The effect of post-harvest epidemics of powdery mildew on yield and growth of strawberry cv Elsanta

Severe epidemics of powdery mildew develop post-harvest on June-bearing strawberry cultivars such as Elsanta. Previous studies have shown such attacks to have no effect on yield the following season. In the current study initiated in 1992, up to 14 sprays of myclobutanil or bupirimate were required to achieve control. However, this did not result in significant differences in total yield between treatments in any year. Plants mildewed the previous autumn were significantly smaller in winter but differences in size disappeared quickly with the resumption of rapid growth in spring. In each of the three seasons of the current study mildew failed to develop on untreated plots in spring, despite the high disease levels the previous autumn. Subsequent studies in the plots indicated that leaves infected with mildew in November at the end of the epidemic had senesced by the following spring. However, in a second crop, where large numbers of cleistothecia of Sphaerotheca macularis were present the previous autumn, mildew was first noted in April. This indicates a need to re-examine overwintering of the strawberry powdery mildew fungus in the UK.