Onion growing has changed in recent years, primarily due to improved hybrid seed varieties. In the past, growers had to seed in high volumes in order to achieve desired germination, and then cull as the plant grew. Today onions can be seeded at much lower rates, with seed treatments being used to help with emergence. There are three types of onions grown in Canada. Dry onions, such as Spanish onions, are the most common. Onion sets such as shallots are sown closer together for smaller bulbs. And bunching onions, such as scallions, are harvested before they form bulbs.
Manage disease in-season and post-harvest
Onions are susceptible to diseases both during the season and once they have been placed into storage for curing and drying. Botrytis attacks as leaf blight during the season and as neck rot while in storage. A pre-harvest fungicide, followed by harvest at maturity and prompt drying can keep botrytis away. Downey mildew can overwinter in the soil so it’s important to destroy cull piles and rotate away from susceptible crops. Purple blotch appears after downey mildew and botrytis and can cause high crop loss.
Manage grassy and broadleaf weeds throughout the season
Onions do not compete well against weeds. When weed pressure is high, the onions will emerge slowly and will lose out on early season growth. Shallow tillage is one way to prepare the soil for seeding. For fields with higher pressure of broadleaf and grassy weeds, a pre-emergent herbicide can help prepare the field for the season. A post-emergent herbicide can also be applied as necessary as the field should remain weed-free throughout the growing season.
Insect damage can reduce onion grade
Onion maggots are the most serious insect to an onion crop, especially to onion sets. While they also attack the roots, they are most damaging when they attack the bulbs. As eggs can overwinter in the soil, a good rotation can help keep numbers down. Onion thrips are primarily an issue in dry, hot weather. Thrips can be treated with an insecticide when the economic threshold is met. Cutworms are night feeders and can be hard to spot during the day, however their damage is easy to see. They can be treated with an insecticide when the larvae are small.