The increase of fungicide resistance is a major reason why SLB has recently become the dominant foliar pathogen in onions.
In New York state, onions are grown in areas sometimes referred to as muck lands – former swamps now filled with organically rich soil that boosts productivity.
Five years ago, however, onion growers started reporting large incidents of premature leaf death in their fields. It affected nearly 75% of growers’ crops and put a dent in the state’s onion industry, which has a four-year average value of $44.7 million, based on data from the U.S. Department of Agriculture.
Onions are at risk for many foliar diseases – such as Botrytis leaf blight, purple blotch and downy mildew – but this time, researchers identified the culprit as Stemphylium leaf blight (SLB), a relatively new and increasingly devastating disease.
“The short-term losses can be staggering,” said onion farmer Matt Mortellaro, co-owner of G. Mortellaro & Sons in Elba, New York. “It can result in a total crop failure if it takes hold in a field.”
A study from researchers at Cornell AgriTech in Geneva, New York, has identified better ways to manage SLB and use fungicide more effectively. “Emergence of Stemphylium Leaf Blight of Onion in New York Associated With Fungicide Resistance” published Nov. 21, 2019, in the journal Plant Disease.
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