Protect Spinach All Season Long

Expert Insights
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Spinach diseases are affecting field production and are causing leaf damages and imperfections which are decreasing the leaf quality and appearance. They also damage yield potential and decreases the overall product quality. Peronospora, downy mildew, and stemphylium are considered  as the most damaging spinach diseases. 

Other fungus can also affect spinach leaves like: white rust (Albugo), Colletotrichum (Anthracnosis) and Cladosporium. Not all of them are equally present all year long and every year.

“We work to find solutions for baby leaf, bunching, and processing markets,” said Yoann Barrier, Syngenta Vegetable Seeds Regional Portfolio Manager-Leafy. “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. That’s why researchers at Syngenta Vegetable Seeds are constantly on top of new races of diseases, testing varieties in growing conditions across 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 

 Whatever the disease, the imperfections caused by pests in spinach fields can hurt the plant’s ability to photo synthesize, decrease yield quality, and diminish overall yield potential. Discover how to differentiate the diseases: 

Peronospora symptoms include: 

  • Dull to bright yellow spots on leaves that can enlarge and become tan and dry over time. The underside of the leaf can reveal purple growth from the fungus and in more severe infections, leaves can curl and distort.  

Stemphylium is characterized by:  

  • Leaves with small circular to oval, gray-green spots. As the disease progresses, the spots enlarge (still keeping the circular to oval shape) and turn tan in color before drying out. This fungus does not showcase any purpling or other fungal growth because it is not a fungal infection. 


“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 strongly impact spinach production quality and in the worst cases destroy field production: growers just cannot afford this kind of risk. 

Finding combined disease resistant varieties with good agronomy and quality is getting more and more complex as new isolates continue to develop. It is a complex process that requires seed companies to constantly monitor and test to offer growers around the world the resistant varieties of tomorrow. 

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 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.

Just as Peronospora causes downy mildew in spinach, bremia causes downy mildew in lettuce. 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 is to understand how to protect crops from diseases and other yield-robbing pests.