nematode infestation, growth of young plants may be restricted and, therefore, could develop a stunted condition.

Under less severe infestation levels, symptom expression may be delayed until later in the season – after a number of nematode reproductive cycles have been completed. In this case, above-ground symptoms will not always be apparent early in crop development. Symptoms will become more pronounced over time, and reduction in root system size and function may be experienced.

Plant symptoms and yield reductions may be directly related to preplant infestation levels and other environmental stresses imposed upon the plant during crop growth. As infestation levels increase, so then does the amount of damage.

Management of nematodes starts with the development of a nematode management plan. A soil sample of the field should be taken first to see if nematodes are present, followed by consulting field histories and crop rotations. When populations are not present, practices should be implemented to prevent introduction. Soil samples that test negative for nematodes do not guarantee that a field is free of nematodes.

After reviewing soil samples, assess nematode management options to design and implement a successful nematode management plan that will meet the needs and goals of your operation. It's important to remember nematode populations are extremely variable. When making a nematode management decision, it's important to review field histories, crop rotations and a current soil sample.

Four items are important for effective nematode management:

  • Use of healthy seed material
  • Crop rotation
  • Chemical control
  • Preventing reinfestation

Use of healthy seed material
Plant only certified potato seed that has originated from a limited generation program. Do not plant year-out or eliminator seed. Growers should obtain a copy of seed certifications with the consent of the seed grower. A document called a plant health certificate is used by certification agencies in the United States and Canada, and can be requested from the responsible agencyin the state where the plants, or slips, were grown. It lists information such as summer and winter test results, certification pedigree of seed, certification lot numbers, seed class and farm history. A soil sample also should be taken from seed tare dirt to determine the presence of nematodes.

Crop rotation
Crop rotation and cropping sequence impacts nematode populations and are important considerations for the management of potato nematodes. Crop rotation with unrelated crops is a sound practice for reduction of several soil-borne problems. Growers should consult with a university representative to determine the appropriate rotation pattern for managing nematodes.

Chemical control
Telone® II soil fumigant, or Telone C-17 fungicide and nematicide in some areas, is a preplant soil fumigant for the management of all major species of nematodes and certain nematode-transmitted diseases. As a fumigant, Telone moves throughout the soil profile on its own rather than requiring water or incorporation for movement.

Contact nematicides may appear to be an attractive option, but they may only prove effective under certain weather and field conditions. But in many cases, growers should apply a contact nematicide in conjunction with Telone to provide the best management possible.

The following product bulletins provide further information on the application of Telone II for nematode management in potato production:

  • "Sequential Application of Telone II plus K-PAM HL or Sectagon 42 or Vapam HL for Suppression of Verticillium dahliae, Control of Stubby-root Nematode Vector of Corky Ringspot and Control of Root-knot and Lesion Nematodes in Soils to be Planted to Potatoes, Onions and Carrots."
  • "For Control of Stubby-root Nematode Vector of Corky Ringspot in Soils to be Planted to Potatoes"
  • "Simultaneous Application of Telone II plus K-PAM HL or Sectagon 42 or Vapam HL for Suppression of Verticillium dahliae and Suppression of Root-knot, Lesion Nematodes and Stubby-root Nematode Vector of Corky Ringspot in Soils to be Planted to Potatoes, Onions and Carrots"

Telone® II soil fumigant has received two additional supplemental labels for the management of nematodes in the Pacific Northwest. In California (Modoc and Siskiyou counties), Colorado, Idaho, Nevada, Oregon, Utah and Washington, refer to the supplemental labeling for Telone II titled "For the Control of Nematodes and the Suppression of Wireworms in Soils to be Planted to Potatoes, Onions or Carrots" for directions for use.

Potato growers in Idaho also can refer to the supplemental labeling for TeloneII titled "For Treatment of Soils Actively Involved in the USDA/ISDA Potato Cyst Nematode Eradication Program" for directions for use.