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Symptoms and Signs

The brown rot fungi cause a blight of blossoms and twigs (Figure 2) and a soft decay of fruits of peaches (Figure 3), cherries (Figure 4), and plums (Figure 5). Thus, there are two distinct phases of this disease.

Figure 2	Figure 3	Figure 4
Figure 5	Figure 6	Figure 7

Blossom and twig blight

This phase of the disease occurs in early spring when the trees are blooming (Figures 6 & 7), although twig blight also can occur during the fruit rot phase. The anthers and pistil of the flower are infected initially (Figure 8). The fungus then invades the floral tube (Figure 9), the ovary, peduncle, and usually the twig to which the peduncle is attached (Figure 10). Infected blossoms wilt, turn brown, and usually cling to the twig. Extension of the infection into the peduncle and twig results in a necrotic area in the woody tissue termed a "canker" (Figure 10). Sometimes succulent twigs and shoots become infected directly when there are extended periods of both moisture and warm temperatures (20 to 28ºC, 68 to 82ºF).

Figure 8

Figure 9

Figure 10

Under moist or humid conditions, ash-gray-brown colored sporodochia (tufts of conidiophores) bearing conidia (asexual spores) form on the surface of diseased blossoms and twigs (Figure 10). The presence of conidia is a diagnostic sign that separates brown rot from other fungal and bacterial diseases of stone fruits. A gummy substance usually exudes from the cankers, causing the blighted flowers to adhere to the twig.

Fruit rot

Fruit susceptibility to brown rot increases during the 2 to 3 week period prior to harvest. Increased susceptibility is associated with an increase in sugar content as the fruits ripen. Initially, tan-brown, circular spots are visible on the fruit (Figure 11). Under humid conditions, ash-gray-brown masses of conidia develop on these lesions. There can be thousands of conidia on a lesion, each potentially capable of initiating a new infection. If environmental conditions are wet and warm during fruit ripening, the entire crop can literally be destroyed"overnight" (Figure 12).

Figure 11

Figure 12

Diseased fruit that do not fall to the ground dehydrate and become shriveled "mummies" that cling to the branch (Figure 13). Sometimes the fungal infection extends from the fruit into the twig and branch (Figure 14). Although not common, brown rot also can occur on ripe apples and pears.

Figure 13

Figure 14

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