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All images courtesy Tom Hsiang PLANT DEFENCE ACTIVATORS Controlling Turfgrass Disease By Tom Hsiang, PhD, Paul H. Goodwin, PhD, and Alejandra M. Cortes-Barco, M.Sc. P lants are known for their many natural defence mechanisms against stresses, including those caused by diseases. Unfortunately, under intensive plant maintenance systems, these natural mechanisms are often unable to guard against outbreaks without significant economic loss. However, there are chemicals that have been observed to stimulate the natural resistance pathways in plants, although most research has been conducted on broadleaf plants. These compounds generally do not have a direct antifungal activity, but act by triggering existing defence mechanisms of the plant. This article examines the role of these compounds in turfgrass. Activated resistance against plant diseases Activated, acquired, or induced resistance is a physiological state in which environmental, chemical, or biological stimuli increase a plant’s defences against subsequent pathogen or insect pest attack. During induced resistance, the activating agent— often called a ‘plant defence activator’— is recognized by the plant or stimulates a part of a recognition-signalling pathway. The pathway(s) eventually promote the expression of genes resulting in activation of defence mechanisms, such as production of antimicrobial proteins. 1 The enhanced resistance is expressed locally at the site of infection, or, in some cases, systemically throughout the plant. 2 24 January 2014 CG_Jan2014.indd 24 1/6/14 2:29 PM