Case: Yield loss due to downy mildew in onions

increasing challenges in crop protection

Several crop protection products have disappeared in recent years, and it is possible that more will disappear in the coming years. This means farmers have fewer and fewer tools at their disposal to control diseases, pests and weeds. This situation has major implications for the control of weeds, insects such as the onion fly and fungi such as Downy Mildew. The end result is that the onion crop will be further plagued by various threats, which can lead to reduced crop growth and a possible decrease in yields per acre.

Downy Mildew

One of the most dangerous onion diseases is downy mildew. This fungal disease strikes mainly when humidity is high, especially when it exceeds 95%. In a season with regular precipitation and colder nights, resulting in morning dew and high humidity, Downy Mildew can strike hard. In contrast, too long leaf wet period, during which a film layer forms over the leaf, can make it more difficult for the fungus to penetrate the leaf.

The importance of timely protective measures
One of the challenges in controlling Downy Mildew is that once in the plant, the fungus cannot be controlled. Unfortunately, there are no remedies available to effectively control the fungus after it has emerged. Therefore, it is crucial to start preventive measures in a timely manner. Downy mildew has an incubation period of about 10 to 19 days, with the first spots on the onion leaf becoming visible on average after 14 days. Starting preventive remedies early is therefore essential to control the fungus before it can do damage.

Stefan van Heist, onion specialist at Bayer, stresses the importance of plot-specific data via weather poles: “If you want to predict disease more broadly and accurately, you need to measure relative humidity, leaf wet period and temperature on each plot.” It can be seen that smart systems that collect and process this data are becoming more important.

Protecting onions against downy mildew is an ongoing challenge for Dutch onion cultivation. The disappearance of effective plant protection products calls for new strategies and preventive measures to protect the crop from this fungal disease. Timely preventive treatment is with available crop protection products, such as Zorvec Endavia and Fandango is essential. However, the onion industry will need to continue to innovate and adapt to meet the growing challenges in crop protection and ensure onion quality and yields.

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