We’ve been seeing increasing issues with leek moth, an invasive pest of alliums (garlic, leeks, onions, etc.) over the past several seasons. Leek moth cause damage through their larvae feeding on host plants, while the adult moths cause no direct damage. On alliums with flat leaves (garlics, leeks) the larvae feeds on the tops and inside of the leaves, as well as bores into the center of the plant leaving noticeable frass. In alliums with hollow leaves (onions, chives) the larvae will feed internally, producing translucent areas on the leaf known as "windowing". Leaf damage by leek moth larvae will reduce yields in affected crops, but they can also directly damage marketable portions of the plant. In garlic larvae will regularly bore into scapes and occasionally bulbs, as well as the stalk in leeks, rendering them unmarketable.
Larval
feeding damage on garlic. Photo: Agriculture and Agri-Food Canada
Based on sampling performed in NS,
we’ve observed up to 3
flights or 2 generations of leek moth. Depending on the region, the first flight occurs in late April to mid-May when overwintering leek moth adults emerge (last
generation from previous year), typically corresponding to when temperatures
reach 9.5oC. The second flight is of 1st generation adults,
beginning in late June and continues through mid-July. The third flight is of
2nd generation adults beginning in late-July to early-August. These dates give
some general guidance as to when flights occur, but the best way to track leek
moth on your farm is by trapping.
Pheromone traps are commercially
available and allow you to determine if/when leek moths are active on your
farm. Leek moth monitoring should begin in mid-April using
commercially available pheromone traps, which attract adult males. Pheromone
traps consist of a white delta trap, sticky pad and pheromone lure. The delta
trap can be reused for multiple years, but the sticky pads should be checked
and replaced weekly and the pheromone lure replaced monthly. The
recommended number of traps is 1-2 traps per acre, and they should be placed at
the edge of the upwind side of the field at crop canopy height.
The adult leek moth is a small (5-7mm in length) brown moth
with a distinctive white triangle in middle of its wings when they are folded
at rest and can be identified with a hand lens. Weekly counts should be recorded to
determine when leek moth first appear and peak flight so management strategies
can be timed correctly. Allium crops can also be
scouted for feeding damage from leek moth larvae, but when damage has already
appeared, it may be too late to effectively implement some controls.
Adult leek moth. Photo: David Fuller, University of Maine
Extension.
One
of the most effective ways to control leek moth is by using row covers.
Research done in Ontario has found that row
covers were just as effective as pesticides in reducing leek moth damage. These
covers physically block leek moth adult females from laying eggs on the crop
preventing establishment. Row covers should be applied before the first leek
moth flight in the spring, so have row cover on by mid-April to achieve good
control. Row cover can then be removed after the leek
moths stop being found from trapping, but covering may need to resume if leek
moths appear again from later flights. Additionally, leek moths are only
active at night, so row cover can be removed during the day to perform work in
your alliums without risk of egg laying, as long as the row cover goes back on
before dusk.
There are also several conventional and
biological pesticide products, some of which are organic, registered for use
against leek moth on allium crops. Application of these insecticides is generally recommended 7-10 days following
peak flight, determined through trapping, which targets larvae when they have
newly hatched and are actively feeding. If
leek moth controls are implemented early and effectively against the initial
flight period, crop damage and populations can be significantly reduced as well
as the severity of subsequent flights.
For
more information on where to get trap supplies and specific controls or
pesticide products please contact Perennia’s Integrated Pest Management
specialist, Matthew Peill, mpeill@perennia.ca.
