Thatch Collapse: A Devastating Disease Need Not be Global in Impact
Occasionally I will write about a turf problem with not a lot of confidence. In the United States we might use the phrase "skating on thin ice" to describe something we are not all that sure about. One such topic is the disease "Thatch Collapse". In all honesty, I have only observed thatch collapse on a few occasions mainly in the United Kingdom and not at all in the United States. It may be that we may diagnose it as fairy ring, or summer patch.
However, thatch collapse is a concern in New Zealand, Southern Australia, and other cool oceanic climate regions. Thatch collapse is believed to occur when a basidiomycete fungus or fungi (fungi that are similar those that cause fairy ring) decompose the thatch down to the soil resulting in sunken areas. A sign of the fungi is mycelium within the thatch layer. Generally, the symptoms appear after an extended dry period followed by rain. Thatch collapse is most prevalent on soils that have a layered rootzone of thatch and soil (topdressing). In general, the most severe symptoms occur on thatch turf.
With the arrival of summer, it is important to manage the thatch layer in your putting greens and athletic fields. Not only to minimize the potential for thatch collapse, but also localized dry spots, anaerobic soil conditions, and restricted root systems, minimizing excessive thatch buildup is critical. To minimize the impact topdress frequently enough to minimize layering, and core cultivate and fill the holes with topdressing if needed.
Topdress Prior to Coring? The combination of coring and topdressing is commonly done by coring first, removing the cores and then topdressing to fill the holes. Recently, you may have noticed that on short cut turf like putting greens, that topdressing is done prior to coring. The idea behind this practice is by topdressing first you stabilize the surface which minimizes the turf being "pulled up" when the coring tine is removed from the core hole. If you are considering topdressing first prior to coring you must have a rootzone mix that meets your topdressing specifications, because the rootzone mix will be reincorporated back into the rootzone along with the top-dressing once the coring procedure is done.
Photograph: Topdressing prior to coring (photo courtesy of Darren Davis)