Leek moth, also known as the Onion leaf-miner, is a pest of the Allium family which consists of onions, garlic, leeks, chives, and shallots. This European native was first found in Plattsburg, NY in the summer of 2009. The preferred hosts are leeks and onions, and it causes damage to the leaves and sometimes the bulb. Its main sources of damage are along perimeters of crop fields.
Leek moth causes damage to the leaves through larval feeding. Larvae begin feeding on the outside tissue of the leaves and as they develop begin to tunnel into the leaves, casing characteristic ‘windowpane’ damage. The moth is a potential threat to the US onion and leek production, specifically in the Great Lakes, Oregon, California, Texas, Colorado, Washington, Georgia, and New York. The insect causes premature aging of the plants along with rotting of plant tissue, reducing crop yield.
If you see whitish dead patches or streaks running down the leaves lengthwise, check for the larvae. Do this by splitting open the damaged onions and look for larvae.
Leek months are found living on plants in the leek family in northern regions of NY.
Identification of Leek Moth Adults:
Wings: speckled brown, white, and black with a distinctive white spot halfway down the outer pair of wings. The spot is usually round or triangular. The hind wings are light gray.
Size: They are approximately 3/8th of an inch long. The wingspan ranges from 11 to 15 mm.
Biology: These moths are nocturnal. The female, who can only reproduce once, can lay about 100 eggs. Males can stay alive for 23 days. The moth overwinters in this state in plant debris.
Identification of Leek Moth Larvae:
Appearance: Slender and creamy yellow
Size: 1-12 mm (less than ½ inch)
Location: on or in leaves
Larvae on Leaves of Leek Plant
Leek Moth Eggs on Leek Plant
Biology: First generation occurs in May-June. The second generation in July-August does the most damage by feeding on the bulb of the plant. It stunts the plant growth, introduces rot, and compromises storage for the plants. There are typically two to three generations per year, but some cases have shown up to 6 generations. It takes one week for eggs to hatch and two weeks for the larvae to pupate.
Identification of Leek Moth Pupae:
Appearance: A reddish-brown cocoon with a net-like structure over it.
Size: 1/3 inch
Location: Usually attached to dying foliage in the crown, but occasionally in the soil, on another plant, or in plant debris.
Biology: It takes 10 days for adults to emerge after pupation.
Control and Management:
One way to control leek moth is by sanitizing the affected area. This can be done by burning the debris, feeding the hosts to animals, controlling weeds, and bagging and burying the host material at a landfill. Make sure to check and clean vehicles for host debris and the insects themselves. Other cultural controls include crop rotation, flooding, barriers, fertilizing, pheromones, lures, and deterrent cropping. Fertilizing the crops aids in their response to damage and recovery time. This allows them to better adjust and grow after larval feeding. Planting a large amount of tomato plants with leeks has shown to be effective in deterring the insects. When larvae are found you can also crush them to prevent pupation.
Insecticides, when used in combination with other controls, can help remove the insects. Insecticides should be sprayed immediately upon discovery of the leek moth and during the late afternoon, evening, or night, since it is nocturnal. To avoid resistance rotate which insecticides you will use.
Bt (Bacillus thuringiensis) has shown to be effective in sensitive or urban areas. When using Bt make sure to get the leek moth biotype.
Neem Kernel antifeedant is used in biologically sensitive or urban areas. This can be used after pesticide applications, but should not be used with Bt treatments, as it inhibits the bacteria. This also should not be used in large populations since it can cause larvae to migrate.
Two parasitoids, Diadromus pulchellus (used in Canada) and Conura albifrons (a North American native used in New York), have shown to be effective in controlling populations.
Title photo: Jean-Francois Landry (omafra.gov.on.ca). Leek moth life stage photo:(agr.wa.gov). Habitat/Distribution map photo: (web.entomology.cornell.edu). Adult leek moth identification photo: Robin Barfoot (ukmoths.org.uk). Leek moth larvae photo: Mariusz Sobieski (bugwood.org). Egg stage photo:Dan Olmstead (web.entomology.cornell.edu). Pupae stage photo:Pupae stage of leek mouth: Steve Bennett (ukmoths.org.uk)
Ellis, Susan E. “New Pest Responses Guidelines Leek Moth.” New Pest Response Guidelines:Leek Moth (n.d.): n. pag. USDA APHIS PPQ PDMP, 25 Nov. 2004. Web. 28 July 2015. <http://www.aphis.usda.gov/import_export/plants/manuals/emergency/downloads/nprg_l eek_moth.pdf>.
Ivy, Amy. “Leek Moth 2010 Update.” Leek Moth 2010 Update (n.d.): n. pag. Leek Moth 2010Update. Cornell Cooperative Extension, 18 June 2010. Web. 28 July 2015. <http://www.cce.cornell.edu/Ag/Horticulture/Documents/Leek%20Moth%20Fact%20Sh eet%20Ivy%2006%2018%2010.pdf>.
“Leek Moth: Control.” Leek Moth: Control. Cornell University, n.d. Web. 30 July 2015. <http://web.entomology.cornell.edu/shelton/leek-moth/control.html>