Implementing a biological control agent as a pest management tool against leaf blight of onion

Project Code: BPI06-020

Project Lead

Odile Carisse - Agriculture and Agri-Food Canada.

Objective

To develop and implement a protocol for the application of the biocontrol agent Microsphaeropsis ochracea to control onion leaf blight caused by Botrytis squamosa.

Summary of Results

Every year 180,630 tonnes of onions are produced in Canada. Quebec and Ontario alone produce 70% of this on 4,087 hectares of land. In Quebec, onions are grown in an organic soil basin located to the southwest of Montreal. Every year, this rich, profitable and fragile ecosystem is faced with a significant problem: the intensive use of pesticides, including those used to control onion leaf blight. This airborne disease is so severe that 7 to 14 fungicide applications are needed every year. This heavy use of chemical pesticides poses a risk to non-target organisms and the environment, and so approaches to mitigate the risk are desirable. Unfortunately alternatives for managing the disease and reducing the risks from chemical fungicides are not always available.

Over the past years, Dr. Carisse's research team developed a microbial pest control agent (MPCA), Microsphaeropsis ochracea. Laboratory studies and studies in the field have shown that this MPCA is very effective in reducing the primary inoculum of the pathogenic fungi. It parasitizes the survival structures of certain types of melanised fungi, including Botrytis squamosa, the pathogen that causes onion leaf blight.

The goal of this project is to develop and implement a protocol for the application of M. ochracea as a pest management tool against leaf blight of onion. The approach consists of using M. ochracea to reduce the pathogen's primary inoculum, leading to a delayed, and therefore reduced, number of chemical fungicide applications. M. ochracea will be used in combination with a fungicide regime based on the actual disease risks determined using measurements of the airborne inoculum and leaf lesion scouting.

Tests on experimental plots revealed two important facts concerning the use of M. ochracea. First, the efficacy of the microorganism varies from year to year. In fact, an 83% reduction was observed one year in the number of spots per leaf, and a 45% reduction the next year. Second, tests on small plots are difficult to interpret because of the interference between plots. Since B. squamosa spores are spread in the air, they travel from one plot to another. In the end all the plots become contaminated, and so the effects of the autumn treatments are hard to detect.

Two onion producers that are members of the scouting network PRISME in the organic soil region to the southwest of Montreal conducted tests on commercial plots. In late September the plots were treated with the commercial formulation of M. ochracea at the rate of 1x1011 spores per hectare. During the summer of 2007, the concentration of airborne spores and the number of spots per leaf were recorded for the entire growing season.

The first producer found that, at the start of the season, there was a reduced incidence of the airborne inoculum in the plot treated with the biological control agent. From June 1 to 18, the treatment threshold was reached or exceeded three times in the untreated plot while it was not reached on the plot treated on July 17, that is, more than one month later. The use of M. ochracea by this producer delayed the leaf blight epidemic, reducing the application of fungicide by 50%. However, the second producer had much more severe leaf blight, and the application of M. ochracea did not allow the use of fungicides to be reduced.

The study results lead us to believe that the biological control agent M. ochracea partly destroyed the B. squamosa sclerotia, thereby reducing inoculum numbers at the start of the season. However, once the epidemic has started, there is no noticeable difference in the progression of the disease in treated and non-treated fields.

There would be much more interest among producers if M. ochracea could be combined with the biofungicide Contans® (Conithirium minitans), which controls white mold in carrots. According to a survey of producers, 26% would be interested in using a product only composed of M. ochracea, while 53% would be interested in using a product that would also control white mold in carrots. This is probably due to the fact that many onion producers also produce carrots, or else include them in their crop rotations. More information must be collected to convince producers of the short- and long-term benefits of including biological control products in their cropping.

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