What environmental factor increases the susceptibility of grass to brown patch?

The factor that increases the susceptibility of grass to brown patch is high nitrogen levels. When grass receives excessive nitrogen, particularly in the form of fertilizers, it promotes lush, rapid growth. This can create a favorable environment for brown patch disease, which thrives in conditions where the grass is overly fertile and dense. The dense growth can lead to poor air circulation within the grass canopy, trapping moisture and creating an ideal habitat for the pathogens that cause brown patch.

Furthermore, high nitrogen levels can weaken the plant's overall health, making it more vulnerable to diseases. Plants that are overstimulated by nitrogen often become more prone to various stresses, including fungal infections, as they may not have the necessary resilience to combat disease effectively.

In contrast, low soil pH, heavy clay soils, and high humidity during the day can influence stress levels and overall plant health, but they do not directly correlate with an increased susceptibility to brown patch in the same way that high nitrogen levels do. Heavy clay soils can lead to waterlogged conditions, while humidity alone might promote disease, it's the combination with the rapid growth driven by high nitrogen that most significantly elevates the risk of brown patch.