What caused Patterson onions to rot from the top down?

November 29, 2022 Ask the Expert, Managing Insect, Diseases, and Animal Pests, Vegetables

Question:

Thrips ruined our Gladiolus entirely. The Patterson onions that were growing nearby looked healthy. We harvested the onions and placed them for storage in the cool cellar. Now it seems, 100% of the bulbs are rotting from the top down. The Ebenezers seem unaffected. What is the issue?

Answer:

Jonathan Foster, Community Education Assistant

I’m very sorry to hear about the trouble with your onions!

We can’t be completely certain without photos and sample analysis, but it sounds like you are probably dealing with an outbreak of botrytis onion neck rot, a disease that enters the plants primarily via foliage during the growing season and whose symptoms often don’t show up until the bulbs are all safely packed away in storage. At that point, they begin to rot, to the gardener’s lament. The thrips on your nearby gladiolus are unlikely to be the main vector, though if they were feeding on your onions, such damage can decrease overall plant health to the point that they are more susceptible to pathogens. You can find more information on managing thrips in this NC State Univ fact sheet.

Regarding the rot, you can find disease management advice in this fact sheet from Utah State Univ and this one from Ohio State, but you will largely be focused on crop rotation (if you have the space in your garden), complete disposal of dead plant material, and careful attention to drying the bulb necks at harvest. There are some chemical options available, as well. Regrettably, there aren’t really any neck rot-resistant cultivars or varieties of onions to switch to.

I wish I had happier news for you, but it sounds as though at least your Ebenezers should pull you through the disheartening loss of the Pattersons.