Impact of Sclerotinia Stem Rot on Yield of Canola.

Sclerotinia sclerotiorum is the causal agent of Sclerotinia stem rot (SSR) of canola (Brassica napus). In North Dakota, the leading canola producer in the United States, SSR is an endemic disease. In order to estimate the impact of this disease on canola yield, field experiments were conducted from 2000 to 2004 at several locations in North Dakota and Minnesota. Experimental plots were either inoculated with laboratory-produced ascospores or infected by naturally occurring inoculum in commercial fields. Applying fungicides at different concentrations and timings during the flowering period created epiphytotics of diverse intensities. Disease incidence was measured once prior to harvesting the crop on 50 to 100 plants per plot. Results of the study indicated that 0.5% of the potential yield (equivalent to 12.75 kg/ha) was lost for every unit percentage of SSR incidence (range of 0.18 to 0.96%). Considering the current cost of fungicide applications and the market value of this commodity, a 17% SSR incidence could cause losses similar to the cost of a fungicide application. Additional efforts are required to improve current levels of tolerance of canola plants to this pathogen.

Efficacy of Fungicides for Control of Sclerotinia Stem Rot of Canola.

Sclerotinia stem rot (SSR), incited by Sclerotinia sclerotiorum, causes yield reductions to canola (Brassica napus) grown in North Dakota and Minnesota. Field trials were conducted in North Dakota and Minnesota from 2000 to 2004 to evaluate the effect of foliar fungicides on SSR and canola yield. Levels of SSR varied among years and location. In general, fungicides that consistently reduced SSR incidence compared with an untreated control were azoxystrobin, benomyl, boscalid, iprodione, prothioconazole, tebuconazole, thiophanate-methyl, trifloxystrobin, and vinclozolin. Significant reductions in SSR incidence with fungicides did not always translate into differences in canola yield, however. Inconsistent results were observed with different timings of applications based on percent bloom. This indicates that application timing should be based on factors in addition to percent bloom.

Impact of White Mold Incidence on Dry Bean Yield Under Nonirrigated Conditions.

Studies on chemical control of white mold, conducted between 1994 and 2001 at several locations in North Dakota, resulted in diverse levels of white mold incidence and severity. Navy bean cultivars were evaluated in on-farm trials between 1994 and 1996, while pinto bean cultivars were used between 1997 and 2001. The relationship between yield and white mold incidence in these trials was examined using correlation and regression analysis. White mold incidence was correlated to severity using a second-degree polynomial equation (R 2 = 0.90, P = 0.0001) in pinto bean experiments. For every percent unit increase in white mold incidence, yield was reduced by 12 kg/ha (range 7 to 19 kg/ha) in pinto bean and by 23 kg/ha (range 19 to 26 kg/ha) in navy bean. In both instances, the coefficients of determination were significant (P < 0.04) for most locations or years, and ranged from 0.42 to 0.87 for pinto bean and from 0.98 to 0.99 for navy bean. Fungicide-protected plots had an average white mold incidence of 34 and 50% compared with 76 and 73% in nonprotected plots for pinto and navy bean, respectively. Fungicide applications increased yields by 33 and 26% (P ≤ 0.05) for pinto and navy bean, respectively.