Leek moth larvae can cause severe damage to your allium crops by tunnelling through them, creating both an unsalable crop and sites for secondary infection, which will further damage your onions, leeks, and garlic. Because the larvae spend most of their time inside of your plants, they are inherently difficult to deal with.
They do have an exploitable weak spot that you can use to dramatically
reduce their numbers and help to protect your crop from the larger waves of
leek moth that come with the second and, potentially, third waves we will get.
Before the leek moth can make its second flight (typically in early July), the larvae must leave the safety of the plant's interior and
create a cocoon on the leaf. They will stay in this cocoon for roughly
12 days before emerging as moths. This gives you, the grower, a twelve-day
window to control your populations by eradicating the cocoons (pictured below).
Photo: AAFC
If you miss this window, each emerging moth can lay between
100-200 eggs, which will hatch as larvae and immediately tunnel into your
allium crop--making control from that point on very challenging.
This twelve-day window is the most important period you will
have to control leek moth this year and it is likely to start in roughly a week, depending on where in the province you are located (southern areas will be slightly
ahead of northern areas).
When deciding where to scout for leek moth cocoons on your
property, think about what plants were growing during the first flight (early
June). Often there are no onions/shallots/leeks planted in the ground at that
time, so it’s not likely that you would find cocoons on them. Instead, focus on
crops that have overwintered. The crops you are most likely to find cocoons on
from the first flight are: Chives, Garlic, and plants in the Liliaceae
family.
Placing insect netting/row cover over your crops forms a protective barrier; however, if one of the plants already has a larvae/cocoon in/on it when you cover your crop, then row cover can create a protected area that will benefit emerging leek moths. It’s crucial to scout your crop before applying row cover.
Any time you can put into scouting your chives, garlic,
and lily family crops over the next couple of weeks will significantly reduce
their future populations.
Here is a great resource if you’d like to learn more: https://rvpadmin.cce.cornell.edu/uploads/doc_764.pdf
Good luck hunting!
Tim
