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Carrot trimmer implementation for white mold management in Ontario

Project Code: PRR09-010

Project Lead

Mary Ruth McDonald - University of Guelph


To conduct on-farm demonstrations and extension activities for promoting grower adoption of carrot foliage trimming to manage white mold of carrot in Ontario

Summary of Results


Carrots are the second most valuable fresh market field vegetable in Ontario. Sixty percent of carrot production in Ontario is concentrated in the Holland Marsh area, which produces about 25% of all the carrots grown in Canada. White mold, also known as Sclerotinia rot disease, is caused by the fungal pathogen Sclerotinia sclerotiorum. It is the most destructive disease of carrots in storage, sometime causing complete loss of carrots, but more often forcing a grower to sell early, thereby loosing revenue expected for his crop. The disease can sometimes also cause losses in the field, but most importantly, root infection causing crop losses in storage results from foliar infection in the field.

Once the carrot canopy closes and begins to lodge, conditions of higher humidity and poor air circulation beneath the canopy become conducive for pathogen development. At this time, the pathogen infects old, senescing carrot foliage that is in contact with moist soil. The infection then travels down the petioles into the crown. Keeping the carrot canopy open through trimming has been shown as an effective method of preventing disease by altering the microclimate and making it unfavourable for spore formation and leaf infection. Carrot foliage trimming is a commercial practice in Washington State and in the Maritime Provinces of Prince Edward Island (PEI) and Nova Scotia (NS). This project aimed to build and demonstrate to growers a trimmer equipment suitable for use under the commercial carrot production conditions in the Holland Marsh area of Ontario.


A 3-year project was established in Holland Marsh by the University of Guelph scientists in cooperation with local carrot growers and agricultural machinery manufacturers. The project team collaborated closely also with the Agriculture and Agri-Food Canada’s (AAFC) researchers previously involved with the development and demonstration of the carrot trimming technology in PEI and NS. The project started with a trip of the project team and grower cooperators from Ontario to meet with the AAFC’s research team and visit growers in PEI and NS using commercial trimmers to manage white mold in their carrots farms. The project team had a unique opportunity to view first-hand the various trimmer models in action and also discuss engineering details on trimmer fabrication to meet the needs of Ontario growers.

As part of this project, a new trimmer was constructed based on the models adapted in the Maritimes, but some modifications and adjustments were made to the trimmer design to allow it to work effectively in muck (organic) soils of the Holland Marsh. The new trimmer was then tested and demonstrated in a number of commercial carrot fields during the 2010 and 2011 growing seasons. Trimming was conducted as a sideways clipping along the carrot rows, soon after the canopy was closed, removing about 30% of the canopy width on each side of the carrot row and cutting off most of the overlapping and lodged senescing leaves. An open area of 32-34cm wide resulted above the furrow between the carrot rows. Yield and disease levels were compared between the trimmed and untrimmed plots in the field and harvested roots in storage over the winter months.

Two surveys were held at the start and at the end of the project to gauge grower knowledge, acceptance and preferences to better promote the adoption of the carrot trimming technology.


The demonstration trials in Ontario confirmed results from previous studies in other regions that mechanical foliar trimming is very effective at reducing white mold disease of carrot without affecting the marketable yield. In the field, disease reduction of up to 12% was achieved. No significant differences were found in the 2010-2011 storage assessments, perhaps because of fairly low disease pressure during the 2010 growing season. For best results, trimming is recommended to be conducted when the carrot canopy has just begun to close, which usually occurs around mid-late August in Ontario, depending on weather, planting date, carrot cultivar etc.

Field days were held at the demonstration sites during the summer to provide local growers with an opportunity to view the carrot trimmer in action as well as to inspect and inquire about it. Presentations on project results were made annually at local grower meetings. Surveying growers participating at these meetings revealed that a combination of research and extension work in the project has led to increasing grower interest in adopting the trimming technology as part of their management strategies.

Trimming is considered an environmentally friendly cultural control method suitable for both conventional and organic carrot production. It can replace pesticide applications to control white mold under low disease pressure, and can improve the efficacy of fungicide treatments when disease pressure is high. Trimming can thus, decrease fungicide use by up to 3 sprays per season, which is the maximum number of sprays in conventional crops. The trimmer was also used a second time, later in the growing season to assist with carrot harvest, where it was shown to effectively reduce binding and foliage build-up in the carrot combine. A cost benefit analysis indicated that using the carrot trimmer had significant economic benefits.

Currently, there are only two fungicides, Allegro (foliar application) and Scholar (post-harvest application) available for use to control white mold of carrot. Therefore, it is important to integrate cultural practices such as foliage trimming along with chemical products and other available tools (e.g. biofungicides) to achieve sustainable management of the disease.

For more information on thus project please contact Dr. Mary Ruth McDonald.

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