Leek moth. Photo by David Fuller
Leek moth larvae on the inside of an onion leaf. Photo by David Fuller
By Dave Fuller, Agriculture and Non-Timber Forest Products Professional, UMaine Cooperative Extension, Franklin County
Leek moth (Acrolepiopsis assectella Zeller), a very destructive pest of all of the Allium genus, was first found in Jackman, Maine, in the larval stage by the author on garlic plants at the Forest Hills Consolidated School garden on May 29, 2017.
Cooperative Extension in collaboration with Karen Coluzzi of the Maine Department of Agriculture, Conservation and Forestry, Division of Animal and Plant Health, initiated a detection trapping program in early June in multiple Maine locations. The object of the trapping was to determine where in Maine leek moths were found and to study its life cycle. The information would be used to alert growers of the presence of leek moth and to suggest ways to manage the pest. To date, Jackman is the only location in Maine where the moths have been found. Trapping will resume in the spring of 2018.
A native of Europe, leek moth first was seen in the United States in 2009 in New York and is now established in Vermont, New Hampshire and nearby in the Province of Quebec. Leek moth is so named for its affinity for leeks, but it is attracted to all members of the Allium genus.
Leek moth caterpillars (larvae) damage garlic and other allium leaves – sometimes extensively, leading to diminished crops or possible crop failure. So far damage on garlic in Maine has been seen mainly on the scape as it emerged, causing collapse of the structure. On onions, damage was more extensive with larvae tunneling into the hollow leaves and feeding on the inside surface, causing a windowpane appearance. Mature larvae then exit the leaf and enter the pupal stage by spinning a loose cocoon.
Leek moths have three generations in Maine, with damage to plants compounding as the season goes on and leek moth populations build. Each generation completes its life cycle in 30 to 50 days, depending on the environment. Moths, larvae and cocoons are all very small, measuring about three-eighths-inch long. Female moths lay from 100 to 200 eggs per generation over a two-week period starting in spring. Leek moths overwinter as adults or pupae in crop residue.
Covering allium crops with row cover is the best way to control leek moths. Since the moths fly only at night, growers can weed and remove garlic scapes during the day and then replace covers. Wire hoops need to be used with onions, as wind-flapped row cover would damage their tops. No pesticides currently are registered for leek moth in Maine. In other states, Bacillus thuringiensis (Bt) is used, but timing is very important to be effective.
For more information, see https://web.entomology.cornell.edu/shelton/leek-moth/docs/Leek_Moth_Final.pdf.
Additionally, UMaine Extension staff found and identified two new-to-Maine garlic diseases during the 2017 growing season: Anthracnose caused by Colletotrichum on garlic and rust on garlic. The significance of both of these diseases is not well understood at this time. We will continue in 2018 to observe the effects on crops.