Carrot foliage trimmer for control of Sclerotinia rot in carrot

Project Code PRR06-310

Project Lead

Kevin Sanderson - Agriculture and Agri-Food Canada

Objective

To determine the effect of carrot foliage trimming on reducing apothecia and disease development in field grown and stored carrots

Summary of Results

Background

Sclerotinia rot of carrots (SRC) is a serious disease caused by the fungal pathogen Sclerotinia sclerotiorium and responsible for extensive crop losses across carrot growing regions of Canada. The disease is a major concern especially in the Atlantic regions where long periods of high humidity and wetness are common and where the majority of carrots are stored for long periods of time for winter sales. In Prince Edward Island (PEI) alone, the carrot industry can experience losses of up to $500,000 in any given season due to the disease, which translates to losses up to $1,600/hectare to the grower. However, at the time of the initiation of this project, there were no fungicides registered for the control of SRC and the growers needed effective alternative solutions to protect their carrot crops.

As a soil-borne disease, Sclerotinia rot starts with infection of carrot foliage, stem and root crowns in the field, but becomes more widespread in storage, where the main damage occurs. The release of spores from the pathogen is generally associated with carrot crop development, particularly canopy closure. At this time, the micro-climate within the canopy is moist and lacks sunlight and air movement, which provide perfect conditions for pathogen and disease development. Results from previous experimental studies conducted on carrots grown on muck soil in Ontario (ON) have demonstrated the positive effect of foliar trimming on SRC suppression. Foliage trimming is practiced commercially in some carrot growing areas of the US as a cultural method to control SRC. However, due to different production systems, the trimming equipment used in the US could not be adopted on most carrot growing areas of Canada. This project aimed at constructing a carrot foliage trimmer (CFT) prototype adapted to carrot production systems in PEI and demonstrating to growers the economic and environmental benefits of the trimming technology for SRC control.

Approach

A 3-year project, established and led by Agriculture and Agri-Food Canada (AAFC) scientists, was conducted at the AAFC Harrington Research Farm in PEI. The project focused on the design, construction and preliminary field testing of a CFT prototype. The CFT was designed as a tractor-mounted unit containing eight circular rotating saw blades capable of simultaneously trimming the canopy between four carrot rows. The CFT was designed to allow for the adjustment of trimming width between rows as needed. The CFT was evaluated and demonstrated in commercial fields of Brookfield Gardens Ltd., a local carrot grower in PEI. A combination of various trimming timings (2 weeks before, at, and 2 weeks after row closure) and canopy widths remaining over the row (44 cm or 52 cm) were compared to the untrimmed canopy. Trimming was conducted as a lateral clipping along each side of the carrot row using the tractor-mounted CFT prototype sometime between late-July and mid-August. Trimming resulted in cutting off the overlapping canopy and lodged senescing leaves. Yield and disease levels were compared between the trimmed and untrimmed plots in the field and harvested roots were evaluated in storage over the winter months.

Growers were informed about the project results and the new disease management approach through various means including factsheets, technical bulletins and posters, radio and TV announcements as well as presentations at meetings. In addition, a number of field days were held during the growing seasons to allow local growers to tour the demonstration fields and see for themselves the CFT in action and observe and discuss the benefits of trimming technology.

In 2009, the project focused on transferring the trimming technology to carrot production areas of Nova Scotia (NS) and expanding the scope to also include other major foliar diseases of carrot. This study investigated the effects of trimming on suppressing Alternaria leaf blight, Cercospora leaf blight and bacterial soft rot in addition to SRC on various cultivars of baby and sliced processing carrots. A secondary trimming of the carrot canopy prior to harvest was also evaluated. The study was conducted at the carrot farms of Oxford Frozen Foods Inc. in NS, the largest carrot production and processing company in the Atlantic region. The trimming in this study was conducted using a commercial tractor-mounted 9-row disc trimmer unit custom-built by Oxford Frozen Foods Ltd. Although not exactly the same as the AAFC prototype model, the Oxford trimmer resulted in efficient trimming. Disease levels and marketable yields were compared between the trimmed and non trimmed plots in the field and storage.

Results

Overall, the project demonstrated that side trimming the carrot foliage is an effective method to control SRC. In both 2006 and 2007 trials, the use of the prototype CFT reduced SRC disease up to 86% in the field and up to 77% in storage without affecting carrot yield. Foliage trimming at row closure appears to be the optimum timing to maximize SRC suppression, as compared to trimming two weeks before or two weeks after row closure. Growers observed additional benefits of canopy trimming, such as a reduction in foliar blights and bacterial soft rot with reduced need for sprays for these diseases as well as improved harvesting operation. A cost-benefit analysis conducted by the Oxford Frozen Foods Inc. revealed that the company could recover the cost of manufacturing the trimmer in 1-2 seasons as a result of reduced pesticide use, ease of harvest and improved quality of marketable crop.

Carrots on the demonstration farm and across PEI are typically grown on raised hills, similar to potato hills. But the technology appears to be versatile and easily adaptable to various cultivation systems, including raised or flat beds, and adjustable to varying row widths. Trimming is also a suitable approach for both conventional and organic carrot production.

The project team engaged in extensive knowledge and technology transfer activities, which led to significant media attention and grower adoption. As a result, two commercial trimmer units were constructed by industry collaborators and put to use in the 2007 growing season: a 9-row unit by the Oxford Frozen Foods Inc. in NS and one by Patrykus Farms in Wisconsin, USA. By 2008 and 2009, more commercial trimmer units were constructed in other parts of Canada (PEI, NS, ON) and internationally (United Kingdom, Scotland, France), all based on the original CFT technology developed as part of this project. For the growers using it, carrot foliage trimming has become an integral part of a standard integrated pest management strategy for sustainable carrot production.

This project provides an excellent example of fruitful collaboration among AAFC scientists, University researchers and industry to deliver a practical and affordable non-pesticide solution to a serious disease affecting carrot production.

For more details, please contact Kevin Sanderson or Rick Peters.

Fact sheet on the Carrot foliage trimmer for control of Sclerotinia rot in carrot

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