DISEASES OF DRY BEAN IN MANITOBA IN 2019

A total of 40 bean crops were surveyed for both root and foliar diseases. Fusarium root rot was the most prevalent root disease and common bacterial blight the most widespread foliar disease throughout the province. Halo blight and sclerotinia stem and pod rot were also observed. In 2019, rhizoctonia root rot, rust and anthracnose were not detected in any of the 40 surveyed bean crops. METHODS: Crops of dry bean in Manitoba were surveyed for root and foliar diseases at 40 different locations. The survey for root diseases was conducted in mid- to late July when most plants were at the mid- to late flowering stage. The majority of the crops surveyed were selected at random from regions in southern Manitoba where most of the dry bean crops are grown, with 10% of the crops located outside of the traditional bean growing regions. During the root disease survey, the severity of halo blight (Pseudomonas syringae pv. phaseolicola) also was assessed. When the plants were starting to mature during mid-August, the foliar disease survey was carried out on the same fields assessed for root rot. For the root diseases, at least 10 plants were sampled at each of three random sites in each crop surveyed. Root diseases were rated on a scale of 0 (no disease) to 9 (death of plant). Fifteen symptomatic roots were collected from each of the 40 crops for fungal isolation and identification. Identification of Fusarium species involved visual assessment, microscopic examination and morphological characterization using the criteria of Leslie and Summerell (2006). Fifteen roots from each of the 40 crops surveyed were frozen for future PCR analysis of root rot pathogens. Foliar diseases were identified by their symptoms. Common bacterial blight (CBB) (Xanthomonas axonopodis pv. phaseoli) was assessed based on the percent incidence of leaf infection and on a severity scale of 0 (no disease) to 5 (50-100% of the leaf area covered by lesions). Anthracnose (Colletotrichum lindemuthianum), rust (Uromyces appendiculatus), white mould (Sclerotinia sclerotiorum) and halo blight (Pseudomonas syringae pv. phaseolicola) severity were assessed as percentages of infected plant tissue. RESULTS AND COMMENTS: Cool, damp conditions early in May hampered field operations in many areas of the province with drier conditions prevailing in the eastern half of the province. Wide temperature swings between daytime highs and overnight lows were reported in mid-to late- May with frost occurring on May 27th throughout most of the province (Manitoba Agriculture 2019a). By May 28th, seeding of the dry bean crop was 40-60% completed. Highly variable weather followed, with dry conditions and temperatures reaching 38 degrees C in the central region of the province. Strong south winds gusting up to 80 km/h caused soil blasting with damage to seedling plants in some fields. A drier than normal summer was followed by rainfall events that delayed dry bean harvest. Six percent of harvest was completed by September 10th compared to the 3-year (2016-2018) average of 25% completed by the same date (Manitoba Agriculture 2019b). Harvest continued to be slow due to widespread rainfall with 69% of the crop harvested by October 29th compared with 100% during 2016-2018 (Manitoba Agriculture 2019c). Seed quality suffered due to poor weather conditions and some crops were considered not worth harvesting. Average yields ranged from 1000 to 1500 lb/ac (Manitoba Agriculture 2019d) compared with the 2018 yields of 1400 to 2000 lb/ac (Manitoba Agriculture 2018). One root disease was identified (Table 1). Fusarium root rot was observed in all of the 40 dry bean crops surveyed, with severity ratings ranging from 2.3 to 5.8, and a mean of 3.8. It has been the most prevalent root disease of dry bean for several years (Conner et al. 2011; Henriquez et al. 2013; Kim et al. 2019a, 2019b). A number of Fusarium spp. including F. redolens, F. oxysporum, F. acuminatum and F. avenaceum were isolated from symptomatic root tissue. Rhizoctonia root rot (Rhizoctonia solani) and pythium root rot (Pythium spp.) were not detected in any of the crops surveyed based on microscopic examination and morphological characterization. Fourteen crops (35%) had average root rot severity ratings above 4 (i.e., symptoms were present on 50% of the root system and plants were stunted) and this would have had a detrimental effect on yield. There were more surveyed crops with average root rot ratings above 4 in 2018 (68%) and 2017 (63%). However, in 2016, a much wetter year, 93% of bean crops had severity ratings above 4, which represents the highest percentage of bean crops surveyed with yield-robbing root rot severity ratings over the past six years. In 2019, halo blight was assessed in the 40 crops surveyed and was observed in five (12%) crops with an average of 5% leaf area infected. Two foliar diseases were observed during the survey in August (Table 2). Common bacterial blight symptoms were observed in all 40 crops. The incidence of CBB leaf infection ranged from 5.0 to 36.7% with a mean of 16.1%, while severity ranged from 0.3 to 3.3, with a mean of 1.8. Anthracnose was not detected from 2014 to 2019, unlike many years prior to this period. Rust was not observed in any of the crops surveyed in 2019. White mould symptoms were detected in one crop with 1% of tissue infection. Seasonal precipitation in many of the bean growing regions of Manitoba was above normal in 2016, but below normal in 2017, 2018 and 2019 which would have contributed to the reduced risk of yield losses due to white mould in the latter three years. For example, in the Morden area, 371 mm, 162 mm, 213 mm and 224 mm of precipitation were received during May to August in 2016, 2017, 2018 and 2019, respectively, compared with the 30-year average of 305 mm for this four-month period (Government of Canada 2019). [GRAPHICS]