Alternaria leaf blotch and fruit spot

 

 

ALB is primarily spread from spores which remain on winter prunings, leaf litter, dormant leaves and flower buds. ALB is relatively inactive early in the season, however summer rain and humidity, rapidly causes ALB to spread. Once infected, lesions form on leaves which release spores when splashed by rain, causing secondary spread of ALB throughout the orchard. Trees already suffering from other diseases or pests are more prone to becoming infected.

Symptoms on leaves appear as brown to purplish irregular spots surrounded by a black border.  They can become necrotic and defoliation can occur. Fruit develops light brown sunken spots on the skin, which can be confused with other disorders, such as alternaria core rot (Alternaria alternata). In Queensland and New South Wales, fruit damage is common and economic losses are significant. Pre harvest spots stop growing when fruit is placed in cold storage, however upon removal spots become bigger and new ones can form, providing an entry point for other diseases. Trees affected by ALB can also suffer from premature defoliation which can lead to long-term reduction in tree vigour and yield.  

 

 

Preventative control measures are vital for controlling ALB. Foliar and ground applications of urea well after harvest can assist in the rapid breakdown of leaves helping to reduce levels of overwintering spores. Removal of winter prunings and fallen leaves also help minimise spread.

Providing adequate nutrition, water and maintaining overall tree health may help reduce the severity of infections and leaves should be regularly monitored for the presence of disease.

When required, fungicides such as Luna^® Sensation are best applied early in the season just after petal fall. Luna Sensation can be applied from green tip through to 14 days prior to harvest.

Luna Sensation is registered for the suppression of ALB in apples.