The flesh of the peaches becomes brown at the point where growth has manifested. At first the lesions are small, brown spots, with no superficial fungal growth which expands under favourable conditions. The lesions are categorised as firm and leathery. Monilinia laxa is the causal pathogen of fruit decay, but also blossom blight.
Spore masses of a tan / light-brown colour, often in the form of tufts / clusters, appear in concentric rings, as the fungus progresses in the host tissue. The skin of the infected fruit does not readily slip away when one’s finger is slid across the lesion. The skin of infected peaches may darken during storage, hence the reference to ‘brown rot’. Spread of decay to adjacent fruit is common.