Onions are usually the “tough guys” of the vegetable patch, but even these hardy bulbs have their bad days. Unfortunately, a few specific pests and diseases love onions just as much as we do. If you want to keep your harvest healthy, here’s what you need to keep an eye out for.
Downy Mildew
If you’ve been gardening for a while, you’ve probably run into Downy Mildew. In the onion world, this is caused by a fungus called *Peronospora destructor*. This fungus thrives in cool, damp weather—basically, it’s looking for any excuse to multiply when things get soggy. It often hitches a ride on onions that have overwintered in the ground, and once spring rolls around, the wind carries the spores right to your new plants.
You’ll recognize this one by a fuzzy, violet-gray discoloration on the leaves. It’s actually pretty easy to miss at first, which is why it can spread so quickly. Eventually, the leaves turn a pale gray and start to die off. You’ll usually start seeing signs in May, especially if you’re having cool summer nights with lots of dew. A bad infestation won’t just shrink your harvest; it’ll also make your onions rot much faster in storage.
Luckily, you can fight back with a few simple steps:
- Choose resistant varieties when buying your seeds.
- Water in the morning or early afternoon so the plants aren’t sitting damp all night.
- Pick a breezy spot for your onion bed to help them dry out.
- Give your plants plenty of elbow room (spacing is key!).
- You can also try various organic home remedies to keep the fungus at bay.
The Onion Fly
The Onion Fly (or more specifically, its hungry larvae) is another major headache. Starting in April, these pests lay their eggs right at the base of the onions. Once the maggots hatch, they burrow straight into the bulb for a snack. Young plants are especially vulnerable since they haven’t toughened up yet. To make matters worse, these flies can hatch two or three times a year.
Keep an eye out for wilting plants with yellowing, dried-up tops. If the bulbs start to rot and you can pull them out of the soil with almost zero effort, you’ve likely got an onion fly problem. To protect your crop—especially between April and June—fine mesh netting is your best friend. It’s also a great idea to plant carrots nearby, as they act as a natural deterrent. Lastly, be careful not to overdo it with organic fertilizers, as the scent can actually attract the flies.