This brochure was created by Pete Nelson, a graduate student at North Carolina State University, who worked with the Kenya Plant Health Inspectorate Service (KEPHIS) on a 2017 Trellis Fund project focused on "Improving food production by adopting best pest management methods."
Potato cyst nematodes: A new threat to potatoes in Kenya
Symptoms of a potato cyst nematode infestation include:
- Stunted potato plants with yellowed or discolored leaves
- Wilted plants
- Plants with reduced root systems that are branched and brownish in color
- Potato plants whose roots have visible cysts or adult female nematodes attached to them
Effects of infection by potato cyst nematodes
- Damage can vary from small patches of poorly performing potato plants to complete crop failure depending upon nematode populations.
- In light infestations, plants may have no outwardly visible symptoms, but crop yield can be decreased.
- Heavy infestations result in decreased number and size of tubers and crop losses as high as eighty percent.
- Potatoes are vulnerable to pathogens such as R. solanacearum (the bacterial wilt pathogen) which can easily enter plant roots through wounds caused by the nematodes.
- Potato cyst nematodes decrease the sugar content and shelf life of potatoes. Infected potatoes have more brown spots than other potatoes.
Types and developmental stages of potato cyst nematodes
Potato cyst nematodes exist as two main species: Globodera rostochiensis and Globodera pallida.
They have five main development stages and grow from eggs to larvae/juveniles to adults and cysts.
The eggs, larvae/juveniles and adult males can only be viewed with a microscope while adult females and cysts can be seen with the naked eye. As a result, soil testing is the best way to detect the presence of nematodes.
Modes of potato cyst nematode transmission
Potato cyst nematodes are spread through infested seed potatoes and contaminated soil spread by potatoes, farm machinery, tools, boots, plants, runoff water or the wind. Once the nematodes are introduced to an area, they can survive for a long periods of time as cysts without a host plant.
11 practices to manage potato cyst nematode (PCN)
- Phytosanitary and quarantine regulation: Carry out regular surveillance and adhere to regulatory measures to minimize spread of PCN to non-infested areas.
- Use of high-quality seed: Plant certified seed from registered seed merchants or high-quality seed potato from reliable sources to avoid introducing PCN on land that might still be free of the pest or to avoid its increase.
- Field hygiene: Avoid the spread of potato cyst nematodes through infested or contaminated soils adhering to farm tools and footwear; washing with water and disinfecting (with 40% Kerol or other appropriate disinfectant) should be done when entering and leaving a potato field.
- Control water run-off: Dig trenches/cut off drains between and within plots to prevent the spread of PCN through runoff water.
- Roguing: Uproot severely affected plants and destroy them by burning or burying in deep pits.
- Crop rotation: Alternate planting of potatoes with nonsolanaceous crops (e.g. maize, beans, cabbages, carrots, wheat and peas) for a period of at least 7 years.
- Soil solarization: Plough the fields to fine tilth to expose nematodes to desiccation and solar heat during hot months. Covering the ploughed land with clear polythene sheets for about one month can improve solarization.
- Bio-fumigation: Plough or incorporate into the soil residues from crops in the Brassica family (e.g. kale, cabbage, Indian mustard) so that they decompose to release natural chemicals that kill nematodes.
- Trap cropping: Grow solanaceous plants such as potato, eggplant, tomato and black nightshade on land that has had heavy potato cyst nematodes infestation and destroy them when still young (5-6 weeks). Such plants trigger hatching of eggs into juveniles and development into young adults which get destroyed together with the plants through uprooting and subsequent burning or burying in deep pits.
- Chemical Control: apply pesticides to potato plants
- Use of resistant varieties: Resistant varieties are important in the management of potato cyst nematode, where available.