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Plant Health Care

By Marlene Lyons, Transfer Master Gardener



As gardeners, most of us remember a time when pesticides had a prominent place in our arsenals of remedies used to protect our flowers, shrubs, trees, and vegetables from the ravages of pests.  Although many of us have moved on, unfortunately, it is not uncommon to come across posted warnings on lawns of friends and neighbors alerting us to the possible health consequences of newly applied pesticides used to keep lawns emerald green and fruits and flowers picture perfect.

As with all things, new information pushes us to acknowledge the sometime negative consequences of our behaviors, and through both public discourse and private experience, we are motivated to change our ways.  Perhaps you were shocked into change after reading Silent Spring (Carson, 1962) or just experienced a slight awareness that birds or bees, or other insects (who were not yet labeled as “beneficials”) were not as plentiful in your garden as you once remembered.


Whatever the impetus, many in the garden community said “Enough!” and took it upon themselves, through coursework and/or self-study, to find new ways to produce and maintain plants and gardens using a healthier, more holistic approach. Fortunately, researchers at universities, extension services, and botanical gardens were collecting and analyzing data to document the limitations and negative effects of pesticides and experimenting with alternative processes that could be used to contain (within reason) damage done to plants and gardens.  One such process was Integrated Pest Management.

IPM is an approach to pest management this is informed by economic, social, ecological and environmental considerations.  It includes cultural, physical, biological and chemical measures to suppress pests below thresholds at which they cause unacceptable damage. By definition, IPM is NOT a total biological program, a total organic program nor is it a no-pesticide program (Flint and Van den Bosch, 1981).   It is neither the least nor most expensive method of pest control (although it tends toward the more expensive).  IPM is a flexible decision-making process that requires that the user have knowledge of plants, their inter-connections with their cultural environments, and the strengths and limitations of most common interventions. 


The basic components of IPM include:  1) Monitoring; 2) Setting thresholds; 3) Applying IPM strategies; and 4) Evaluation.  IPM is not intended to eradicate all pests.  It maximizes natural controls and is an integrative approach using multiple control tactics.  Intervention occurs only when necessary, and management procedures may produce unexpected/undesired side effects (Olkowski and Daar, 1991).


Successful control of garden pests is dependent on many factors, the most important being correct identification of the plant, correct identification of the pest, and appropriate timing of the intervention or treatment.  Therefore, IPM requires its user to have a working knowledge of plants and the ability to observe and manipulate the environment.  For example, the user must be able not only to correctly identify the plant, but also know what a healthy specimen looks like in order to observe deviations from the norm. 


Monitoring is the cornerstone of IPM.  It drives the IPM process and provides input to the decision making component of the process.  Monitoring allows for early detection, can pinpoint pest location, and helps to determine treatment timing.  In addition, monitoring can identify key plants, (obvious indicator plants that are predisposed to pest problems) key pests and key locations.  It can recognize changes in pest populations over time, identify beneficial control agent populations and pinpoint their activity.  In addition, monitoring provides data for control recommendations and evaluation of the effectiveness of those controls.


IPM seeks long term, sustainable solutions and looks to solve problems with multiple strategies. (EPA, 1993). Those strategies include physical controls (sanitation, pruning, pest removal), horticultural controls (pH, fertility, light, water, temperature, soil structure, site appropriate planting), biological controls (use of beneficials, conservation recognition, soil augmentation), and chemical controls Adams, 1996).


The IPM process, however, is reactive in nature, and that has led to another iteration called Plant Health Care (PHC). PHC is a science-based concept that requires management, observation, and manipulation of plants.  PHC dovetails and works with IPM to strengthen significantly the focus on PROBLEM PREVENTION.  While it includes and builds upon IPM, it is not a replacement for it (Cook, 2000).


The goal of PHC is to grow healthier plants with fewer problems through a comprehensive plan including appropriate plant and site selection, proper planting and proper cultural care.  Cultural problems arise from external factors that directly limit plant function as well as predispose the plant to pest problems – site selection being the most important.


The plant and its requirements become the central focus of plant care rather than responding to symptoms caused by pest presence, physical agents, or nutritional deficiencies.  Data collected through monitoring and recorded observations are analyzed to predict when plants are most susceptible to pests and when pests are most vulnerable to treatment. (Ascerno, M.E., 1991)


In addition to routine plant inspection and cultural observations, calendar approximation; calculation of Growing Degree Days (GDD), and correlation of pest development with Plant Phenology (PPI) are some of the techniques used to predict pest activity (UMass Extension, 2014).  The Calendar Method is based on historical data and past experience and is expressed as an approximate date on which pests should appear.  GDD is a measure of the amount of heat that accumulates above a specified base temperature during a 24-hour period (Gibson, 2003).


Plant Phenology Indicators (PPI) is the third alternative timing tactic.  Phenology is the study of recurring biological phenomena and their relationship to weather (Herms, 2004, p. 50).  Since plant development is temperature dependent, plant phenological events can be used to track degree-day accumulation and predict insect activity.  Based on data collected across the U.S., biological calendars consisting of the flowering sequence of ornamental trees and shrubs can be used to track degree-day accumulation and predict pest activity.  (Herms, 2004).  Since insects are more active in warmer temperatures and less active when temperatures are cooler, their development is strongly driven by temperature. The direct relationship between insect development and weather (insect phenology) is also a precise method to establish treatment timing  (Ascerno, 1991).


How are these data useful? Let me present an example. Based on these timing strategies, we know from the Calendar method that the Eastern Tent Caterpillar eggs hatched on May 6 in 2014.  The GDD calculation shows that 92 GDD’s are required for egg hatch. If the temperatures are abnormally warmer or colder than they were in 2014, it is then necessary to consult the GDD chart ( ( to determine how much sooner or later than May 6 we should expect egg hatch.  Based on these data, we know when to start looking for this pest in our ornamental trees and take appropriate action to remove them.


Our gardens provide a classroom in which we can gain a better understanding of our interrelationships with the environment; we would be well served to observe and incorporate those lessons.



Adams, R.G.  1996.  Introduction to Integrated Pest Management. pp. 1-7.  In: Northeast Sweet Corn Production and Integrated Pest management manual, [R.A. Adams and J.C. Clark (eds.)], Cooperative Extension System, University of Connecticut.


Ascerno, M.E.  “Insect Phenology and Integrated Pest Management.”  Journal of Arboriculture, 17(1): 1991.


Carson, Rachel.  1962.  Silent spring.  Houghton Mifflin Co.  Boston, MA.


Cook, R.J.  “Advances in Plant Health Management in the Twentieth Century,” Annual Review of Phytopathology 38 (2000): 95-116.


Environmental Protection Agency.  1993.  EPA for Your Information.  Prevention, Pesticides and Toxic Substances (H7506C). 


Gibson. (2003).  Argonomy 212, Grain and Forage Crops.


Herms, D.A.  2004.  Using degree-days and plant phenology to predict pest activity.  In V. Krischik and J. Davidson, eds. IPM (Integrated Pest Management) of Midwest Landscapes, pp. 49-59.


Olkowski, W., and Daar, S.  1991.  Common sense pest control.  Taunton Press.  Newtown, CT. 


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