IPDM Masterclass APAL Technical Symposium with Stephen Tancred

Following the IPDM masterclass at the APAL Technical Symposium with Stephen Tancred in Shepparton this year, the below are some pest and disease notes to keep in mind for late winter as we start to approach green tip.

Powdery Mildew

Powdery mildew damage occurs at flowering and fruitlet formation, damage is not immediately evident but appears as webbing on maturing apple. Infection of new buds occurs within a month of formation, often on terminal buds.

In winter the fungus lies dormant until spring and is protected from winter fungicide application while bud is closed. Infections can be spotted during winter pruning. Netting can also increase susceptibility due to increased humidity, Pink Lady and Gala varieties are also highly susceptible.

Management: In winter the fungus is dormant, if spotted on shoots and twigs prune immediately. This will reduce the number of infected buds at budburst, the infected shoots were already of compromised quality. Monitor through spring for white fluffy growth on soft new shoots and flowers as soft new leaves are susceptible to damage.

If you suspect significant overwintering infections, begin control at green tip. Oil based controls should be avoided at flowering as they can burn or cause fruit russet. Look for products targeting powdery mildew that also suppress alternaria for added benefit.

For more information, images, or management of other pests and diseases, visit the IPDM handbook LINK

Alternaria spp

Alternaria fruit spot or leaf blotch targets wounds and can occur after mite damage, windy or rough conditions. Fungus can carry over on overwintering leaves, but also bark and twigs. Gala and Pink Lady varieties are also highly susceptible. Reduce inoculum in winter by mulching fallen leaves, and remove any hanging fruit. Be mindful that even if weather conditions do not favour apple scab/black spot, alternaria can persist.

Leaf spots are distinctive as they start purple, may die off in the middle when expanding, and will form flat edges if they hit a leaf vein. Alternaria tends not to infect fruit until there is a high load on the leaf and branches. The main problem caused by alternaria is leaf drop and reduced efficiency of the tree.

If infecting fruit, spots on the skin are sunken and will worsen after storage, the fungus can also infect the wash water in packing sheds.

Management: occurs mainly in spring. Spores can survive for 6 weeks but may also lie dormant, waiting for the right weather conditions. Scout for infected leaves in the tops and inside tree canopies in late spring; warm, wet weather favours the fungus. If there was a high infection in the previous season, apply fungicide after harvest and at bud burst in spring to clean the canopy of any residues. Once symptoms occur, treatment becomes difficult.