Alternaria leaf blotch and fruit spot

Alternaria leaf blotch and fruit spot is a fungal disease that causes dark, irregular lesions on apple leaves and fruit, reducing both tree health and crop quality. It can be particularly damaging in warm growing regions with high summer rainfall.

Disease identification

Alternaria leaf blotch is characterised by irregular red–brown lesions on the leaves that often exhibit blackish-purple borders. Typically, leaf blotch first appears from late spring to early summer and can increase in severity through to harvest.

Alternaria fruit spot is characterised by small, slightly sunken, light to medium brown spots appearing on the lenticels of the fruit, often surrounded by a black border. Fruit spotting is commonly observed in late summer through to harvest.

Damage

In favourable weather conditions, the alternaria leaf blotches will continue to grow, and when the leaf is half covered by lesions, it will turn yellow and drop prematurely from the tree. Fruit spotting symptoms appear after warm weather and usually no earlier than 42 days before harvest.

Monitoring

Due to the similarity of alternaria leaf blotch and fruit spot symptoms to those caused by other problems (e.g. fungal diseases and physical damage). If you are thinking of applying fungicides (or other treatments) to combat this disease, make sure the diagnosis is correct and consider having the symptoms assessed.

The presence of leaf blotch in mid-summer can be an early warning for the likely appearance of fruit spotting later in the season and the need for preventative sprays. Scout the orchard from late spring to look for symptoms of leaf blotch and again for fruit spot in late summer.

Be particularly vigilant with susceptible apple varieties including Fuji, Gala, Cripps Pink and Red Delicious.

Management

Cultural and physical: managing alternaria leaf blotch and fruit spot includes removing or breaking down all leaf and pruning residue during winter (after leaf fall), especially if there was leaf disease last season. In very small orchards, this is done manually by raking and removing leaf litter. In larger orchards, mechanised sweeping and mulching are more cost-effective at hastening the breakdown of last season’s leaf matter.

Biological: there are no known biological controls for alternaria leaf blotch and fruit spot in apples.

Chemical: refer to the Orchard plant protection guide for chemical suggestions.