PROJECT RESULTS

Management of White Mould in Beans Using Disease Forecasting Models and Fungicides

Applicant: 

Linda MacNair
Manitoba Pulse Growers Association
Carman, Manitoba  R0G 0J0  Canada

Table of Contents:

• Background and Objectives
• Procedure and Project Activities
• Results and Discussion
• Conclusions

ARDI Project:

#00-355

Project Status:

Completed January, 2001

Background and Objectives:

There were 180,000 acres of field beans produced in Manitoba in 1999, which is more than double the acreage in 1998. Based on monitoring by Manitoba Agriculture and Food, losses from white mould in the past five years have been close to ten percent. The cost of this yield loss is over four million dollars that could be returned from the use of an accurate application of fungicide. As field bean acreage continues to expand, disease incidence will increase due to shortened crop rotations. Integrated pest management of white mould is a key issue that needs to be investigated.

This study is part of an ongoing initiative that began in 1995. Fungicide trials conducted in 1998 indicated a difference in disease severity between irrigated and dryland trials. Environmental factors such as soil moisture, relative humidity, precipitation and temperature strongly influence the occurrence and spread of diseases. This project will determine the optimum efficacy and timing of fungicide applications in consideration of environmental factors. Comparisons will again be made between irrigated and dryland replicated plots, with the goal of establishing a white mould disease risk program for both types of management used in field bean production. This is a continuation of ARDI project number 99.254, which provided useful data in 1999 for the development of a white mould predictive model for beans. The risk prediction model will be compared to a model developed for sclerotinia of canola and modification will be made that will enable the bean model to be incorporated into Adcon software.

Procedure and Project Activities:

In 2000, three field sites were established with two at the Manitoba Crop Diversification Centre located at Carberry, Manitoba and one at Portage la Prairie. One field at Carberry and one field at Portage la Prairie were irrigated and the remaining field at Carberry received natural precipitation only. The fungicides used in this study were Benlate, Ronilan and Senator.

Weather conditions prior to fungicide application were ideal for development of white mould. Apothecia were observed in the area of all field sites. The application of fungicides to the plots at Carberry was done on July 20 with split applications applied on July 20 and July 30, 2000. The Portage plots were sprayed with fungicides on July 21 with split applications applied on July 21 and 31, 2000. Disease evaluation was based on the observation of 100 plants per plot. Disease severity was rated using an assessment scale of 0-4 where the percent surface area covered by lesions was equivalent to none (0), 1-25% (1), 26-50% (2), 51-75% (3) and 76-100%. The Carberry and Portage trials were rated for incidence of white mould on August 25 and August 22, respectively.

Soil Moisture was measured by means of a watermark type soil moisture probe. The probe measures soil moisture in kPa of pressure on a scale of 0 to 512 kPa. A value of 0 is taken as soil moisture saturation and a value of 512 is below the permanent wilting point. There were two moisture probes at each site (Soil Moisture White and Soil Moisture Yellow).

Results and Discussion:

Disease development was the result of infection by ascospores produced from sclerotia buried within the plots and may have involved natural inoculum as apothecia were observed in the area of all sites. Within sites, apothecia were first observed at the Carberry irrigated site on August 4. No apothecia were observed at this time within the dryland site. The incidence of white mould at the irrigated site (Carberry) ranged from 65.6 % (no fungicide application) to 22.8 % (Benlate - single application). At the Carberry dryland site, white mould incidence was less and ranged between 31.6 % (no fungicide application) and 12.7 % (Ronilan - single application). Similarly, at the Portage site, disease incidence ranged from 13.9 % (no fungicide application) to 0.2% (Ronilan - single application). Although disease levels at the dryland site in Carberry were higher than the irrigated site at Portage, it is likely that additional rainfall received at the Carberry site allowed soil to periodically remain moist enough to favour the germination of sclerotia and production of ascospores. At all three sites, application of Benlate, Ronilan or Senator as single or split applications resulted in less disease than in the plots where no fungicides were applied. In the 1999 trial, the lowest disease incidences were observed with the split applications of Benlate. In 2000 at the Portage site, disease incidence with the Benlate split application was low (0.7%), but did not differ significantly from any other single or split applications. Benlate applied as a single application produced a low level of disease at the irrigated Carberry site (22.8%) compared to the plots with no fungicide application(s). However, the Benlate single application did not differ significantly from the split application at this site.

Disease levels at the dryland site were lower than those at the irrigated sites. Weather conditions prior to flowering were conducive to the development of the disease, but periods of dry weather lowered the risk of white mould at the dryland site.

Environmental conditions at the dryland site (Figure 2) were not as conducive to disease development as at the irrigated site at Carberry (Figure 1). Moist soil conditions as a result of irrigation and a higher relative humidity provided conditions ideal for the development of white mould. Sclerotia require a period of ten days to two weeks of moist soil conditions before they germinate to produce apothecia. A more even distribution of moisture to provide longer periods of moist soil at the irrigated site was conducive to germination of higher numbers of sclerotia to produce apothecia and ultimately release ascospores.

Differences in levels of white mould between fungicide treatments are evident (Table 1) and these are reflected in the yield data (Table 2). At Carberry, the lowest yields were predominate in plots that were not treated with fungicides and this corresponded to greater disease incidences than in plots where fungicides were applied. Of the two Carberry sites, lowest yields were evident at the dryland site. Yields at the irrigated site ranged from 2627 kg/ha (no fungicide application) to 3556 kg/ha (Benlate - single application). At the Carberry dryland site, yields ranged between 2403 kg/ha (no fungicide application) and 3039 kg/ha (Senator - single application). Similar results occurred in the Carberry irrigated and dryland plots in 1999. Yields at the irrigated Portage site were less than those at the both the irrigated and dryland Carberry sites.

Development on Sclerotinia Risk Program

The 2000 research results indicated that the most important variable in the development of a sclerotinia forecast model is soil moisture prior to and during the flowering period. This was also the conclusion of (Bom and Boland 2000) in the Canadian Journal of Plant Science.

Apothecia development occurred in the irrigated Carberry site (Figure 1) on about August 4, following a period of 14 days of high soil moisture. Apothecia were not observed in the non irrigated Carberry site where the soil moisture was very low from July 22 to August 10. Extended periods of high soil moisture were found to be favourable for the development of Sclerotinia white mould as evident by the much higher infection levels in the irrigated versus the nonirrigated site at Carberry. Precipitation, relative humidity and temperature measurements were also recorded, but were not directly utilized in the forecast model development. Further field evaluation is required to validate the forecast model in commercial fields. The model needs to be programmed into Adcon software as the next step in this model development.

Table 1.  Effect of Benlate, Ronilan and Senator (single and split applications) on incidence of white mould of bean under irrigated (Carberry and Portage la Prairie) and dryland conditions (Carberry) in 2000. 

¹ Sclerotia were buried in all plots with the exception of the untreated A plots; data represents the mean disease incidence from 100 plants per plot (Carberry and Portage sites).

² Represent plots where no fungicides were applied.

³ Means within columns followed by the same letter are not significantly different at the 0.05 level

(Fisher’s least significant difference test).

Table 2.  Effect of Benlate, Ronilan and Senator (single and split applications) on the yield of bean under irrigated (Carberry and Portage la Prairie, 2000) and dryland conditions (Carberry).

¹ Sclerotia were buried in all plots with the exception of the untreated A plots; data represents the mean yield.

² Represent plots where no fungicides were applied.

³ Means within columns followed by the same letter are not significantly different at the 0.05 level

(Fisher’s least significant difference test).

Acknowledgments:

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