Shot hole disease (also called Coryneum blight) is a serious fungal disease that creates BB-sized holes in leaves, rough areas on fruit, and concentric lesions on branches. The pathogen that causes shot hole disease is '' Wilsonomyces carpophilus''.

Hosts and symptoms

The fungal pathogen ''Wilsonomyces carpophilus'' affects members of the '' Prunus'' genera. Almond, apricot, nectarine, peach, prune and cherry trees can be affected. Both edible and ornamental varieties are vulnerable to infection. Almost all over-ground parts of the plants are affected including the fruits, buds and the stems, but the damage is most noticeable on the leaves. The symptoms begin with small (1/10-1/4”) reddish or purplish-brown spots with light green or yellow ring around them. As the disease progresses the damaged areas become slightly larger and then dry up and fall away, leaving BB-sized holes behind. As the fungus spreads, more leaf tissue is damaged until the leaf falls. Significant infections can reduce the amount of photosynthesis that can occur, weakening the plant, and decreasing fruit production. The infection on the fruits in turn begins as small purple spots that develop into gray to white lesions. Gummosis may occur (both on the fruits and the stems as well). These lesions leave toughened spots on the skin, and in some cases the fruit may be lost. Infected buds may appear darker than normal. Branches may develop concentric lesions when infected. These lesions may girdle a twig and kill it.

Disease cycle

''W. carpophilus'' overwinters in infected buds and in twig

canker A plant canker is a small area of dead tissue, which grows slowly, often over years. Some cankers are of only minor consequence, but others are ultimately lethal and therefore can have major economic implications for agriculture and horticultur ...

s. Asexual spores (

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

) are dispersed in spring when moisture levels increase or as a result of overhead watering. Spores are pigmented and remain viable, in a dormant state, for months. Infection can occur any time moisture is present for at least 24 hours, as long as temperatures are above . At higher temperatures, infection occurs more quickly. ''W. carpophilus'' infection takes only 6 hours at .

Management

''W. carpophilus'' can remain viable for several months and spores are often airborne. Since the fungi thrive in wet conditions, overhead watering should be avoided. Remove and dispose of any infected buds, leaves, fruit and twigs. In fall, fixed copper or

Bordeaux mixture Bordeaux mixture (also called ''Bordo Mix'') is a mixture of copper(II) sulphate (CuSO4) and quicklime ( Ca O) used as a fungicide. It is used in vineyards, fruit-farms and gardens to prevent infestations of downy mildew, powdery mildew and other ...

can be applied.

Importance

Shot hole disease is a major concern of the stone fruit industry. It is estimated that 80% of the

California almond California produces 80% of the world's almonds and 100% of the United States commercial supply. Although almonds are not native to California, a hot, dry Mediterranean climate and developed water infrastructure create favorable conditions for co ...

crop may be infested with shot hole disease, resulting in a potential yield loss of 50-75%. In the 1930s, it was found that applications of Bordeaux mixture reduces shot hole disease on peaches from 80% to 9%.

References

{{reflist Fungal tree pathogens and diseases Stone fruit tree diseases