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Potato cyst nematode (Cysts)
Globodera rostochiensis or G. pallida
Potato cyst nematodes (PCN), causing major damage to potato crops, are two closely related species, which can occur together in many fields. G. rostochiensis ("yellow or golden" PCN) and G. pallida ("white" PCN) also exist as a number of different pathotypes.
Cysts are the remains of female nematodes and each contains around 200-500 eggs each with a larva inside. In the presence of potatoes, eggs are stimulated to hatch by root exudate and the larvae invade the roots damaging tissue and taking nutrients from the plant. As the female nematodes grow within the roots, they swell and their swollen bodies emerge through the root walls but their heads remain attached within the root. At this stage white or golden cysts may be seen on the roots, but once mature the females die and all cysts turn brown. When crops are harvested cysts detach and remain in the soil, but some may be spread on equipment to infest other fields. A small number of eggs hatch every year in the absence of a potato crop, but decline is variable and can take many years. Therefore, it is important to assess the risk prior to planting by taking soil samples.
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Control
Most potato varieties are susceptible to PCN. Resistance to G. rostochiensis (pathotype RO1) is present in a number of varieties e.g. Maris Piper, and some e.g. Sante, Nadine have resistance to G. rostochiensis and partial resistance to G. pallida (pathotype Pa2/3), but none are fully resistant to G. pallida. Use of a nematicide can help prevent an increase in PCN and increase yields.
For control of PCN on all soil types, apply Temik 10G as an overall treatment at 33.6 kg/ha (maincrop) or 22.4 kg/ha (first earlies, harvested within 8 weeks of planting) immediately before planting.
If low numbers (1-10 eggs/g soil) are found, use of Temik 10G will be worthwhile to reduce multiplication in close rotations. Yield benefits will also be seen, particularly if a susceptible variety is being grown.
Where moderate numbers (11-60 eggs/g) are present, use of Temik 10G is strongly recommended on all varieties. Growing a PCN tolerant and resistant may also be helpful. Final populations, even with use of Temik 10G will be high. Where hot spots occur, soil sterilisation should be considered.
Where high numbers of eggs occur (>60 eggs/g), the use of Temik 10G with a resistant variety may provide an economic return, but yields will still be affected and not reach full potential. An extended rotation will be necessary.
In all cases, timely fertiliser application and irrigation to limit crop stress will also be beneficial in giving the crop good conditions for optimal growth.
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