🐛✗ Tested and false“You only need to net leeks once you spot the first signs of moth damage”
Mesh works by physically stopping the adult moth from reaching the crop to lay eggs; once caterpillars are already mining the leaves, a barrier over the top does nothing to remove them. The RHS guidance is to keep insect-proof mesh in place for the entire growing season, not to add it reactively once damage appears. Nova Scotia's provincial horticulture extension gives the same instruction for row covers, recommending they go on before the first spring flight of adults and stay on, only lifting them briefly for fieldwork.
Our read Both sources treat mesh as prevention against egg-laying, not as a treatment for an active infestation, which is the opposite of how the myth frames it.
What to do: Put mesh over leeks, onions and garlic before growth starts in spring and leave it on for the whole season, weighing or pegging the edges down so moths cannot walk in underneath.
In Scotland: Leek moth is mainly established in southern England with a northward spread and no confirmed Scottish range yet, so this is worth doing as good practice rather than a response to a confirmed local outbreak.
2 sources
“Leek moth only attacks leeks, so onions, garlic and shallots are safe from it”
Leek moth caterpillars feed across the allium family, not just on leeks. The RHS lists onion, shallot and garlic alongside leek as affected crops, and University of Vermont Extension separately confirms leek moth populations found in onions and garlic as well as leeks, with chives also named as a host. A bed of onions or garlic sitting next to netted leeks is not automatically protected just because the netting was aimed at the leeks.
Our read Two independent sources, one UK and one North American, list the same wider allium host range, which is a stronger basis than either alone.
What to do: Cover onions, garlic and shallots with the same insect-proof mesh used for leeks, not just the leek bed, and rotate all alliums together rather than treating leeks as the only crop at risk.
2 sources
“Putting out pheromone traps will trap enough leek moths to control the infestation”
Pheromone traps for leek moth are built and marketed as a monitoring tool: a lure draws in adult males so a grower can see when moths are flying and time other controls accordingly. University of Vermont Extension frames trap catches purely as a trigger for timing pesticide applications, not as a way of removing enough moths to bring numbers down on their own. Perennia's Nova Scotia extension programme is explicit that its traps are for monitoring only, used to record weekly counts and identify peak flight periods rather than to suppress the population directly.
Our read Neither source claims mass-trapping meaningfully reduces leek moth numbers; both use the traps to decide when to act, not as the action itself.
What to do: Use a pheromone trap to find out when moths are flying in your garden and time mesh installation or hand-picking around that, rather than relying on the trap itself to bring numbers down.
2 sources
