Leek and Onion – Allium Problems

Leek Moth

Will not affect ornamental alliums
White or brown patches develop where leaves ahve been eaten by caterpillars.
Larvae bore into bulbs or stems causing secondary rots.
More prevalent near the coast where two generations in May and October can cause problems
No effective insecticide for home gardeners
Keep plants well watered in summer for strong growth
In severe cases grow under fleece

Affects onions garlic shallots but less severe on leeks.
Symptoms include yellow and wilting leaves
Roots rot and leave mould and black sclerotia in the soil which can survive to cause problems for 8 years
Plants become loose in the soil and start to go soft.
Most severe in cool wet summers
Transmitted by contaminated soil not airborne
Control by destroying affected plants before sclerotia form. There is no chemical control.
Avoid spreading contaminated soil on boots.