Reports of damaged lawns have come into the Horticulture Extension office from all over Iowa this spring. Damage ranges from dead turf underneath trees to complete death of the lawn. The cause of damage varies from site to site.
To understand what caused the damage it is important to reflect back on the 1991 growing season. Most of Iowa experienced a very wet spring and early summer. Rains fell often enough, that it prevented many people from mowing on a timely basis. Foliar diseases were common during this time period. In midsummer, the rains ceased and the weather turned dry. Weakened lawns suffered additional stress from the dry conditions. Patch diseases, white grubs and greenbug aphids were also diagnosed on many sites in late summer and fall. In late October, the temperatures dropped sharply and ice and snow quickly followed. Many lawns that were weakened from various stresses during the growing season could have been severely injured by the record cold temperatures in early November.
Following are a list of potential problems that could have predisposed the turfgrass to damage.
- Wet spring weather. The excessive wet weather in the Spring of 1991 weakened many turfgrass plants. Turfgrass in shady sites, low areas and compacted soils were most affected. These areas are slow to dry out and contain relatively low soil oxygen levels. Affected lawns became chlorotic and grew poorly. This was attributed to waterlogged soils that prevented iron and nitrogen uptake by the turfgrass plants. Root systems were shallow and most likely never reestablished in the fall. Therefore, many poorly drained soils under trees and in open areas were injured in the fall by the October freeze. Fine leaf fescues that normally do well in dry, infertile soils performed very poorly in the ISU shade evaluation trials in 1991. Whereas, grasses that normally do well in wet shady areas, such as Sabre bluegrass, grew very well.
This type of damage will usually appear rough and uneven. Frost heaving of the soil most likely exposed the roots to the desiccating winter conditions. Overseeding the site will be necessary to reestablish the lawn. Select turfgrass species and cultivars that do well in wet soils. Kentucky bluegrass and perennial ryegrass will work well in the open areas, and Poa trivialis "Sabre" is recommended for shade.
- Lawn with excessive thatch. This is easily diagnosed because the sod will peel back at the soil-thatch interface. Highly maintained lawns are most likely to have a thatch problem. Lawns with a thick thatch layer (1/2 inch or greater) may have a majority of their roots growing in the thatch layer. Since thatch has a very low bulk density when compared to the soil, temperature extremes will be much greater in the thatch than in the soil. The plant crown and roots within the thatch layer exposed to the low fall temperatures were most likely damaged by low temperature stress.
This type of damage will appear widespread in the lawn, with a general browning of the entire area. It will be necessary to remove the dead sod before reseeding. Not doing so will result in poor establishment of the new seed.
- Dry fall conditions. Many turfgrass sites suffered from the dry weather in the fall. New fall seedings were especially susceptible to damage. If the turfgrass seedlings failed to mature before the October freeze, damage was likely. Perennial ryegrass, tall fescue and fine leaf fescues are species that were most susceptible to this type of injury. Spring overseeding will be necessary.
- Insect injury. There were many reports of infestations of white grubs and greenbug aphids last fall. White grub damage would most likely appear in the open lawn. The damaged sod should easily pull up out of the ground. Grub damage should have appeared prior to the October freeze. However, the freeze could have done further damage to the turfgrass. Greenbug aphids are a foliar feeding insect. If gone unchecked, they could have weakened the turf and predisposed it to death by freezing. Greenbug aphid damage is most likely to have occurred in shady areas of the lawn. Overseeding into the current sod is recommended.
For additional information on lawn renovation and establishment, refer to Pm-1055, Turfgrass Renovation, and Pm-1072, Establishing a Lawn from Seed.
This article originally appeared in the April 15, 1992 issue, pp. , 1992 issue, pp. 55-56.