Simon’s Seasonal Insights – Crop Stress Raises Risk Of Disease Susceptibility In Onions

26 July 2025, UK: Onion crops have suffered severely from heat and drought stress this season. For many, irrigation resources are running dry. As we move into August, heavy dews and prolonged leaf wetness in cooler conditions will increase the risk of mildew developing in stressed plants.  

While downy mildew pressure has been low in the dry conditions, as day length shortens and periods of intense rainfall will almost inevitably occur, infection risks will occur. Irrigation can also increase disease risk.

When planning disease control for downy mildew (above), a golden rule is to ensure crops are sprayed weekly, and resist stretching intervals even in dry weather.  This will ensure newly emerging leaves are protected.  

Product choice with initial applications tends not to be as important, but once the canopy starts to thicken and bulb formation is under way, the most effective products should be targeted here.  Alternating ORONDIS® Plus + AMISTAR® with products like Unicur will give the strongest protection against disease at this critical stage

QUANTIS® helps crop resilience and maintain returns

Drilled crops such as onions, which are grown on light soils, are vulnerable during prolonged dry periods, making it almost impossible to maintain adequate soil moisture levels. This results in periods where the crop becomes drier than desired and inevitably stops growing, and even worse, experiences cell damage

QUANTIS^TM supports growth by acting as an osmoprotectant, keeping stomata open, sustaining photosynthesis, providing carbohydrates, and reducing oxidative damage.

Trials with QUANTIS^TM applied at 2 l/ha every 14 days from the five true leaf stage increased bulb size and yield, as shown below.

Also Read: India’s Biostimulant Sector Faces Regulatory Breakdown: BASAI Calls for Urgent Government Action

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