Role of Stress in Predisposing Trees to Insect Colonization: Implications for Plant Health Care

Plant health care is a program of preventive maintenance, based on the use of cultural, biological and chemical tactics, to enhance plant appearance, structure and vitality. Trees planted in the urban landscape are considered to be stressed and predisposed to successful colonization by many insects. This presumption that there is a simple index between vitality and stress, and that stressed trees are predisposed to colonization, may not always be true. The relationship between tree vitality and susceptibility to insect attack is highly complex. Tree susceptibility to insect colonization does not increase continuously with stress. Recent studies have indicated that mild stress may improve tree defenses and that a plant health care strategy aimed at maintaining rapid tree growth may not reduce susceptibility to insects. Extension specialists and researchers need to focus their efforts on understanding tree defense strategies and developing cultural recommendations aimed at improving defenses rather than growth.