FUNGICIDE EFFECTS ON THE DEVELOPMENT OF PHOMA-LINGAM IN WINTER OILSEED RAPE

Investigations concerning the biology and epidemiology of Phoma lingam (teleomorph: Leptosphaeria maculans) the cause of crown and stem canker of winter oilseed rape revealed that windborne ascospores are the main inoculum for primary infections. High degrees of latent infections up to 90 % could be detected already in autumn. After spraying Sportak and Folicur (1,2 resp. 1,5 1/ha) at three different times in autumn and once in spring, the efficacy against leaf spot, incidence of latent infections at crown region resp. severity of crown canker, was quantified at five sites in 2 years under moderate resp. high disease pressure. Treatments in the autumn, provided the greatest reliability in reducing crown canker with different success resulting from treatments early, in the middle or late in the fall. Early applications in the three to four-leaf stage end of September (EC 19-21) were less effective than treatments in the middle and at the end of October (EC 23-26), which reduced the portion of severely damaged plants until harvest up to 50 %. Spring treatments could reduce the degree of crown canker only if primary infections occurred later in autumn. By eliminating other factors of damage (Psylliodes chrysocephalus, Ceuthorhynchus napi, Meligethes aeneus, Sclerotinia sclerotiorum, Alternaria spp.) and using a suitable trial design and harvesting technique (plot size 32-37 m2, harvesting 21 m2) yield losses between 8 up to 20 % could be proved by single treatments in autumn (EC 23-26) which was mainly the result of the control of crown canker. Combined treatments in autumn and spring (EC 23 + 33 resp. EC 24 + 51) reduced yield losses from 12 to 17 %. Single treatments in spring especially with Folicur increased yield up to 13 % which was not only the result of decreasing the crown canker of Phoma lingam. The timing of fungicide treatments to control crown canker is discussed in relation to the epidemiology of Phoma lingam as well as factors which are influencing disease development and yield reactions.