Mississippi Turfgrass - Spring 2017

Page 14

Golf course notes

The Time for

Scouting

Turfgrass Diseases

Is During Spring Greenup... Or, in Other Words, Now!

By Maria Tomaso-Peterson, Ph.D., Associate Professor, Mississippi State University

In

Mississippi, spring greenup occurs during the period between the March equinox and the June solstice. When the turfgrass is transitioning from winter dormancy to spring greenup, what diseases might we expect to encounter? The answer depends upon the turfgrass species, the management regime, the environmental conditions and the diseases that were active the previous year. The disease triangle sums up the previous questions the turf manager may ask: host (turf species), environment (temperature, rainfall, management regime) and pathogen (previous diseases and any unexpected newcomers). A fourth factor, TIME, may not always be on your side (Rolling Stones, 1964) but instead on the side of disease development. To get a jumpstart on your disease monitoring, a fundamental review of turf diseases will be presented here. When a turf manager or homeowner calls about a problem in the turf and they suspect a disease, in my training as a turfgrass pathologist, I ask the question, “What is the host (turf species)?” The answer then dictates the line of questioning and subsequent conversation to determine whether abiotic/ biotic agents of non-infectious diseases, or more importantly, biotic agents of infectious diseases, are the problem. So, you may ask, “What are biotic/

14 • Mississippi Turfgrass • Spring 2017

abiotic agents of non-infectious diseases?” We begin with the biotic or living, non-infectious agents. If the turf stand appears to have a “disease,” the damage may be due in large part to algae, black-layer, moss or insects. Algae, moss and weeds colonize areas of reduced turf density that may have been damaged due to insect feeding or abiotic agents of disease. Apparent chlorosis and necrosis on a putting green may be the result of black-layer, a physical condition resulting in a lack of oxygen and subsequent root dysfunction. Abiotic or non-living agents are classified under chemical, physical and mechanical conditions that make up the environment in which the plant is growing. The chemical conditions include pesticides, salts (animal urine), fertilizers, nutrient deficiencies and chemical spills. Mechanical conditions include mower injury, scalping, and leaf and crown bruising, as well as damage due to excessive traffic. Temperature extremes, water, snow or ice accumulation, shallow and/or poor quality soils, buried construction debris, soil compaction, thatch accumulation and competition from shrubs and trees constitute the physical agents of abiotic, non-infectious diseases. These conditions may be the underlying causes that predispose the turf to infectious diseases, most notably caused by fungi.

The following table lists the common diseases of warm-season turfgrasses that may be observed during spring greenup in Mississippi.

Pythium blight and leaf spot

Pythium blight and leaf spot may be confused, since both foliar diseases occur during spring greenup under similar environmental conditions, particularly on putting greens (Photo 1). Both diseases cause random areas of blighted turf that may initially appear very dark to black and turn necroticbrown over time. Both can exhibit streaking of blighted turf with the movement of water or mowers. The plant symptoms are distinctly different and can be used as a diagnostic feature (Photo 2). Plant symptoms of Pythium blight include irregular, black lesions that appear on all leaves. Leaf blight will occur, causing a wet-wilt appearance within the turf canopy. In contrast, plants affected with leaf spot will have lesions ranging from tiny pinpoint purplish-black on the second to third leaf with larger black lesions and blight on the older leaves. The leaf spot pathogen(s) attack the older senescing leaves, causing chlorosis and necrosis in the lower turf canopy. The first step in controlling Pythium blight and leaf spot is to get the disease identified. Fungicides that control


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