Leek moth poses threat for garlic, onion growers on P.E.I.

An invasive species that attacks leeks, garlic and onions could become a big problem on Prince Edward Island.

The leek moth is a tiny brown insect that likes to feed on a class of vegetables known as alliums, and it can cause a lot of damage.

Al Picketts, a garlic farmer in central P.E.I., said he is concerned the pest will wipe out his crops someday. 

"When they can find garlic, they just destroy the crop," he said. "So it's just going to be the end of you growing garlic."

Picketts said other farmers on the Island have dealt with the moth in recent years, and the pest has done a lot more damage to crops in other provinces. 

"The leek moth could be a major setback for growing garlic here — and how you get rid of it, I have no idea," he said.

The larval form of the moth will eat through the plant, preferring to feast on leeks and larger and healthier plants. Small exit holes may be spotted after the larvae grow into moths and fly away from the eaten-out part of the plant.

At that point, an adult moth no longer poses a threat to a plant. 

Picketts said the larvae can be identified by orange or red dots on their back, but they are very small and difficult to see. That can create problems when it's time to sell the garlic.

"I would expect a consumer might not be very happy if they open up a garlic bulb and find two or three big worms in there," he said. "Not only does it damage your crop, it damages your credibility. And there's not really any way you can prevent that... It's not something that you've done wrong, it's just that the worm has a way of infiltrating the bulb."

Picketts plans to spray a non-chemical product containing Bacillus thuringiensis (or B.t.) next spring to help keep the moth away. That type of bacteria produces a protein crystal that will kill the leek moth when it's still in the caterpillar stage. However, it can be expensive and washes away easily if there's rain shortly after it's been applied. 

Christine Noronha, a research scientist with Agriculture and Agri-Food Canada, said the leek moth has been on the Island for over a decade, but has done more damage in the last few years.

One reason could be the warmer spring and summer temperatures P.E.I. has been experiencing.   

"When you start to see temperatures go up, the number of generations can start to increase," she said. "Usually, it's just one generation. If it's a cool summer, you have one generation.