In eastern Canada, Botrytis Leaf Blight (BLB) of onions caused by the fungus Botrytis squamosa is the key disease for scheduling fungicide applications. BLB is characterized by silver halos on green leaves, followed by leaf tip dieback and leaf blighting, which reduces photosynthesis and consequently bulb size. Although there are some onion cultivars that are tolerant to the disease, they are not widely-planted in Canada because they are not suitable for long-term storage.
“There are no commercially available onion cultivars that are resistant to B. squamosa. However, a few of the early cultivars are known to be tolerant. These cultivars can produce a marketable yield under wet weather conditions and are grown on both conventional farms and organic certified farms for which there are no registered fungicides that are effective against BLB. However, these cultivars are not suitable for long-term storage; hence, they represent only a small part of the total onion acreage in northern climates. Consequently, in most onion production areas where BLB is a problem, the disease is managed through repeated applications of fungicides on a regular calendar-based schedule or following a leaf blight predictive system. Typical fungicide spray programs involve applying fungicides every seven to ten days from the four-leaf growth stage until sprout inhibitor application or 50% soft neck stage.”
Author: Herve Van der Heyden, et al
Affiliation: Compagnie de recherché Phytodata Inc. Quebec, Canada
Title: Comparison of monitoring based indicators for initiating fungicide spray programs to control Botrytis leaf blight of onion
Source: Crop Protection. March 2012. 33:21-28.