24 Ball et al: The Appropriate Response Process in PHC THE APPROPRIATE RESPONSE PROCESS (ARP) AND ITS ROLE IN PLANT HEALTH CARE by John Ball, 1 John E. Lloyd, 2 and Daniel F. Marion 3 Abstract. Plant health care (PHC) is presented as a strategy for the professional care of ornamental landscapes. Plant health care incorporates plant care practices, including inte- grated pest management (IPM), into a comprehensive man- agement system. This system requires that the practitioner use information about the plant, the stressor, and the client when making management decisions. The appropriate re- sponse process (ARP) is introduced as a conceptual model of the PHC decision-making process. Plant health care (PHC) is an integrative plan for es- tablishing and sustaining the long-term performance of plants in managed landscapes. It incorporates landscape design, cultural practices, regular moni- toring, and integrated pest management with client input and education. It is applicable to a broad range of tree-related professions and may be performed at many levels of intensity. It applies equally to land- scape designers or architects preparing a plan, the contractor installing a landscape, or arborists main- taining an established landscape. However, the prac- titioner maintaining established landscapes may have a greater variety of investigative and treatment techniques at his or her disposal, particularly when managing high-value, mature trees. Plant health care can be applied by arborists managing residential and commercial properties where the client may be an individual property owner. Plant health care is also applicable in municipal and institutional settings where the client is more broadly defined as the city council or the general public. PHC LANDSCAPE PROGRAMS Plant health care practitioners monitor and maintain landscape plants in conjunction with evaluating the associated environment. In the ornamental land- scape, plant management involves maintaining plant performance through cultural practices, investigat- ing the landscape through diligent monitoring, and identifying and treating problems when they do oc- cur. The investigative component of plant health care is performed by an individual known as a moni- tor. In many companies, the monitor may also be involved in sales or other production activities. Few companies currently have an individual who func- tions solely as a monitor. In addition to inspecting and evaluating plants and stressors, the monitor's other responsibilities may include developing client reports and implementing treatments. Treatments are procedures or actions specific to a particular situ- ation, event, or plant. These may include, but are not limited to, pesticide applications, augmenting or conserving biological control agents of pests, and us- ing structural repair practices such as cabling and bracing. The monitor is not usually responsible for the application of all of these treatments. Generally the monitor's treatment activities are focused on tar- get application of chemical pesticides or the use of biological controls (Marion et al. 1990). Pruning, ca- bling, and other treatments—while they may be identified by the monitor—are usually applied by a separate crew or company. In PHC, treatments are initiated when a stressor is detected or anticipated. These treatments may be short-term or ongoing depending on the type, inten- sity, and duration of the stressor. However, treat- ments should not be applied merely at the request of a client or as insurance against possible, but insig- nificant, stressors. Treatments are an integral part of PHC and their intensity can be simple to highly var- ied and complex. Many plant problems are related to an improper match of the plant's requirements to the site condi- tions or to alteration in plant appearance. However, solutions to these types of problems should not be limited to plant removal or client acceptance of the damage. Some problems may demand treatment when the only concern is appearance. The potential defoliation to a client's crabapple from apple scab may not justify treatment from the standpoint of plant vi- tality, but it may from the standpoint of appearance. The mature crabapple may be the central focal point of the landscape. Plant removal or acceptance of dam- age is not a realistic option for such a client. People