Shot hole

Description

Affected leaves develop reddish spots, which enlarge forming tan centres and purplish margins, the centres eventually fall out giving the leaf a ‘shot hole’ appearance. This symptom is commonly seen in several other diseases, however shot hole lesions can be distinguished from other diseases by the presence of tiny, black, spore-forming structures in the tan centre.

Twig lesions, like leaves, begin as red spots which enlarge and turn tan with a purplish margin. Black spore-forming structures are present and cankers can form. Infected buds turn black and sometimes ooze gum and the tissues beneath the bud also darken. Fruit lesions are similar in appearance to leaf and twig lesions except for the absence of black spore-forming structures and the lesions become raised and form areas of dry scabby tissue.

The spores survive over summer on infected buds and twig cankers. Rain in autumn activates the fungus causing the release of spores known as conidia and these infect dormant buds and twigs during winter. As new growth emerges in spring it becomes infected and disease symptoms develop.

Control

Once established in an orchard, shot hole can be difficult to overcome, therefore a combination of cultural and chemical control tactics should be employed. During dormancy, infected wood should be pruned and destroyed. Prolonged wet conditions are favourable for shot hole to establish, therefore overhead watering should be avoided.

Promoting early leaf fall may reduce inoculum levels and therefore can be helpful in the control of shot hole. Where shot hole has previously been an issue, an application of lime sulfur during bud dormancy may also reduce inoculum levels.

Protective fungicide sprays used to control brown rot and leaf curl will often also be effective on shot hole. Trees should be monitored and where shot hole is present, particularly with the presence of spore-forming bodies in autumn, a protective fungicide spray should be applied so that buds are protected through to shuck fall. If lesions with black spore-forming bodies appear and rain is likely, a fungicide should also be applied.

Blue Shield^® and Luna^® Sensation^® can be used to manage shot hole.  Blue shield is registered for control of shot hole in stone fruit (apricots, cherries, nectarines, peaches, plums) and almonds. Luna Sensation is registered for control of shot hole in almonds and stone fruit. 

References