Spring Technical Guide: PHC - Making Plant Health Care Work

Plant health care has become the buzzword in the landscape maintenance field. You will hear it discussed in a wide variety of settings from golf course superintendent meetings to gatherings of arborists and lawn care managers. But what is PHC and how does it differ from integrated pest management? And most important, how can PHC make landscape managers’ jobs easier and improve client satisfaction?

Plant health care is defined as a program of strategies or treatments to maintain or improve the appearance, structure and vitality of landscape plants within the expectations of the client. The goal of PHC is to keep plants healthy. It is proactive, managed care, with the focus on the plant’s and the client’s needs. Notice that the definition of plant health care includes the phrase “within the expectations of the client.”

Depending upon the landscape manager’s position, the client may be defined as specifically as a homeowner who contracts for lawn or tree care or more broadly defined as the people on our multi-family complex or institutional grounds. While plants are our patients, the bills are paid by their owners, our clients. How we manage a property depends upon the expectations of our clients and their confidence in our ability to provide an attractive landscape setting.

Remember, most clients are not interested in pest management. They are not paying landscape managers to control pests but to manage plants. Their expectations are that plants entrusted in our care will be healthy, with an attractive appearance, high vitality and strong structure.

DEFINING PHC. Appearance, structure and vitality are collectively referred to as plant health. Vitality is the ability of a plant to adapt to its environment. A vital plant is one that is able to gather enough resources, solar radiation, water and nutrients to support its many functions.

Plants do more than just grow. They use the products of photosynthesis, called photosynthates, to provide the energy to support many essential functions. These functions are grouped into five major categories: reproduction, maintenance, growth, storage and defense. However, plants do not have an unlimited supply of resources and must allocate energy to meet higher priority functions first. How we manage plants can alter their allocation of energy to these functions and either increase or decrease their vitality.

The general hierarchy of energy ranks maintenance first in priority. A plant must first allocate its energy resources to maintain the living cells it has already formed. This priority is sometimes forgotten by managers who add luxurious amounts of water and fertilizer to accelerate tree growth. While this increases the tree’s canopy, it will also increase the maintenance requirements — more parts for the tree to support.

If this abundant supply of resources is reduced, either through a change in management or environmental stresses such as drought, the tree responds by dying back. It cannot maintain its living cells with the reduced resource pool and will attempt to adjust its size to one it can support.

If the plant has acquired enough energy to support its maintenance needs, it will use the surplus to fuel growth. This growth, in both new leaves and new roots, increases the plant’s ability to gather resources, solar radiation, water and nutrients. While this growth increases the maintenance needs of the plant, it also allows the plant to explore new soil for water and minerals and air space for light. As long as growth is balanced, the leaves with the roots, the plant will gather more resources than are needed for maintenance. Once growth demands are met, surplus energy is allocated for storage.

All plants must have a “rainy day fund.” Some energy must be stored, usually in the form of starch, to allow the plant to renew growth in the spring. Plants can also call upon these reserves to survive stress episodes such as defoliation and flooding that can temporarily reduce the plant’s ability to meet its needs.

Reserves may also be drawn upon for defense. Plants are not dependent upon humans to protect them from pests. They have a very active defense system. Trees, shrubs and grasses have the ability to defend themselves from a wide array of insects and living pathogens through a variety of strategies. Leaves can become tougher in response to insect feeding. Allelochemicals (secondary plant compounds) can be produced to retard insect feeding or inhibit the development of living pathogens. But plants can only defend themselves if they acquire sufficient resources to allow them to develop these defenses.

One of the most important plant health care objectives is to ensure plants acquire sufficient resources to adequately meet all of their functions, including defense. However, a fast growth rate should not be equated with a strong defense system. Just as adding luxurious amounts of water and nutrients will increase the plant’s maintenance needs, it can also reduce its production of allelo-chemicals as surplus energy is used to fuel growth rather than storage or defense. Application of fertilizers beyond levels needed to correct deficiencies can increase growth, but can also reduce defenses and increase susceptibility to pest colonization. Again, the point of PHC is to manage the resources to improve the vitality of the plants.

While reproduction has been left last in this discussion, it is the highest priority for the plant. A plant will divert resources to meet its reproductive needs. Landscape contractors may be familiar with the phenomena of reduced tree growth following a heavy fruit crop. Since reproduction is a periodic event rather than continual, it is usually overshadowed by maintenance. However, the demands that reproduction can place on a plant’s resources are considered in a plant health care program.

For example, an interesting strategy proposed for managing Dutch elm disease is to spray elms to prevent a seed crop. The plant can then allocate this surplus energy for other functions, including defense.

LOOKING GOOD. Appearance is an important aspect of PHC and is the primary means by which our clients gauge our success managing the landscape. A plant may be considered unhealthy if the plant is partially defoliated or discolored. This client focus on appearance is unfortunate since most plants can withstand high levels of defoliation or foliage discoloration without a significant reduction in overall vitality.

If lawn and landscape managers were to concentrate their management on only plant vitality, many pest problems would no longer be considered problems. Appearance is, however, important to our clients, whether they are office building tenants or residential clients.

Surprisingly, most people can detect rather low levels of plant injury. Studies involving a wide variety of ornamental plants from cut flowers to shade trees have all shown similar results. People can generally detect 4 percent to 5 percent plant injury, whether it is discoloration in the lawn, defoliation in a tree or other plant abnormality. They would initiate control at 7 percent injury if they were asked to manage the problem. Most important, the average person will consider a plant with 10 percent injury to be ruined. They would not buy a plant with 10 percent injury from a flower shop or garden center, and they will be dissatisfied with the maintenance service being provided if this level of injury occurs on their lawn or trees.

Thus, an important aspect of the landscape manager’s job is to keep plant injury below 10 percent. Obviously this is not always possible, but in these situations managers should be able to explain why the injury was beyond their control.

GOOD BONES. Structure is the third characteristic of plant health. If a tree has a long crack or large cavity that may result in a tree failure, it cannot be considered healthy even if the appearance and vitality are excellent.

The same is true of a lawn, although the impact is different. Turf grasses that have been cut with a dull blade will have tattered leaves. This makes the lawn appear rough, and it increases susceptibility to several diseases. Managers must be concerned with managing the whole plant — appearance, structure and vitality — not just focusing their attention on pests.

Plant health care puts together all three characteristics and then manages them within the expectations of the clients. Plant health care makes use of a variety of strategies from design to installation to maintenance to fulfill this expectation.

DESIGNING FOR HEALTH. Designing so that the species requirements match site conditions or modifying the site to meet species requirements is an essential part of PHC. Design, along with installation, is the foundation upon which we conduct our maintenance programs. Many landscape managers, when faced with a declining tree or lawn, complain that the tree is wrong for the site or the site was not properly prepared for the turf. It is difficult to grow quality turf on 3 inches of soil just as it is nearly impossible to grow an attractive pin oak on a soil with a pH of 8.5. Unfortunately, these examples are real situations that managers face. If landscape managers were included in the design process, maintenance would become easier.

While plant health care includes design and installation strategies, the individual responsible for the care of the landscape must focus on maintenance. Clients do not usually take kindly to being told that plant removal and replanting are the only options for problems. They may accept removing a plant or two, but beyond that the landscape manager is expected to work with whatever plant material exists on the property.

The means at the landscape manager’s disposal include, but are not limited to, mowing, pruning, fertilizing, core aeration and IPM. Plant health care does not replace IPM, but incorporates it into these strategies to improve the appearance, structure and vitality of ornamental plants.

Treatments that landscape managers have available to them as part of integrated pest management strategies include cultur-al practices and chemical treatments aimed at managing pest problems. Chemical treatments include foliar applications, bark paint, soil injection and tree injection. In the PHC philosophy, the choice of which method to use is dependent upon three important variables: the plant, the stress and the client. Following is an example of the PHC philosophy for tree injection:

Tree injections are one of the more controversial areas of tree care. There is no question that such practices wound trees and that the chemicals injected into the tree may, in some cases, cause more injury than the injection wound itself. However, injections minimize exposure to nontarget organisms and they limit pesticide exposure to organisms feeding on or in the tree. Injections may also provide effective control of pests for months or longer. There will be situations where injections are appropriate as well as inappropriate. Determining if injection is appropriate in a specific situation requires the manager understands the plant, stress and client.

COMPLEX RELATIONSHIPS. The fundamental objective of PHC is managing the health of plants. But how can a manager care for a plant if he or she cannot identify it? How many people would continue to utilize a veterinarian that could not identify their pet? If the veterinarian confused our prized Chesapeake Bay retriever with a Siamese cat we would probably pack up the dog and walk away in disgust. But that happens every day in the landscape maintenance profession. There are many landscape managers who cannot identify the tree or turf grasses that are entrusted in their care. I know tree care managers that consider all evergreens as “some type of pine” and broadleaf trees as “some type of ash or maple.”

Why is it so important for landscape managers to be able to identify their patients? For the same reason it’s important for veterinarians; the patient determines the choice of treatments. Medication and procedures differ among animal species because of their different physiologies. The same is true for trees. Broadleaf trees have differences in their water transportation systems — some are ring-porous, while others are diffuse-porous.

While there are great differences among broadleaf trees, the difference between broadleaf trees and conifers is even more pronounced. Yet many managers view injection procedures as uniform regardless of the species. Using the same procedure to treat a white pine, a sugar maple and a bur oak is the equivalent of treating a dog, a cat and a cow the same way.

The stress must also be evaluated to determine if injection is an appropriate response, because plant problems are rarely related to a single stress agent. Stress may reduce a tree’s vitality and increase its susceptibility to colonizations by insects or living pathogens. Managing only one stress will not restore the plant’s health.

A good example is the relationship between bronze birch borer and birch dieback. The bronze birch borer is a serious pest of many birch species. It is, however, a secondary pest, only successfully colonizing already stressed trees. In many urban areas the primary stress is high summer temperatures, particularly in the rooting zone. Injecting the birch to kill the borer larvae, while effective, is not a complete solution to the birch dieback problem. The underlying stress must also be reduced, by mulching a portion of the rooting area or other means.

The client is another important variable in determining whether injection is an appropriate response to a problem. The client’s expectations must be clearly understood and given consideration in our treatment decisions. I once had a client who parked his Lamborghini beneath an elm tree in the front yard. The tree was colonized by a large aphid population that was raining honeydew upon the car. Sprays were not an option because of a pool nearby, and soil injections were not practical due to limited accessibility. An alterative at the time was trunk injection. I gave the client all the facts at my disposal, including the risks to the tree’s health, and let him make an informed decision.

Obviously one possible solution was to move the car or keep it covered. But if you owned a Lamborghini, would you park it where you could not see it? Of course, not all expectations can, or should, be met. Sometimes clients have unrealistic expectations about the effectiveness of treatments or they are unaware of possible side effects to the plants. In these situations, client education is important.

Plant health care is the basis for our care of the ornamental landscape. By balancing the needs of our patients, the plants, with those who have entrusted us with that care, our clients, we can create a landscape that maximizes the benefits for all. The profession we are in, the care of the landscape that surrounds our homes and provides so many benefits, is truly necessary work. It is up to all of us to see that we do it well for our patients and their owners.

The author is a professor of horticulture with South Dakota State University, Brookings, N.D.