aLast summer, a Plattsburgh home gardener contacted Cornell Cooperative Extension regarding an insect problem in garlic. Surprisingly, the insect was identified by the USDA as leek moth (Acrolepiopsis assectella). This is the first report of this insect in the continental United States.
Since the first report of leek moth, this pest has been reported in several other Plattsburgh area gardens both last year and this year. While most insects stay away from onions and garlic, leek moth is a known pest of all Allium crops, including leek, onion, chives, green onion, shallot, garlic, elephant garlic, etc. and is considered a serious pest of these crops. The leek moth is native to Europe but can now be found in Asia, Africa, and North America. The first North American find of leek moth occurred in 1993 in Ontario Canada.
While leeks are the preferred host, all Allium crops will be attacked. The larvae (or caterpillars) cause significant damage to onions by tunneling mines into the leaf tissue causing distortion, stunted growth, and secondary bacterial and fungal infections. While most of the feeding occurs in the leaves, feeding occasionally occurs in the bulbs. Flowers are avoided since Allium flowers contain saponin, a compound that inhibits the growth of insects.
The adults moths are small ( approximately 1/2 inch wingspan; 1/4 inch long with wings folded at rest) reddish-brown moths with a white triangular mark on the middle of their folded wings. The hindwings of the moths are heavily fringed and are pale to dark grey in color. Adults are active at nightfall and right before dawn. Eggs are laid in the spring on leaf surfaces. The small yellowish-green caterpillars eat any cultivated onion-type plant prior to pupating in a reddishbrown netted cocoon. Most cocoons are found on the leaves but they can also be found on decaying plant matter near the crops.
If you grow any of the listed Alliums in your garden, inspect them for damage. Look for mined holes and windows in the leaves, small caterpillars, the caterpillars droppings (frass), cocoons, or adult moths.
If you suspect leek moth damage, it is probably best to destroy the plants. It is hard to use pesticides on these insects since they are often found inside the plant. If you do not have damage, a simple row cover can prevent infestation. Infected plants can be harvested and eaten but any portion of the plant not eaten must be burned or bagged and sent to the landfill in order to prevent the spread of this non native insect.
Anne Lenox Barlow has had experience in the agricultural field as a horticulture educator with Cornell Cooperative Extension in Clinton County. She can be reached by e-mail at firstname.lastname@example.org.