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Damage, Monitoring and Detection

The leek moth larva is a small, leaf-mining caterpillar. The first generation (May-June) feeds on the leaves. The worst damage is done by the second generation (July-August) as it continues to damage emerging leaves (Figure 1) and moves towards the bulb. Feeding damage stunts plant growth, introduces rot and can compromise the storage life of onions and garlic. In New York leek moth populations have been found in onions, garlic and leeks.

leek moth damage
Figure 1. Damage to leeks. Photo: Lorraine Chilson.

Where to look on various crops

On crops with hollow leaves (onions, shallots and chives), the larvae feed on the inside tissue, leaving characteristic ‘windowpane’ damage to the leaves (Figure 2 & 3). Split open damaged leaves and look for frass (excrement) and debris (Figure 4). Even after the larvae have left to pupate, the telltale debris remains visible (Figure 5).

leek moth damage on onions
Figure 2: Typical windowpane damage on Onion. Photo: Amy Ivy, Cornell University.
leek moth damage on shallots
Figure 3: Typical damage on shallots. Photo: Amy Ivy, Cornell University.
leek moth damage to onions
Figure 4: Onion leaf split open, larva and debris visible. Photo: Amy Ivy, Cornell University.
leek moth damage to garlic
Figure 5: Telltale debris. Photo: Amy Ivy, Cornell University.

On garlic and leeks, larvae feed on the leaf surfaces and sometimes tunnel through the leaves (Figure 6). They are often found in the protection of the folded leaves on leeks and garlic (Figure 7). In June in hardneck garlic, damage will be the most noticeable on the garlic scapes (Figure 8). On both crops check the newest leaves as well (Figure 9).

leek moth damage to leeks
Figure 6: Damage to leeks.
leek moth damage to garlic
Figure 7: Damage to garlic inside fold of leaf. Photo: Amy Ivy, Cornell University.
leek moth damage to garlic
Figure 8: Damage to garlic leaf and scape. Photo: Amy Ivy, Cornell University.
leek moth damage to garlic scape
Figure 8a: Damage to garlic scape. Photo: Scott Lewins, UVM.
leek moth damage to leek
Figure 9: Leek - Check newest leaves for damage.