clubroot galls

Basamid fumigant is a potential tool for clubroot control

Basamid (dazomet) soil-applied fumigant was effective against clubroot and seedling blight in canola. Basamid appears to have good potential as a tool to maintain canola yield and reduce the spread of clubroot where the disease is concentrated, usually at field entrances.

Clubroot, caused by the obligate pathogen Plasmodiophora brassicae Woronin, is a well-established disease in Alberta, and found increasingly in Saskatchewan and Manitoba. The large galls that form on canola roots contain billions of long-lasting resting spores.  While longer crop rotations help to reduce the spore load, canola growers need additional tools other than clubroot-resistant hybrids to help manage the disease.

Greenhouse and field research led by Sheau-Fang Hwang with Alberta Agriculture and Forestry was conducted to examine the effectiveness of the prill formulation of the soil fumigant Basamid on root infection by P. brassicae, clubroot severity, and the growth and yield of canola. The research looked at variables such as application rate and the effect of plastic covering and ventilation period on effectiveness.

In greenhouse studies, canola was grown in soil containing high levels of P. brassicae resting spores. Increasing application rates of Basamid improved seedling emergence and plant growth, reduced primary and secondary infection by P. brassicae, reduced clubroot severity, and increased seed yield.

Effect of the application rate of dazomet (shown as the Basamid formulation) on (A) canola seedling establishment and plant height, (B) plant vigor, (C) weight of gall and clubroot severity (DSI), and (D) seed yield in clubroot-susceptible canola grown in an infested field near Edmonton, AB, in 2014 and 2015, n = 8 (2 trials × 4 replications).

dazomet clubroot effects
Source:  Hwang et al. 2017.

In field trials, increasing rates of Basamid reduced clubroot severity but also reduced seedling establishment, seedling vigor, and subsequent seed yield. Further greenhouse studies looked at the length of ventilation period between application and seeding.  It found that if canola was seeded 14 days after application, seedling establishment was reduced.  However, there was no effect if the canola was seeded 21 to 28 days after seeding.

Subsequent field trials confirmed that if canola was seeded 21 to 28 days after Basamid application, seedling establishment was improved, although not as high as the untreated control. Based on the results, the researchers concluded that an interval of at least one month between application and seeding is required. This interval would likely require delayed seeding into late May or early June, or treatment application in the previous autumn.

Further field studies showed that covering the soil with construction-grade plastic after Basamid application reduced gall weight and clubroot severity, and increased yield.

In soils that were also inoculated with the soil-borne seedling blight pathogens Fusarium avenaceum, Pythium ultimum, and Rhizoctonia solani, Basamid application also reduced the severity of these diseases and improved seedling emergence.  This suggests that Basamid is effective against both clubroot and seedling blight in canola.

Specialized training is required for safe application, and the use of a certified professional applicator is highly recommended.  Professional applicators also have access to specialized plastic films that increase the effectiveness of fumigants. Since Basamid is relatively expensive, the expected use of the fumigant would be to reduce spore load in areas where the disease is concentrated such as field entrances.  Basamid is currently not registered as a fumigant in canola.

 


S.F. Hwang, H.U. Ahmed, S.E. Strelkov, Q. Zhou, B.D. Gossen, M.R. McDonald, G. Peng, G.D. Turnbull. Suppression of clubroot by dazomet fumigant. Can. J. Plant Sci. 98: 172–182 (2018)

https://doi.org/10.1139/cjps-2017-0099

Photo by Sheau-Fang Hwang

The Canola Agronomic Research Program, the Alberta Crop Industry Development Fund, and Agriculture and Agri-Food Canada and the Canola Council of Canada through the Growing Forward 2 Program provided financial support.