How do I get good seed set and avoid problems in an onion seed crop?

Poor seed set in an onion seed crop usually comes from weak pollination or disease on the umbels. Onions need insect pollination, mainly bees, so a lack of bee activity badly cuts seed set, and you should avoid spraying insecticides during flowering and ideally encourage bee colonies near the plot. Stemphylium blight, purple blotch and thrips attack the flower stalks and umbels and shrivel the developing seed, so manage these following the label, but never spray insecticide during peak flowering when bees are working. Provide good nutrition and staking so the tall stalks do not lodge. Harvest umbels in stages as they mature. Confirm the disease and pollination management for your seed crop with your KVK.