You Are Here: Management Updates 2009 Archive July 30, 2009

Date: July 30, 2009
Category: Diseases
Subject: Algae, Black Layer

We are experiencing a different sort of summer stress period this year than the typical hot, dry summer weather. Extended periods of overcast weather and frequent, intense rain events are causing a lot of environmental stress on turfgrass. Many specimens submitted to the UMass Extension Plant Diagnostic Lab with the complaint of yellowing, declining turf (especially Poa annua), have no major turfgrass pathogens present that are responsible for the symptoms. Often, these specimens have abundant algae on the soil and turfgrass foliage. Several specimens have also exhibited a marked black layer.

Both alage and black layer are associated with overly wet soil. The algae reduce air exchange between the plant roots and the atmosphere, leading to root death. Algal growth can be controlled by improving soil drainage, revising irrigation procedures, and by increasing the penetration of sunlight through trees and shrubs. Blue-green algae are typically thought of as a secondary problem; they colonize areas of thin turf and impede recovery by creating a mat or thin crust on the soil surface and contribute to the formation of black layer. Application of dilute bleach solutions, copper sulfate, and some fungicides (chlorothalonil, mancozeb) will control algae and aid in the recovery of the grass only when wet conditions are corrected.

Black layer is a physical condition of the soil associated with poor drainage, high water tables, and soil layering due to excessive thatch or poor compatibility between topdressing material and the underlying soil. Black layer is especially prevalent in substrates with high sand content. The major predisposing factor for black layer is anaerobic (oxygen deficient) conditions caused by excessive rainfall or irrigation, soil layering, and/or soil compaction. Under anaerobic conditions, sulfur in organic matter is converted by sulfate reducing bacteria to hydrogen sulfide gas which is directly toxic to turfgrass roots.

The black layer forms from the reaction of iron or other divalent cations to form a metal-sulfide precipitate. Blue-green algae may also contribute to the formation of black layer. Roots are killed by a combination of lack of oxygen, hydrogen sulfide, and the stress associated with anaerobiosis. Symptoms start as yellowing and bronzing of affected turf, particularly in low lying, shaded, or waterlogged soils. Eventually, the turf thins in an irregular pattern, dies, and turns brown. Black layer interferes with water infiltration and makes the anaerobic conditions worsen. The layer has a foul, sulfurous, rotten-egg odor.

Primary management of black layer consists of eliminating perched water tables and their underlying causes, and relieving the waterlogging which may be due to excessive irrigation, poor drainage, soil compaction, and/or soil layering. Frequent core or quadratine aerification, spiking, water injection aerification, and fans can help to alleviate anaerobic conditions. Physical barriers that restrict airflow, such as shrubs and tress, should be removed or pruned. Avoid applications of fertilizers, pesticides, and soil amendments with significant amounts of sulfur, iron, magnesium, manganese, or organic matter Water sources that are high in organic matter or alkaline (pH above 7.0) should be avoided (ponds, sewage effluent). Nitrate forms of fertilizer may help alleviate black layer, but they must be applied with care due to the likelihood of fertilizer burn. Increasing the mowing height reduces light penetration and can help reduce the formation of algal scums.

Submitted by: M. Bess Dicklow

DISCLAIMER - As always, it is the responsibility of the applicator to verify the registration status of any pesticide BEFORE applying it. Different states have different regulations as well. The author and the University of Massachusetts are not liable for any consequences of any pesticide "recommendations". Mention of any trade name is not to be considered endorsement of a product.

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