ANNE SWITHINBANK’S MASTERCLASS
How to stop slugs eating your spuds!
QI lifted my maincrop potatoes only to find that the tubers were riddled with slug holes. How can I stop this happening next time? Sid Hasslebury, Brentwood
AThis is a complaint that’s familiar to most potato growers. The fork goes in and there is the usual rush of excitement when pale (or rosy-skinned) spuds show against the dark soil. And at first, they look great.
Slug damage is often invisible until the tubers are washed prior to cooking but then small entry holes show up, which cut through, reveal the tunnelling activities of small slugs and often the culprits themselves.
These are subterranean long-keeled slugs, whose underground activities place them safely out of reach of slug pellets, even if you wanted to use them. Damage to tubers you wish to store is a problem because they begin to rot, and this spreads to the sound ones.
Nematodes (Nemaslug) made into a solution and watered into soil enters the slugs and releases a bacteria which kills them. While potentially an effective way of reducing the slug population, they are living organisms and require moist soil to operate.
During dry spells, potatoes draw most of the moisture from the soil and I find it almost impossible to keep potatoes sufficiently irrigated for the nematodes to keep going.
Potato varieties are divided into early, second-early and maincrop according to when they mature. Slug damage is at its height from August into the autumn, so earlies and second-earlies planted in March and harvested from June onwards usually escape slug damage and blight.
Maincrop varieties mature in September and October and are more vulnerable. Sound second-earlies will store well, so there is an argument for growing more of these and harvesting them promptly before the slugs get going.
Should you suspect your potatoes have a slug problem, I recommend choosing a dry day to wash the tubers gently in a plastic wheelbarrow before drying them out on a soft lawn. Slug holes are then visible, making it possible to separate out the damaged ones.