Why will frequent, deep irrigation not prevent disease?

• A. Too much irrigation stresses the turf by restricting oxygen to the root system
• B. It reduces leaf wetness
• C. It increases beneficial fungi
• D. It dilutes nutrients

Answer: (A)

Frequent, deep watering creates waterlogged soil, which limits oxygen in the root zone. Roots need oxygen to respire and function; when pore spaces are filled with water, root respiration drops, roots become stressed or die, and the plant’s defenses weaken. This stressed condition makes turf more susceptible to diseases, and many turf pathogens thrive in consistently wet soils (for example, certain soilborne fungi and water-maturated pathogens). So, instead of preventing disease, overwatering can actually promote disease by starving roots of oxygen and weakening the plant.

The other options don’t fit as the best reason: leaf wetness is typically increased by frequent irrigation (not reduced), which would favor foliar diseases rather than prevent them. While irrigation can influence microbial communities, simply increasing irrigation doesn’t reliably boost beneficial fungi. And while excessive irrigation can affect nutrient concentrations, the primary link to disease risk is the oxygen deprivation in the root zone, not nutrient dilution.