This article appears in the April 2018 issue of Potato Grower.
Late blight is a never-ending potato disease challenge for growers. A preventative fungicide program that includes broad-spectrum fungicides combined with timely sprays of late blight-specific products greatly reduces the chances of late blight epidemics.
A two-year research project (2016-17) was conducted in Ontario to determine if passive spore traps would provide an early warning of late blight to better time late blight-specific fungicides.
The results indicated that passive spore traps placed in commercial potato fields proved to be a reliable method for detecting spores of the late blight pathogen (Phytophthora infestans) at least 15 days before lesions were detected in the field. The traps do not need a source of energy; they are activated by the wind. Filters held in the spore traps retain spores blowing in the air. The filters are changed twice a week and sent to a laboratory where a PCR-based test is used to detect P. infestans DNA. A positive PCR test indicates the presence of spores in the area. This information alerts growers of the increased risk of late blight and the need to tank-mix late blight-specific fungicides with broad-spectrum fungicides.
Spore Trap Placement
Spore traps are placed as close to the crop as possible at edges of fields before crop emergence. Windy areas near fields where late blight has been found in the past are the best locations. The traps should not interfere with farm equipment. In this project, two spore traps were installed per field.
Monitoring Traps
The filters were changed twice a week, usually on Mondays and Thursdays, and then sent to a laboratory that conducted the PCR tests. The laboratory provided the results within four hours.
Communication of PCR
Test results were emailed or texted to growers. Alerts were sent whenever the tests were positive. Spores were detected 15 days on average before late blight lesions were seen in a few fields. 2017 was the wettest summer on record in Ontario, but the incidence of late blight was low.
Once spores were detected, growers shortened spray intervals and switched to late blight-specific fungicides (always tank-mixed with a broad-spectrum product). This avoided an epidemic of late blight.
Healthy seed, protectant fungicide sprays before rows closure, the elimination of cull piles and volunteers, and field scouting also continue to be important components of a late blight strategy that uses spore traps.
The passive spore traps used in this study were provided by Sporometrics, a biotech company based in Toronto. Sporometrics calls these traps “Spornados.”
With the growing season approaching, Sporometrics is once again partnering with researcher Eugenia Banks—with support of the Ontario Potato Board, as well as two other groups of Ontario-based agricultural researchers—to tackle potato late blight in fields across Ontario. The use of these spore traps combined with PCR analysis technology the past three growing seasons has proven to be an invaluable tool as early predictors of late blight disease for growers. This year, for the first time, the Spornado is being used to monitor tomato and blueberry crops.