Onion Cull Piles - Management is Essential

Over the past couple of weeks, there have been a few reports of onion cull piles growing in size in onion growing regions across southwestern Ontario. An onion cull pile, by definition, is a pile of onions comprised of graded out onions, partially rotted onions and onion waste.

The key to remember about cull piles is one creature's waste is another creature's treasure.

Cull piles, of any crop, can act as a great reservoir for diseases and insect pests. For example, in potatoes, cull management is critical as a mitigation measure against late blight. In onions, cull pile management is important in the control of onion maggot populations. In addition, now that Iris Yellow Spot Virus has been detected in Ontario, cull pile management will be a critical step in minimizing the green bridge between growing seasons.

Ways to minimize large onion cull piles include fall and winter spreading, and/or the burial of crop debris. One way to help minimize sprouting and growth of volunteers involves chopping of onion residue before spreading.

It's important to remember that onions are a biennial crop. Discarded bulbs can and will sprout and grow. One way to minimize the growth of volunteer onions in your cull piles is to chop up the onions. Unlike potatoes, onion pieces do not have the ability to regrow.

Field spreading is an option for dealing with cull onions in the fall and winter rather than a large pile at the edge of the field. The key to spreading is depth. Cull onions spread too deep will not allow for adequate freezing. So, piles should be no more than a foot deep. It's also important to think about where you're spreading your culls. Try not to spread culls in land that you plan on growing onions, or other alliums, in the next year or two.

Another option is field burying. Again, minimize the depth of the pile, and ensure at least a foot or two of soil cover over the onion debris.

At the end of the day, handling your onion waste in the right way now will help with insect and disease management next season.

If you grow onions or other alliums, check out the vegetable session at the upcoming OFVC Convention "Growing for the Future" in February 2008. There will be a talk on garlic, onions and other alliums.

This has been Jennifer Allen, Vegetable Crop Specialist with OMAFRA in Guelph.

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