20 January 2024, UK: Spinach diseases not only cause imperfections, they also damage a plant’s ability to photosynthesize, which hurts yield potential and decreases the overall product quality. Peronospora, or downy mildew, is often considered one of the most damaging spinach diseases. Recent testing has also shown Stemphylium to be a rising threat to spinach growers.
“We work to find solutions for baby leaf, bunching, and processing markets,” said Yoann Barrier, Syngenta Vegetable Seeds Regional Portfolio Manager-Leafy and Brassica. “This is to help growers have varieties with extremely nice performance in the field and also that have the highest resistance package we can provide against disease.”
There are fewer in-season controls available to combat these diseases. That’s why researchers at Syngenta Vegetable Seeds stay ahead of new races of diseases by testing varieties in growing conditions around the globe. As new races of pests and disease emerge, disease resistant spinach varieties from Syngenta Vegetable Seeds are updated just as frequently to give growers the protection they need.
In addition to planting resistant varieties, understanding the conditions for development and identifying these diseases are the best ways to prevent yield loss.
Conditions for Development and Spread of Peronospora and Stemphylium
All downy mildews require certain conditions for development, as reported by the University of California. First, cool, wet conditions are key for Peronospora – downy mildew – development. Additionally, densely planted fields, especially those with heavy canopies for moisture retention are at risk. Peronospora is spread from field to field through the wind and water splashing.
“Downy mildew is one of those traits where not having a resistance trait just isn’t an option,” said Michel de Lange, Syngenta Vegetable Seeds Trait Development Lead. “It can completely destroy yields and growers just can’t afford to take that kind of risk.”
Most damage from Stemphylium occurs in humid conditions, according to Utah State University. It is both windborne and seedborne. Stemphylium can be spread as spores from volunteer spinach are splashed onto new plants.
Finding new resistant varieties as the races of disease continue to develop is a complex process that requires constant monitoring and testing.
How to Identify Peronospora and Stemphylium
Monitor plants for symptoms of downy mildew at least once a week, according to Cornell University. Look for signs of an initial infection, which will appear as dull to bright yellow spots on cotyledons. It’s best to check in the early morning, and monitor leaves of all ages.
Over time, spots will get larger, dry out, and turn tan. Inspect the underside of leaves for a purple fungus growth. It’s also important to monitory for multiple infection sites of extensive disease development which may lead to curled leaves and a potential for blight.
The symptoms of Stemphylium may resemble tan spots caused by pesticide or fertilizer damage, says the University of California. The initial symptoms will appear as 0.13 to 0.25 inch diameter circular or oval grey-green spots. Disease progression will enlarge the spots and turn them tan. Older spots will become papery and dry up. Stemphylium can be differentiated from other fungal diseases due to its lack of purple growth like in downy mildew or green spores like in Cladosporium leaf spot.
Keeping up with the latest evolutions of these diseases across a variety of crops in a multitude of growing conditions is how Syngenta Vegetable Seeds continues to provide innovations that matter to growers.
Stay up to date on the latest innovations in leafy vegetables here to understand how to protect crops from diseases and other yield-robbing pests.
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