In winter, look for distinct cankers or dead blossoms particularly on susceptible varieties.
Inspect orchards for wilting /dying blossoms from the end of blossom.
The presence of infected blossoms in one season indicates the need for fungicide treatment the following season.
Forecasting models have been developed in other countries for other Monilinia species (M. fructicola and M. laxa) on stone fruit, but not for apple blossom wilt.
The development of specific forecasting systems is probably not merited as control can be achieved by a few well-timed protectant sprays.