April was a wet month in Indiana with rainfall totaling 2-10 inches more than normal in April for areas of Indiana (see precipitation map below). Heavy rainfall can cause flooding stress on turf. Flooding reduces oxygen to the plants from the soil and could ultimately lead to plant death without oxygen. If water saturation is only around the roots in the soil while shoots (leaves) are exposed to air, the damage to turf is much less than when plants are submerged under water. In addition, soil erosion and deposition, debris, and the accumulation of toxic substances can also kill turf following flooding events.
Plant survival depends on several factors: turfgrass species, submergence depth and duration, and water temperatures. When submersion occurs simultaneously with high temperatures, plants can die quickly due to a lack of the energy production to sustain plant growth. Plant survival can be either through fast growth to above the water to obtain oxygen or slow growth to reduce carbohydrate consumption. For common turf species, creeping bentgrass and bermudagrass are most tolerant of flooding. Kentucky bluegrass and tall fescue are fairly tolerant. Annual bluegrass, perennial ryegrass, and red fescue are least tolerant.
Turf discoloration and yellowing is a common symptom of flooding stress due to loss of chlorophyll and nitrogen uptake. Once water has receded, a light fertilizer application will help grass recovery. Soil cultivation improves the physical condition of soil and increases oxygen concentration to the roots, which will benefit the regrowth of the turf. Walk-mowing with lightweight equipment in moist or saturated soils will help reduce soil structure damage compared to heavier ride-on equipment.
Yiwei Jiang, Turfgrass Physiologist