Fall comes with a different set of property management practices. Everything from late season seeding, emerged and pre-emergent weed control operations, and new installs including sod and ornamentals are ongoing with milder weather conditions, often including more rainfall.
We are also on the cusp of leaf removal operations and irrigation winterization. In fact, some of the more stressed trees are dropping leaves now in Northeast Ohio. It is also in this period that turfgrasses are still actively growing and are quick to heal/repair any cultivation practices including de-thatching and aeration.
Thatch is the tightly intermingled layer of live and dead plant material which is located directly at the base of the plant and above the soil. Thatch is comprised of stems, roots, and some leaf material which break down much more slowly and can form a spongy mat on the soil surface.
Thatch is a very natural occurrence, and thin layers can be beneficial in many circumstances. Buildup of thatch is more rapid on high-maintenance lawns than low-maintenance ones. The reasoning is that moderate to excessive use of nitrogen fertilizers will cause more growth of above ground material. Use of some fungicides and insecticides can reduce soil microbial activity responsible for the natural degradation of these organic components.
Certain species are also more apt to thatch accumulation. Cool season culprits include creeping bentgrasses and Kentucky bluegrasses which tend to build thatch layers more quickly whereas fine leaf fescues, ryegrasses, and tall fescues usually will be much slower.
In warm season species, hybrid bermudagrasses tend to produce thatch very quickly and zoysia is notably less rapid due to its slower growth rate. Generally, those species that readily grow stolons and rhizomes are more likely to develop mats of thatch.
There are some positives though. At light to moderate depth, thatch can protect plant crowns from traffic and temperature extremes. It can also help moderate soil moisture and temperature. On sports fields, it can have a cushioning effect protecting from some injury. This moderate depth is defined as less than 0.5 inches.
Thatch accumulation is said to be excessive once that layer measures over 0.5 inches and the detrimental effects can begin. Those negative impacts include reduction in drought tolerance, increased instance of localized dry spot (LDS) due to hydrophobic conditions, slower water and nutrient infiltration, and impaired gas exchange.
Excessive thatch can also lead to the risk of winter kill and can enhance spring dead spot activity. What’s more is that thatch can impede pesticide penetration to the soil where it is taken up by roots. Some products have a great affinity for organic matter and can become bound and rendered ineffective in thatch layers. Imidacloprid, for one, can easily be bound up and many pre-emergent herbicides become much less effective when the thatch layer is thicker.
Lastly, mats of organic materials provide a safe hiding spot for harmful insects and disease pathogens.