The answer to 'weed control turning brown' is that the weeds are likely dying or dead due to successful weed control methods. This is a common sign that the weed killer or other treatment you've applied is working as intended. The weeds will turn brown and start to wither as the treatment takes effect.
This is a good indication that your weed control efforts are successful. However, it's important to continue monitoring the area and re-treating as needed to prevent new weed growth. Proper timing and consistent application of weed control products is key for long-term results.