Plants affected
Potato and other root vegetables.
Symptoms
Holes in potato tubers can be caused by several pests but
the most frequent are keeled slugs (Milax
species). These make round holes in the skin, but much more
extensive cavities inside the tubers. Often by the time the
potatoes are lifted the slugs have gone back into the soil.
Biology
Keeled slugs can feed above ground but they live and feed mainly in the soil. They feed on decaying organic matter, as well as living plant material. Damage to potato tubers takes place from late summer to autumn.
Slug-damaged tubers are prone to secondary rots and should not be stored with sound tubers.
Control
Limit slug damage by lifting potatoes once the tubers have matured.
Some potato cultivars, such as 'Pentland Dell', 'Wilja', 'Charlotte', 'Golden Wonder', 'Estima', 'Sante' and 'Pentland Ivory' are less susceptible but none is fully resistant.
Soil-dwelling slugs can be controlled by using the pathogenic nematode, Phasmarhabditis hermaphrodita, which is available by mail order from suppliers of biological controls. It should be applied in the evening to moist soil after the potatoes have begun growth but before the top growth is too dense to allow access between the rows.
Andrew Halstead