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Stone Fruit scab Cladosporium carpophilum Model

Stone fruit scab is induced by the plant pathogenic fungus Cladosporium carpophilum. The pathogen occurrs on peaches, nectarines, apricots and plums, while losses are generally greater on peaches than on the other fruits.

The disease affects twigs, leaves and fruits. The most serious damage results from fruit infections.

Symptoms

Fruit lesions start as small, round, greenish spots. These spots generally don't appear until the fruit is half grown even though infection occurred earlier in the season (about six to seven weeks after petal fall). Older lesions are approximately 1/4 inch in diameter and develop a dusty or velvety green appearance. The numerous lesions typically are clustered near the stem end of the fruit (this site is exposed to the sun). Extensive spotting can result in fruit cracks, which serve as entrance points for several fruit rotting fungi. Fruits may also drop prematurely or could not be stored well.

Leaves could also be infected. Small, round and yellowish- green spots occurr on the undersite of the leaf. The plant tissue may dry und drop down, leaving shot- holes. In a rainy season the infected leaves usually drop early.

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On twigs cankers begin as small, reddish lesions on current season's growth. These cankers expand slowly and may not be visible until mid summer. The small cankers have irregular margins, but do not cause sunken areas on the bark.

On the twigs the mycelium (or conidia) hibernates in the form of dark-brown spherical cells. From overwintering mycelium, conidia are produced in the spring, and the latter are carried to the leaves and fruits by wind or by rain. The conditions which favor disease development are temperatures above 16°C for spore production, over 10°C (optimal 22°C to 27°C) for spore germination, and between2°C and 35°C for disease development. Germination and penetration into the plant tissue follows shortly.  Inoculations and infections continue to take place until about one month before the fruit matures. As the fungus grows on the fruit the mycelium attaches itself closely to the surface between the hairs, forming a mat of short, plump cells which give rise to conidiophores and conidia. The flesh of the peach is not penetrated, but the close contact of the fungus with the outer cells allows absorption of nutrition from the fruit through the unbroken walls. Evidently there is some injury to the outer cells.

In FieldClimate the risk of a Caldosporium carpophilum infection is determined by wet conditions during spring and early summer after petal fall. The disease is usually more serious in low- lying, shady and moist areas with low air movement.

In FieldClimate.com we determine infections within a temperature range of 7 to 24°C, with a temperature optimum around 20°C.

The fieldclimate Modell calculates in dependence of leaf wetness duration and temperature a risk model of Cladosporium carpohilum.