Septoria tritici blotch
Mycosphaerella graminicola (sexual spores), Zymoseptoria tritici (asexual spores)
Septoria tritici blotch (STB), also known as septoria leaf spot or speckled leaf blotch, is a fungal foliar disease affecting wheat in Australia. Previously STB has been effectively managed through crop rotations and farming practices, however recent changes to farming systems including stubble retention, intensive wheat cropping and sowing of susceptible varieties has seen an increase in prevalence of STB, particularly in the cooler, high rainfall regions. Yield reductions of 20 per cent or more in susceptible varieties can occur as well as grain quality reductions. Hosts include wheat and triticale; however durum wheat and triticale tend to have higher resistance to STB.
Description
STB causes pale grey to dark brown, irregular and elongated lesions or blotches, usually on the lower leaves of young plants. In rare cases, or during wet springs when infection may occur later, lesions can extend into the stems and heads. STB may be confused with similar leaf diseases such as septoria nodorum and yellow spot. It is usually easily distinguished by the shape of the lesions and the presence of black fruiting bodies (pycnidia) within the blotches. In severe infections, entire leaves can be affected and late infections often accelerate maturity, causing shrivelled grain.
STB is stubble-borne and survives from one season to the next on infected stubble. During late autumn/early winter after heavy dew or rain, wind-borne spores (sexual) are released. These can travel long distances, landing on young wheat seedlings causing primary infection. Once infected, lesions on leaves develop along with fruiting bodies full of spores (asexual) and when splashed by rain, spores are readily dispersed onto new leaves or neighbouring plants causing secondary infection. Infection requires temperatures of 15 - 20 °C and rain, with leaf wetness of at least six hours to be successful. Severe outbreaks of STB are more common in seasons with above average rainfall.
Control
STB has developed resistance to some fungicides, therefore it is best to take an integrated management approach. STB survives on stubbles hence crop rotation is important; a one-year gap between wheat crops can be highly effective at reducing early infections. If a known STB outbreak has occurred, sowing may be delayed to avoid infection by spores released early in the season. Variety selection is crucial, where possible plant resistant varieties, especially in a wheat on wheat rotation. Reduce or manage stubbles by burying, burning or grazing to help reduce disease levels. Care must be taken in paddocks that are prone to wind or water erosion. It is important to monitor crops to determine if an application of fungicide is required and rotate chemicals with different modes of action to reduce the risk of resistance. Consult CropLife Fungicide Resistant Management Strategies as a guide to the responsible use of fungicides and always follow the product label for specific use instructions.
Some seed dressings such as Jockey® Stayer® will provide suppression of early infections of STB (Mycosphaerella graminicola) in wheat. Ensure even coverage with a seed dressing for best results.
Aviator®Xpro® is a combination of two fungicide groups, which offers both curative and protective control of STB (Zymoseptoria tritici) in wheat.
References
Department of Primary Industries and Regional Development (DPIRD) (2016), ‘Diagnosing septoria tritici of wheat’, https://www.agric.wa.gov.au/mycrop/diagnosing-septoria-tritici-wheat
Holloway, G (2014), ‘Septoria Tritici Blotch of Wheat’, Agriculture Victoria, http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/grains-pulses-and-cereals/septoria-tritici-
GRDC (2014), ‘Managing Septoria Tritici Blotch Disease in Wheat’, Septoria Tritici Blotch Fact Sheet Southern Region, https://grdc.com.au/__data/assets/pdf_file/0024/159342/final-septoria-tritici-blotch-fact-sheet-lr-pdf.pdf.pdf