The answer to 'stone walkway brown patches' is that the most common causes are moss, algae, or fungal growth. These can develop on stone walkways due to moisture, poor drainage, or lack of sunlight exposure. Symptoms include unsightly brown or discolored patches that make the walkway look unkempt.
To address this issue, you can try cleaning the walkway with a stiff brush and a mild detergent solution. This can help remove any surface growth. You can also apply a stone sealant or algaecide product to help prevent future growth. However, if the problem persists or the walkway has significant damage, it's best to call in a professional landscaper to assess the issue and provide a long-term solution.