Heavy rains in the upper Midwest has caused severe flooding especially along rivers and streams. Golf courses that are located in areas prone to flooding have observed large areas being submerged. The question often arises to the impact of submersion on turfgrass health
Flooding injury as outlined by James B Beard in Turfgrass: Science and Culture) occurs through erosion, deposition of soil, salt and debris to the extent that the turf is killed, and through direct injury of the turfgrass from submersion.
Regarding submersion, injury is dependent on:
- Depth of flooding (leaf blades above water, plant more resistant to injury than totally submerged). Having leaf blades above or floating on top of the water is demonstrated when we often see stolons from creeping bentgrass (Agrostis stolonifera) extending from pond or stream banks into the water.
- Type of flooding (stagnant versus running water). Stagnant water is much more damaging. Pools of water that drain slowly and are relatively shallow produces an environment that is devoid of oxygen and higher temperatures.
- Repetition of flooding (more injury with repeated flooding). Turfgrass plants become less resistant to flooding as the frequency increases
- Physiological condition of plant. Dormant plants are generally more resistant than actively growing plants. Bermudagrass (Cynodon spp.) has excellent flood tolerance while the submersion tolerance of creeping bentgrass is good, and Kentucky bluegrass (Poa pratensis) and annual bluegrass (Poa annua) are fair.
- Temperature of water. The warmer the water temperature the likelihood for turf injury is higher. In studies done at Michigan State University, Drs. Jim Beard and David Martin looked at the submersion tolerance of four cool season turfgrasses. They found at 30C (86F) water temperature that turfgrass survival beyond 5 days was not high (creeping bentgrass was the only one that survived to any extent beyond 5 days compared to Poa pratensis, Poa annua, and fine fescue.
-When the experiment was done at 20C (68 F) survival percentages were higher for all of the turfgrasses with creeping bentgrass having a 60% survival rate after 30 days.
- Turfgrasses in general become more susceptible to flooding injury when exposed to multiple flooding events.
If you are in a situation where flooding has occurred do not allow the turf surface to become sealed with debris and particulates. For example, on putting greens as the water begins to recede (0.3 to 0.5 meters) hose loose sediment back into the receding water. Do not let the sediment try on the green. Once the green has dried, core cultivate the green aggressively to break any surface sealing that may have occurred from sediment deposit. Reseeding some areas might be required.
note: If reseeding is required, it may be wise to do a bioassay. A bioassay would consist of taking a cup cutter sample from the damaged area and planting a susceptible plant seeds in the soil profile. Tomato seeds are one bioassay plant that could be used. The purpose of the test is to determine if there is any chemicals or substances that have been deposited from the flooding that could impact seed germination (ex. herbicide deposition).