Plants affected
Potato and tomato.
Symptoms
Basal leaves turn yellow and then brown in mid-summer, this
symptom gradually spreading up the stem and leading to early
die-back. Potatoes produce a crop of small tubers when early
dieback has occurred. Spherical objects, or cysts, up to 1mm
in diameter can be seen on the roots if the plants are carefully
dug up. These may be white, yellow or brown in colour, and
are the swollen bodies of the female eelworms. Each one contains
up to 600 eggs that can remain viable in the soil for many
years.
Cause
Golden cyst eelworm (Globodera rostochiensis) predominates in southern Britain while the white cyst eelworm (Globodera pallida) is more common north of Yorkshire and Lancashire, and also in much of Lincolnshire.
When the cysts first develop on the outside of the roots they are white in both species. Those of the white cyst eelworm then turn brown but those of the golden cyst eelworm go through a pale yellow phase before they also become brown.
Control
There is no chemical control available for the amateur gardener.
Rotate potato and tomato planting around different parts of the garden. Avoid returning to the same planting site for as many seasons as possible to delay a damaging build up of the pest.
Once soil has become heavily infested it may be seven or more years before it is worthwhile trying to grow potatoes again. Self-set potatoes should be removed or they will defeat the object of crop rotation.
Lift potatoes as soon as the tubers are ready to limit the increase in cyst numbers. Potato and tomato roots should be dried off and then burnt on the part of the garden where they grew.
Plants grown in infested soil should not be transplanted to cyst-free areas, and the roots, including those of weeds, should not be put on the compost heap.
Tomatoes can be raised in growing-bags which isolate the roots from the underlying infested soil and so prevent infestation.
Some potato cultivars are resistant to attack and some examples
of these are:
Earlies: ‘Accent’,
‘Lady Christl’, ‘Pentland Javelin’, ‘Premiere’,
‘Rocket’, ‘Swift', ‘Winston'
Second earlies:
'Cabaret', ‘Kestrel’, ‘Nadine’, ‘Saxon’
Maincrop: ‘Cara’,
‘Maris Piper’, ‘Maxine’, ‘Nicola’,
‘Picasso’, ‘Sante’, 'Spey', ‘Valor’
These all have resistance to the golden cyst nematode, but ‘Accord’, ‘Kestrel’, ‘Maxine’, ‘Sante’, 'Spey' and ‘Valor’ are also able to tolerate infestation by white cyst nematode and produce a worthwhile crop when grown as part of a crop rotation.
When taking over a garden or allotment where potatoes are to be grown, it is advisable to have the soil tested for the presence of cysts. This service is available to RHS members who should send or bring at least 250g (8oz) of dry soil to the RHS Members' Advisory Service at RHS Garden Wisley.
Andrew Halstead