Effects of sharp eyespot on yield of wheat (Triticum aestivum) in New Zealand

Abstract

The incidence, severity, and effects on yield of sharp eyespot (caused by Rhizoctonia cerealis van der Hoeven) in New Zealand wheat (Triticum aestivum) crops were assessed over 4 years (1996–2000). In 1998/99, 37 crops were examined, and symptoms of sharp eyespot were recorded in 43% of them. The disease was particularly common in south Canterbury. Laboratory isolations confirmed that R. cerealis was the causal organism. Sharp eyespot was detected in 17 of 19 crops selected for detailed examination between 1996 and 2000. Incidence in individual crops ranged from 2 to 88% of tillers infected, and differed between years. Mean yield losses as a result of sharp eyespot in infected crops were estimated at 6, 1, 8, and 14% respectively over the 4 years. Yield loss was related to disease incidence and was considered to be negligible when the incidence was <10%. The maximum individual yield loss was estimated at 18%. Losses were the result of reductions in both grain number/ ear and grain weight and were greatest in moderately to severely infected tillers. Although sharp eyespot is not a major yield‐limiting disease of wheat in New Zealand, it can reduce yields considerably under conditions conducive to its establishment.