Disease

Blossom blight and brown rot

Details: By NSW DPI

Blossom blight and brown rot are the most important diseases of stone fruit.

The causal fungi are the two related pathogens, Monilinia fructicola and Monilinia laxa.
Disease identification
Blossom blight results in brown, shrivelled, dead flowers (Figure 1) and some dieback of the associated shoot growth.
Brown rot infection appears as a soft brown decay of the developing fruit, which exhibits profuse brown–grey spores over the surface of the infection as it matures (Figure 2).
Infected fruit will sometimes shrivel and hang on the tree. These mummified (or mummy) fruit (Figure 3) and infected shoots are a major source of carryover spores for the next season.
Damage
Blossom blight and brown rot can cause significant flower, shoot and crop loss if not carefully managed.
Blossom blight reduces the number of viable flowers and causes damage to fruiting shoots. Brown rot makes fruit unsaleable and late-season infections can lead to fruit breakdown during postharvest storage, handling and marketing.
Monitoring
Blossom and/or fruit infection is likely when the disease was present in the previous season and warm conditions (around 20C or greater) combined with moisture from heavy dew or rainfall.
Due to the high potential for losses, particularly in warm wet seasons, it is worth monitoring for these diseases regularly. Check flowers, shoots and developing fruit for signs of rot at least weekly and particularly following favourable weather conditions.
Management
Cultural and physical
Remove and destroy infected shoots and mummified fruit as soon as they are noticed. Doing this early in the season will reduce the potential for it to spread to healthy fruit later in the season.
Winter pruning is a good time for a final check to ensure all mummified fruit and infected shoots are removed before the start of the new season.
Biological
There has been some research into the effects of antagonistic yeasts as a potential bio-control for Monilinia species in stone fruits. However, there are currently no commercially available bio-control treatments.
Chemical
An effective spray program for blossom blight and brown rot will include a combined approach of protective cover sprays and curative fungicides as needed from bud burst through flowering and to harvest, depending on weather conditions and disease pressure. Postharvest chemical options are also available.