The answer to 'why is my fence disease' is that your fence may be suffering from a variety of issues, including rot, insect damage, or environmental factors. Common symptoms include warping, cracking, or discoloration of the wood. To address the problem, it's important to first identify the underlying cause.
If the issue is limited to a small section of the fence, you may be able to address it through DIY repairs, such as replacing damaged boards or treating the wood with a preservative. However, if the damage is more extensive or the cause is unclear, it's best to consult a professional landscaper or fence specialist. They can assess the condition of your fence, determine the root cause, and recommend the most effective solution to restore it to full health.