Tan spot (Pyrenophora triticirepentis)is an important disease of wheat in many parts of the world.
• In the 2012/13 season tan spot was observed in South Canterbury, the Fairlie Basin and the Hakataramea Valley. We have already received reports this season of the disease showing up outside of these regions, in Southland and Central Canterbury.
• Tan spot is a stubble borne disease, so wheat following wheat is at highest risk of early infection. However later in the season all wheat crops can be infected as a result of wind-blown secondary spores (conidia)
• Selection of cultivars with more resistance will help, but resistance is unlikely to be complete.
• Reducing inoculum by burying or burning stubble are the most effective prevention measures.
• Fungicides are unable to provide any real curative activity, however overseas data suggests that programmes focussing on the flag and ear sprays are the most effective at preventing disease build up on the top two leaves.
• A broad spectrum combination of triazole and strobilurin applied at robust rates on the flag leaf and again on the ear is a good option for second or continuous wheat crops.
• Growers outside the higher risk areas may not need to change fungicide strategy to take account of this disease unless it is observed in crops prior to flag leaf.