Answer: Pyracantha are subject to two diseases: scab and fire blight. But the symptoms you describe do not completely match the usual progression of either disease. Scab disease will leave lesions on the stems and fruit (similar to apple scab), but it would also affect leaves. Fire blight affects entire shoots, turning leaves a reddish-brown and leaving them hanging on the branch or stem. Both diseases would therefore show other symptoms besides the brown berries. Unless additional symptoms appear, it's possible the problem is cultural or environmental. Perhaps there was a cold snap that damaged the berries or an extended rainy period that prevented insects from pollinating the flowers.You might want to prune off the berry clusters and remove them from the garden -- just in case it is a disease problem -- and then watch the plant closely to see if additional symptoms appear.
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