Loose smut - be on the lookout
Recent scouting in the southeast part of Saskatchewan is turning up loose smut in some cereal fields. This disease has different causal agents that are host specific. On wheat and triticale, it is caused by the fungal pathogen Ustilago tritici while on barley and oat, U. nuda and U. avenae are the causal agents.
Loose smut is a seed borne disease where the seed has been infected at flowering during a previous growing season but manifests itself in the year in which the seed is planted. Weather conditions that favour the disease are cool, moist weather during flowering with 95 per cent relative humidity and 20 to 25 Celsius.
Teliospores will become airborne or will be washed off by rain. An empty rachis will be the remaining sign of the disease. If weather conditions are conducive to development, they will land on florets and germinate.
Historically, loose smut was mentioned in the First Annual Report of the Survey of the Prevalence of Common Plant Diseases in the Dominion of Canada. The report was submitted in 1920 by the Canadian Phytopathological Society and claims one field in Saskatchewan showed a five per cent infection rate.
If we fast forward to now, loose smut, while still present in the environment as seen this season, can be kept in check by seed treatments. Other cultural techniques that mitigate this disease are using resistant varieties, seed testing to ensure the usage of disease-free seed and the strategic use of systemic fungicide seed treatments. Hot water seed treatment can be used in organic systems, but care must be taken to manage the water temperature or seed germination can be affected.