b'Better Sooner Than LaterResearchers are working on innovative ways for growers to detect late blight before symptoms appear in their potato crops.BY:CAROLYN KINGLATE BLIGHT IS A deadly disease that requires integrated management, including foliar fungicides as a key tool. Usually potato growers make repeated preventive applications of broad-spectrum fungicides starting before row closure,These passive spore traps have and then use late blight-specific fungicides if the disease is found in their fields.proven to be accurate predictors Now studies in Ontario and the Maritimes are working on easy-to-use technologies for early detection of late blight that could allow more targeted fungicide strategies.of the presence of late blight Late blight is caused by Phytophthora infestans, a fungus-like organism.spores in a potato production area. It can spread by wind-blown spores, infected seed tubers and infected tomato transplants. The pathogen has the potential to infect a crop as early as emergenceThis allows growers to time the and throughout the rest of the season. Under conditions that favour the disease,application of late blight-specific late blight can spread rapidly, going from a single infected plant to an epidemic.fungicides. It can kill an entire potato plant within a few days of the appearance of visible symptoms, and it can destroy tubers in storage.EUGENIA BANKSThe early detection technologies being developed in these studies have the potential to help growers fine-tune their fungicide applications, reduce their fun-gicide costs, decrease the risk of fungicide resistance developing in the pathogen, and enhance control of this devastating disease.tions on the same day it received the filters. Growers were alerted if late blight spores were detected in their areas.EARLY WARNING WITH SPORE TRAPPING Banks evaluated such factors as the location and height placement of the Eugenia Banks, a potato specialist for the Ontario Potato Board, has beentraps; biweekly retrieval of filters to be analyzed in the lab; intensive field scouting developing and evaluating a simple-to-use spore trapping system. The idea of thisto double-check for the presence of a late blight outbreak; and the response of approach is to detect the spores before the disease begins attacking the crop.potato growers to detection of late blight spores in their region. In 2016 and 2017, Banks evaluated this spore trapping system in two OntarioAccording to Banks, the Spornado traps had previously been evaluated in potato production regions: the Alliston and Shelburne-Melancton areas. In 2018,another province with mixed results. However, in that earlier study, the traps had she added the Simcoe-Delhi and Leamington areas to the three-year project. Also,been placed about 2.5 metres above the ground, which she thought was too high. potato growers in the Sudbury area installed two spore traps in their region. For theThe spores that eventually infect the potato plants are carried by air currents projects first two years, the Ontario Potato Board obtained partial funding from theclose to the crop and deposited on the leaves or stems, she explains. So she tried Growing Forward program. In 2018, Syngenta, Bayer CropScience, Holmes Agro andplacing the traps at 90 centimetres above ground, which worked well.Alliance Agri-Turf provided the funding needed for the project. The project also showed the importance of scouting at least twice a week in Various kinds of spore traps are available on the market. For her project, Banksisolated fields with limited air movement, to complement the spore trap data. [In chose a Sporometrics Spornado trap for several reasons.one instance], the detection of spores was four days after a scout had found late They are passive spore traps; they do not require an external source of energy,blight in a field surrounded by trees. The trees delayed the spread of spores by the she explains. They are activated by wind. They require little maintenance. They usewind, resulting in a four-day delay in spore detection. The lesson learned was that filters rather than sticky slides to trap spores, and the filters are changed easily. potato growers should have intensive scouting on fields with poor air movement. The spores caught in the filters are identified in the laboratory by PCR, a veryThe passive spore traps have proved to be accurate predictors of the presence accurate molecular technology test. This was unique, and it was the main reason Iof late blight spores in a potato production area, Banks summarizes. This allows decided to evaluate these traps. With traps that use sticky slides, the spores needgrowers to time the application of late blight-specific fungicides. These fungicides to be identified using a microscope, which may result in misidentification.are more expensive and more susceptible to development of resistance than Banks used two traps per field and placed the traps in windy areas of the field.broad-spectrum products, she says. The filters were changed twice a week and were sent immediately to the lab. TheGrowers were pleased with the spore trapping technology and the quick lab provided the results by email to Ontario potato and tomato grower organiza- communication of results via email.46 SPUDSMART.COM FALL 2019'