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Shot hole Infection on peach and nectarines

Shot hole is caused by the fungal pathogen Wilsonmyces carpophilus (formerly known as Stigmina carpophila).

Most commonly affected are apricot, peach and nectarines,  but the disease occurrs on all stone fruit.

The fungus is able to infect all stages of the plant;  the leaves, the twigs , the blossom and fruits.

Symptoms

Infected leaves show small brown spots with reddish margins (about 1 mm diameter), these spots expand to larger circular lesions (about 3mm diameter).  These spots dry and fall out of the leaf, giving a "shothole appearance". The infected twigs show clear- cut brown margins with a negrotic center, which does not drop out, but ooze large amounts of gum. Further on lignification of infected twings is hindered and the lesions will grow into cankers. In severe cases premature defoliation of the tree may result.

Fruits show firstly small circular, deep purple spots. As the disease progresses, the symptoms differ according to fruit type. On apricots the spots become brown, raised and rough, giving the fruit a scabby surface. On peaches and nectarines the scabs develop into deep indentations. Infected fruits have spots of gum and in severe cases cracks in the skin. 

The fungul pathogen overwinters in infected buds and cancers on twigs and branches.

It is able to infect leaves, stems and fruits during cold, rainy weather periodes in spring and autumn. Rain periodes to infect healthy plant organs are needed. 

The fungus is able to persist several years in the cankers or buds of infected twigs. Whenever conditions are favourable it may continue to grow, even during winter time. In spring time the conidia are splashed by raind to flowers and yound leaves and infect them. In unfavourable periodes (dry conditions) the conidia are still viable for several months. Rain is necessary for dispersal and humid conditions are needed for germination. The fungus is able to grow above 2°C. 

In FieldClimate.com we calculate the Infection of the Shot hole disease in dependence of rain periods, leaf wetness, air temperature and relative humidity. The risk of a light, moderate and severe infection is determined (if a light infection is 100% the requirements for an infection of the disease in the field have been fulfilled).