Allium Alert

Every fall, gardeners look forward to planting alliums: namely, garlic, shallot, and the many colorful varieties of flowering alliums, like Summer Drummer and Persian Star.

Unfortunately, in Oregon, our climate and soils are especially vulnerable to two invasive threats: Allium white rot and Allium leafminer.

Allium Leafminer

Allium leafminer

First detected in the U.S. in leeks growing in Lancaster, Pennsylvania in 2015, this small fly’s larvae tunnel through leaves and bulbs, killing plants or making them unmarketable.

Bulb onion infested with several allium leafminer pupae. Photo by Debbie Roos.

The Oregon Department of Agriculture has a quarantine prohibiting untreated Allium bulbs or plants from infested states unless they’re certified pest-free. That’s why we can’t import most ornamental allium bulbs sold by big national suppliers, as they often come from regions where leafminer is present.

Allium White Rot

Stromatinia cepivora spores, the tiny black "seeds" on decaying allium skin. UC IPM

Allium white rot is a soil-borne fungus that causes bulbs and roots to rot with a white, cottony mold. The spores can survive 20 years or more in the soil and spread through contaminated plant material, tools, or even a gardener’s shoes. Once it’s introduced, there’s no reliable cure, and entire plots may become unusable for alliums for decades. Because of this, Oregon law requires certified, inspected stock for allium seed, bulbs, and cloves intended for planting.

Grocery Store Garlic

If you’re planning to grow garlic, it’s important to know that even organic bulbs from grocery stores can carry white rot fungus. Garlic sold for planting is tested for disease and certified clean. It costs more, but it’s a one-time investment. You can save and replant your own bulbs every year. Protect your garden and your neighbors’ gardens by planting only certified seed garlic. The cheapest garlic isn’t the best deal if it ruins the soil for years to come.

East Portland Plant Buying Club Allium Sales

To stay compliant and protect our soils:

• We only source garlic and shallot bulbs from inspected farms in Washington State, where certification meets Oregon’s requirements.

• We don’t currently sell ornamental alliums, because most wholesale suppliers can’t guarantee pest-free certification for Oregon import. We will be working with more local growers next year.

• We encourage growers to save and replant their own garlic after their first certified purchase.

References:

• Oregon Department of Agriculture: Allium Leafminer Quarantine

• University of California Pest Management Guidelines: White Rot 

• Oregon State University Extension: Onion White Rot 

• University of Maryland Extension: Allium (Onion) Leafminer

• University of Maryland Extension: Allium Leaf Miner - Again - Really