Relevance of Mills infection periods to apple scab (Venturia inaequalis) prediction and rescheduling fungicide' applications in Himachal Pradesh

Abstract

A study was conducted during 1990-96 on the relevance of Mills scab infection criteria for improving efficiency
in the monitored apple scab control programme. The investigations on the length of leaf wetness for the majority of
infection periods (light, moderate and severe) occulted, indicated 1-3 days delay for symptoms development under
Himachal Pradesh conditions. The observations recorded on potted and orchard plants showed that the light infection
period required at least 3 days more for the development of scab symptoms at leaf wetness between 9.0-13.4 hr and at
average temperature range between 8.S-21AoC, whereas moderate and severe infection periods (>15.0 hr leaf wetness)
required 1 more day to exhibit the symptoms. The rescheduling of fungicide applications on the occurrence of infection
periods, however, saved aileast 3 sprays in comparison to 8 protective sprays in the growing season. Prediction and
monitored spray programme may be devised in accordance to the prevailing weather conditions of the region.