AgronomyA New Early Warning System for Late Blight

    A New Early Warning System for Late Blight


    [deck]Although still at the experimental stage, initial results look promising for the use of spore traps as a tool for disease forecasting and fungicide scheduling.[/deck]

    Late blight, caused by the fungus Phytophthora infestans, remains the most serious and destructive disease of potatoes. Growers have relied on chemical sprays for many years to prevent serious outbreaks of late blight in their fields, and chemical companies around the world constantly strive to develop new and more effective formulations of fungicides to control the disease. Chemical sprays come at a high price though, and in some areas the treatment of potato crops to prevent the onset of late blight comprises a significant percentage of overall crop input costs. Researchers in the Atlantic provinces have found that fungicides represent more than 80 per cent of the active ingredients used on potato crops during an average growing season.

    In the search for solutions to the issues associated with the scheduling of chemical sprays, researchers and specialists have developed several late blight prediction models and programs, mostly focusing on prevailing weather situations during the vulnerable periods of crop growth throughout the season, although some systems also incorporate spray history, growth stage and variety type. These decision support systems are designed to warn growers of the potential onset of a “late blight period” or “late blight weather,” and growers can take the preventative measure of spraying their crops.

    During the past number of years, the Quebec-based company Phytodata Inc. has developed a novel disease-detection technology for accurately predicting the onset of high-risk late blight periods during the growing season. Since the 1990s, Phytodata technicians have been looking for technologies that could help them detect disease-causing spores in the air before symptoms appeared in plants. In the late 1990s, Phytodata designed specialized equipment, called “spore traps,” which are placed in the fields of specific geographic locations to capture the spores of disease-causing organisms.

    “Spore production, dispersal and germination on a susceptible host, such as potatoes, play a critical role in late blight epidemics,” says Yves Leclerc, director of agronomy at McCain Foods Canada. “Spores can be dispersed by wind and rain from a few metres to hundreds of kilometres,” he notes.

    According to technical specialist Hervé van der Heyden at Phytodata, “We started to use spore traps to help us understand the relationship between weather parameters and disease incidence and severity. Our first model was Botrytis squamosa, a disease infecting onion crops. In 2008, we had our first trial with potato late blight in Quebec with four sites where six traps had been installed, and samples were taken six days a week. Our objective was to reduce the use of fungicide by minimizing unnecessary sprays.”

    The catching device of a spore trap consists of two plastic rods, which are 20 millimetres by two millimetres. These rods are coated with silicone grease where spores and other aerial particles are trapped over time. The rods are attached to a small rotor that spins at 2400 rotations per minute, with a sampling rate of 20.65 litres of air per minute, Van der Heyden explains. “The traps are operated three times per week between 6 a.m. and 3 p.m., and the rods are collected and removed from the traps every day, while a reading is taken every alternate day. At every spore trap a small weather station is also installed so that we can obtain accurate climatic information related to infection modeling,” says Van der Heyden.

    After the spores are collected from the rods, they are analyzed in the Phytodata laboratory using a new technology called “DNA detection,” which is also used in the detection of disease in humans. Technicians operate a specialized machine that can process up to 24 spore traps in two hours, after which a report is compiled detailing the spore count in each field.

    In 2009, while continuing with the Quebec trial, Phytodata started working with McCain Foods in New Brunswick, where six spore traps were installed at the McCain research farm. In 2010, 15 spore traps were installed between Woodstock and Grand Falls, and this network was reinstalled in 2011.

    Eight spore traps were also installed on Prince Edward Island between 2010 and 2011. “The objective was to monitor late blight spore dispersal and quantify spore load in real time to assist with disease forecasting and fungicide scheduling,” says Leclerc.

    Additionally, Phytodata started working on spore traps to capture early blight (Alternaria) spores in 2010 in cooperation with Philippe Parent, an agronomist at Patates Dolbec, a seed potato operation in Quebec.

    Leclerc is of the opinion that spore traps have, to date, accurately reflected real-time spore load during the trials. “Spore counts increased following infection periods, with the highest spore counts recorded following periods of highest infection risk,” he says. “Traps also proved useful for identification of local inoculum sources.”

    Leclerc is optimistic about the potential of the technology, but notes that this is a technology that works best when there is a network of spore traps within a particular geographic region. “We are still at an experimental level with the technology. More research is needed on exactly how to use this tool before making late blight spray recommendations, but the initial results look very promising. We are confident that this technology can work as an early warning system and as a means to complement existing decision support systems.”

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