Can Foliar Fungicides Bump Edible Bean Yields & Quality?

Dry bean growers are familiar with the use of fungicides to protect against white mould and anthracnose. Both diseases can have devastating impacts on yield and quality of dry beans. During the past 3 seasons, white bean growers have experienced localized outbreaks of anthracnose that have reduced yield and increased dockage and pick. Growers and researchers are now looking to test if using a foliar fungicide can boost dry bean and soybean yields, even in the absence of disease. 

Part of the interest in foliar fungicides stems from the static yields of dry beans (and soybeans). With the exception of the past two seasons of record dry bean yields, the provincial yield has remained relatively static around 14 – 15 cwt/acre. While genetic improvements in dry beans continue to be made, growers have struggled with consistently realizing these improvements. The industry is now looking at how more intensive management can ‘tweak’ plants to yield more through improved ‘plant health’. 

Research

There has been some research that shows the use of a fungicide in the absence of disease results in visibly longer retention of green leaves and measurable improvements in yields. BASF and Syngenta Crop Protection report in some company and grower trials, improved plant health late in the season, and a boost in yields. The Strobilurin fungicides, such as Headline (BASF) and Quadris (Syngenta), are of particular interest because of the suggestion that not only do they work very effectively against targeted diseases, but they also influence the plants physiology. These effects can include reducing the production of ethylene in plants late in the season, and therefore delaying leaf drop and plant senescence, improving carbon assimilation, improving plant growth efficiency and increasing tolerance to stress during flowering and pod fill. 

However, the data that supports a payback to growers is not always clear-cut. One piece of soybean research that is capturing media attention is a report by Marty Draper, Plant Pathologist at South Dakota State University. Draper summarized foliar fungicide trials on soybeans across 65 locations in the north-central Midwest in 2005. Some of the trials had some level of secondary foliar disease, while others did not. In about one-third of the trials, application of a strobilurin fungicide yielded at least an additional 4 bu/ac, one-third showed 0 – 4 bu/ac more, while one-third showed a yield loss compared to an untreated check. In two-thirds of the trials, the grower would not have made any additional money after the cost of the treatment. 

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Edible Bean Trials

In edible beans, the research into the benefit of a late-season application of a strobiluron is just getting started. Chris Gillard, RCAT (U of Guelph) is researching the impact these products have on plant health and yield of white beans, cranberry, and kidney beans. The Ontario Coloured and White Bean producer groups are working with BASF and Syngenta on a research and field trial project to evaluate the plant health and yield response to Headline and Quadris. Growers are encouraged to conduct their own trials, and include at least 2 unsprayed (check) strips in a field. This will allow evaluation of both a visual level of plant health and yield measurement. It is important to time application of the fungicides correctly. For example, the suggested application timing for the trial of Quadris is at one open bloom, so it is important to stage the crop correctly. Growers should contact the product representative for information. Growers may obtain a plot outline by contacting Brian Hall, OMAFRA (519-271-0083 or Chris Gillard, RCAT will also be conducting small plot research in conjunction with the on-farm trials. 

IPM Strategy Still The Only Game In Town

For dry bean growers, the best management strategy for now is to remember that the primary function of fungicides is to control specific diseases. Controlling diseases is best accomplished by an integrated approach that includes crop rotation, sanitation, scouting, and using weather and disease forecast models. Broad-spectrum fungicide application without targeting specific diseases may promote earlier disease resistance to a fungicide. These products are very specific in the diseases they control and timing is critical. Last year, some growers applied a strobilurin for control of bacterial blight, for which these products do not work. A heavy late-season outbreak of Common Blight was widespread in some areas. This resulted in earlier plant maturity, and increased dockage and pick at the elevator, for which the grower could do nothing. The best management strategy for blight at present is to use blight-free seed. Genetics holds promise, with the release of OAC REX, the first white bean variety resistant to blight.

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