IPM: Plant Health Care

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Gardening and the Environment

Yard care and gardening practices may have positive or negative influence on human health and the neighborhood environment.  For example, a turf enhances the environment by:

  • Converting carbon dioxide into oxygen.
  • Increasing water infiltration into the soil.
  • Reducing surface runoff and erosion.
  • Reducing dust.
  • Providing a microecosystem that effectively breaks down pollutants.
  • Moderating summer temperatures.
  • Creating a pleasant “people” space.

On the other hand, lawn care practices negatively influence the environment when grass clippings are mowed or blown onto the street (water quality problem), when fertilizers are over-spread onto hard surfaces, and when the unwarranted use of pesticides occurs.

Several terms (such as Integrated Pest Management, Plant Health Care, Sustainable Farming/Gardening, Best Management Practices and Organic Gardening) are used to describe farming/garden management systems designed to help the farmers/gardener maximize positive effects and minimize negative effects.

Integrated Pest Management, IPM

Integrated Pest Management, IPM, incorporates a variety of pest management strategies, including cultural methods, mechanical methods, use of bionaturals, and use of organic and manufactured pesticides. Objectives include maintaining profitability, minimizing pest damage, health-related hazards, and environmental hazards.

Because insect and disease problems vary significantly from crop to crop, application of IPM principles is also crop specific. IPM techniques used in an alfalfa field (perennial crop), a wheat field (annual crop), an apple orchard (perennial crop with minimal tolerance for pest damage) and the landscape (site with multiple plant species and higher tolerance to pests) will be vastly different.

Plant Health Care, PHC

The term Plant Health Care, PHC, was coined by the International Society of Arboriculture to more clearly define IPM techniques as they apply to tree care and landscape maintenance.

PHC is a holistic approach to landscape management. The primary objective is to grow healthy plants, and in so doing minimize the effects of pests. Concepts of PHC include the following:

  • Healthy plants have fewer pests. – Many insect and disease problems only attack plants under stress. Minimizing stress prevents many common pests. For example, Cytospora fungus and most borers only attack trees under stress (primarily soil compaction and drought)

  • Healthy plants are more tolerant of pests. – For example, aphids on shade trees generally do not warrant management efforts. An important exception is that trees under water stress (dry soils, non-established root system, limited root spread) are intolerant of aphid feeding.

  • Plant needs change with stages in their life cycle. – A plants needs for irrigation, fertilizer, pruning, tolerance to pests, etc. continually change through the growth cycles of the plant. In PHC, cultural practices change relating to the life cycle.

  • Problems arise from a combination of stress factors. – For example, over-mature forest coupled with drought leads to bark beetles in Western pine forests. Soil compaction and drought leads to Cytospora. This concept is known as the PIC cycle.

The PIC Cycle

A basic principle of PHC is recognition that plant problems generally arise from a combination of stress factors. This concept is called the PIC cycle.

Predisposing factors reduce a plant’s tolerance to stress. These factors should be considered in plant selection. Examples of predisposing factors include:

  • Planting trees in a site where root spread will be restricted due to soil compaction or hardscape features.
  • Planting trees intolerant of wet soils (like crabapples) in heavily irrigated lawns (leads to root rots).
  • Planting trees susceptible to iron chlorosis in soils with free lime.
  • Failure to structurally train a young trees (leads to storm damage).

Inciting factors include primary insect, disease, and abiotic disorders that attack a healthy plants causing acute stress. Examples include:

  • Soil compaction, the most common stress factor in the landscape setting.
  • Planting trees too deep (leads to trunk girdling roots).
  • Drought.
  • Leaf chewing insects, such as caterpillars and sawfly larva.
  • Leaf sucking insects, such as aphids, scale and leafhoppers.
  • Bark damage from lawn mowers.
  • Bark cankers and frost cracks from rapid winter temperature changes coupled with winter drought.

Contributing factors include secondary insect, disease and abiotic disorders that attack plants already under stress. They often lead to the plant’s death and frequently cannot be controlled. Examples include:

  • Bark beetles and borers (secondary to soil compaction, drought and wind damage).
  • Cytospora fungus (secondary to soil compaction, drought and restricted rooting system).
  • Trunk girdling roots (from planting trees too deep).

Management of contributing factors typically needs to be directed at the predisposing and inciting factors that stress the plant.

PHC Techniques

Examples of techniques used in PHC include the following:

  • Plant selection: Right Plant, Right Place – For the site, select plants to minimize future stress issues.

  • Soils management – 80% of all landscape plant problems relate to soil conditions.

  • Soil compaction (low soil oxygen and poor drainage).
  • Drainage.
  • Improve soils tilth with routine applications of organic matter.
  • Nutrient (fertilizer) management.

  • Water / Irrigation

  • The water requirement for plants to survive compared to the water needs for plants to grow may be vastly different.
  • Plant tolerance to wet (wetland plants) or dry (xeric plants) conditions.
  • Iron chlorosis is a issue of chronic over-watering.

  • Size and growth

  • Pest resistance and common pest

  • Cultural care

  • Planting dates
  • Varieties
  • Irrigation management
  • Spacing
  • Exposure to sun and wind
  • Plant species diversity
  • Mulching
  • Pruning

  • Weather influence on plant growth and pest potential

  • Temperatures
  • Wind and rain
  • Timing of insect activity

  • Mechanical methods to manage pests

  • Covers and barriers
  • Traps

  • Bionaturals for managing pests – Use of predators, parasites, disease organisms, and beneficial nematodes

  • Preservation is taking steps to preservation predators and parasites naturally occurring.
  • Importation is the purchase and release of predators and parasites.

  • Pesticides

  • “Organic”
  • Synthetic or manufactured

Pest Management Questions

As part of PHC, ask the following questions to guide pest management:

  1. What is the plant? Correctly identifying the plant will shorten the list of potential insects, diseases, or abiotic disorders.

  2. What is the disorder/pest? Correctly identifying the disorder/pest will set direction for effective management options. Gardeners often fail to control pests because they have misidentified the problems and are applying ineffective management techniques.

  3. What type of damage/stress does it cause? In the landscape setting, most insect and disease problems are only cosmetic and may not warrant management efforts. To protect the plant health, management may be needed on some pests . On fruits and vegetables, tolerance to insects and diseases is typically low.

  4. Under what situations will management efforts be warranted?

    In production agriculture, economic thresholds determine how much damage can be tolerated before it becomes economically feasible to treat. For example, this may be determined by counting the number of insects per leaf, number of insects in a square foot of soil, or the percent of leaves infected.

    In landscape horticulture, aesthetic thresholds characterize a relative level of cosmetic damage that can be tolerated before treatment is warranted. This threshold will vary considerably from individual to individual and from location to location.

    Spider mites are an example of a common pest generally kept in bounds by Mother Nature. However management efforts may be warranted in situation where mite populations explode due to hot weather, drought, dust on the plants (interferes with activity of beneficials) or the use of some insecticides including imidacloprid (Merit) and carbaryl (Sevin).

  5. What management options are effective on the pest and when are they applied?
  • Weather – While we do not control the weather, it directly influences the occurrence of many insects and diseases.
  • Cultural - such as watering more or less
  • Mechanical - Such as washing down the plant with a forceful stream of water to wash off pests.
  • Bionaturals - Use of beneficial predators and parasites
  • Pesticides - Including “organic” and manufactured

Life Cycle of a Plant

Another key concept in PHC includes recognizing that the care of plants changes with various stages of growth. Failure to relate cultural practices to the life cycle often leads to reduced growth and confusion about appropriate cultural practices. Tables 1and 2 give an overview of the life cycle of trees.

Life cycle of a tree

1.   Nursery production
2.   Establishment phase
3.   Growth phase
4.   Maturity maintenance
5.   Decline phase

Life cycle of a vegetable (annual)

1.   Seed germination and emergence
2.   Seedling growth
3.   Growth
4.   Flowering and fruiting


Table 1 – Life Cycle of a Tree

Growth Phase

Growth Objectives

Change to Next Growth Phase

Nursery production

Top growth = selling price

Planting

Establishment

Root establishment.

When roots become established, length of annual twig growth significantly increases.

Growth

Period of canopy growth – Balance canopy growth with root growth limitations.

Growth slows as tree approaches mature size (for site limitations)

Maturity, maintenance

Canopy growth slows as tree matures – Balance canopy growth with root growth limitations.

Minimizing stress on aging trees prolongs tree life.

Decline

Minimize stress levels.

Death

 

Table 2 – Influence of Life Cycle on Cultural Practices for Trees

Growth Phase

Irrigation
Water Need

Fertilization

Pruning

Pest Tolerance

Nursery production

Water = Growth

Fertilizer pushes desirable top growth

Structural training desirable

LOW
Could impact sales.

Establishment

CRITICAL
Trees are under water stress due to the reduced rooting system.

None to very little as nitrogen pushes canopy growth at the expense of root growth

Heavy pruning slows root establishment.

LOW due to drought imposed by reduced root system.

Growth

Water = Growth
Good tolerance to short term drought. However, short term drought will slow growth.

IF other growth factors are not limiting, fertilization supports growth.

Structural training sets the tree’s structural integrity for life.

HIGH,
except under stress situations.

Maturity maintenance

Good tolerance to short-term drought. Severe drought leads to decline.

Need for fertilization reduces. Over fertilization could push out canopy growth that the roots cannot support in summer heat and wind.

Maturing trees that were structurally trained while young have minimal needs for pruning

HIGH,
except under stress situations.

Decline

Intolerant of drought.

Evaluate stress factors as fertilization can accelerate stress in some situations.

Pruning limited to cleaning (removal of dead wood). Do not remove healthy wood on stressed trees.

LOW,
pests could accelerate decline.


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Additional Information

CMG GardensNotes on Diagnostics

Books


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Author: David Whiting, Colorado State University Extension (retired). Artwork by David Whiting; used by permission.

  • CMG GardenNotes are available online at www.cmg.colostate.edu
  • Colorado Master Gardener/Colorado Gardener Certificate Training is made possible by a grant from the Colorado Garden Show, Inc.
  • Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating
  • Extension programs are available to all without discrimination.
  • Colorado Master Gardener LogoNo endorsements of products mentioned is intended nor is criticism implied of products not mentioned.
  • Copyright. 2003-14. Colorado Master Gardener Program, Colorado State University Extension. All Rights Reserved. CMG GardenNotes may be reproduced without change or additions, for nonprofit educational use.

Revised October 2014

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