Be Aware of Leek Moth - A Pest of Allium Crops

The leek moth (Acrolepiopsis assectella Zeller) is an invasive alien species of European origin that damages Allium spp. including garlic, onions and leeks (Figure 1). Since its detection in 1993 in the Ottawa region, the leek moth has caused significant damage to both commercial and organic market garden producers in eastern Ontario and southwestern Quebec.

Figure 1. Leek moth adult (left), larva (center), pupa (right). (Adult leek moth photo source: Jean-François Landry, AAFC.) Adult leek moth is a small, reddish-brown moth with a white triangular mark on the middle of its folded wings. Larvae are greenish yellow with a pale brown head and 8 small gray spots on each abdominal segment. Pupae are reddish brown encased in a cocoon.

Photo of a leek moth adult, larva, pupa.  Adult leek moth is a small, reddish-brown moth with a white triangular mark on the middle of its folded wings. Larvae are greenish yellow with a pale brown head and 8 small gray spots on each abdominal segment. Pupae are reddish brown encased in a cocoon.

The larva are destructive by feeding on tissues of allium plants, see Figure. 2 for damage on various allium crops.To monitor for the presence and activity of leek moth, pheromone traps should be placed in allium plantings beginning in mid to late April, if possible. Entrust 80 W (organic formulation of spinosad) is currently registered on crop group 3-07B, including Green Onions, Leeks, Chives (fresh leaves), Chinese Chives (fresh leaves), Shallots (fresh leaves), Wild Leek, Bunching Onion (Beltsville bunching onion), Tree Onion (note: this does not include the crops in crop group 3-07A - i.e. dry bulb onions, garlic, shallots) to suppress leek moth, when applied 7 days after peak leek moth flight. Please consult with your certification body before using and refer to label for directions for use.

Figure 2. Leek moth feeding damage on garlic, leek, and onion. The larva tunnel and mine into the leafy tissue and occasionally bulbs. On onion, damage typically appears as 'windowing', because the larvae feed from inside the leaf.

A leek moth feeding damage on garlic, leek, and onion. The larva tunnel and mine into the leafy tissue and occasionally bulbs. On onion, damage typically appears as 'windowing', because the larvae feed from inside the leaf.

Cultural control methods include crop rotation away from alliums, avoiding planting near infested areas, delayed planting, removal of old/infested leaves, early harvesting to avoid damage by populations that have been building up through the season, and destruction of plant debris, which may contain leek moth. Research has also shown that the use of a lightweight floating row cover can protect plants from leek moth damage. Ensure the sides of cover are anchored to ground to prevent leek moth from entering the enclosure. The covers can be removed to perform tasks like garlic scaping and weeding during the day, as long as the covers are replaced before dusk. For more information on control methods please see: http://www.omafra.gov.on.ca/english/crops/facts/08-009.htm

In 2011, a survey was conducted to determine the distribution of leek moth in allium growing regions in southwestern Ontario. Pheromone traps were installed in dry bulb onions, leeks, wild leeks, garlic and green onions in 12 locations including, Prince Edward County, Northumberland County, Peterborough, Durham Region, Simcoe County, York Region, Hamilton-Wentworth, Waterloo Region, Wellington County, Norfolk County and Lambton County. Leek moth were captured at 3 of the 12 locations monitored, including 2 sites in Central Ontario, Simcoe County and York Region, and one site in southwestern Ontario in Waterloo Region (Figure 3). This work confirms the spread of leek moth into southwestern Ontario, thus it is important for allium growers in this region, particularly those that grow organically, to be aware of this pest by looking for damage or larva in their crops.

Figure 3. Map of counties in Southern Ontario where leek moth have been positively identified before 2007 through to 2011.

A map of counties in Southern Ontario where leek moth have been positively identified before 2007 through to 2011.

For more information on leek moth and management options, please see:
http://www.omafra.gov.on.ca/IPM/english/onions/insects/leek-moth.html#beginner
http://onvegetables.com/2011/07/27/leek-moth-update/ http://www.omafra.gov.on.ca/english/crops/facts/08-009.htm


For more information:
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E-mail: ag.info.omafra@ontario.ca