Each year, Floridians spend millions of dollars to protect their lawns and landscapes from the harmful effects of weeds, diseases, and insect pests that threaten ornamentals. And with good cause. As the global economy expands, the number of exotic pests introduced into this country also has increased. Some of these pests pose serious economic and environmental consequences. Recent examples include citrus canker, Asian cycad scale, pink hibiscus mealybug, and lobate lac scale. We remain vigilant for signs of oak wilt, red palm mite, and new strains of Fusarium oxysporum that may threaten our palms. In certain situations, we have learned that a pesticide may provide excellent control and is the key to resolving a difficult pest problem. In other situations, pesticides seem to provide little benefit. How can this be?

Down With Diseases
To answer that question, a grower or landscape manager must know what they are dealing with and that is where integrated pest management or IPM comes into play. Remember the disease triangle that many of us learned back in Plant Pathology 101? In order for a disease to be present, three things must occur: 1) a susceptible host; 2) a causal agent (e.g. a bacterium, a fungus, or a virus); and 3) environmental conditions favorable for infection and progression of the disease. Remove just one of these parameters and you will have no disease.

Pesticides typically work by suppressing or eliminating the causal agent component of this equation. In situations where a pesticide is extremely costly or provides only partial control, or where the pest may repeatedly reoccur and/or pest resistance is likely, it may be more effective and economical to address the environmental component of the equation.

Rotten Luck
Let’s take root rot for example. Most of the time, this problem occurs when a plant that requires good drainage is experiencing water-logged conditions. This could be due to its location in a depressional area where water frequently accumulates, or a landscape or production operation that is over-irrigated. Root rot also can occur when plants are planted too deeply, soils are compacted, or the growing medium does not drain sufficiently. Such conditions create an oxygen-depleted root zone that stresses the plant, making it more vulnerable to attack by root-rotting fungi that might be present in the soil.

While certain fungicides that might have activity against these organisms can be helpful, the fundamental problem will not be resolved until the environmental situation is corrected. This can only be done by reducing irrigation, lifting the rootball, relocating the plant to a better drained spot, and/or repotting with better draining media. Reliance on the fungicide alone really treats the symptoms but not the cause of the problem -- insufficient oxygen in the root zone.

IPM is based upon a fundamental understanding of the biology and management needs of both the plant species and the pest. Know your plant’s requirements for soil type and drainage, light regime, water, and nutrition. Become familiar with its unique signs of stress. Likewise, be able to recognize all stages of economically important pests that could become a problem and know how to manage them. Be aware of the whole arsenal of management options that may be available, including 1) sanitation, 2) good cultural practices, 3) mechanical controls, 4) biological controls, 5) resistant varieties, and 6) pesticides.

Sanitation Implementation
Sanitation in the landscape and nursery are crucial to preventing diseases from spreading. When in the landscape environment, always scout for diseases on leaves and branches. Make sure to remove all diseased plant material from the site.

In the nursery situation, the same holds true. When removing diseased plant material, make sure it is taken away from the nursery site on a daily basis. Decomposing plant material can become an excellent environment for fungal growth. When pruning out diseased plant material, always be sure to sanitize your pruning tool between each pruning cut.

Good Cultural Practices
Cultural practices include activities that go into growing a plant, including proper site selection, plant spacing, pruning, watering, and fertility. Good cultural controls will include preventing over-irrigation, monitoring leaf wetness periods, using soil media that provide good drainage, stepping-up trees at the correct depth to avoid deep planting in the container, and providing adequate levels of essential nutrients. By utilizing good cultural practices, you promote a healthy, vigorous plant that is much less susceptible to insect and disease pressure.

Mechanical Controls
Mechanical or physical control methods can involve the use of barriers, such as screening vents in greenhouses, trapping through the use of pheromones, or simply washing aphids off plants with a pressure hose. Through the use of mechanical controls, early plant diseases and insect infestations can be suppressed by simply hand removing the diseased or insect infested parts and disposing of them. Mechanical control is most effective and can be achieved in many instances when detected at early stages of pest infestation when populations are low.

Biological Controls
Biological control involves the use of natural enemies such as parasitic wasps, insect predators such as assassin bugs or lady beetles, and fungal pathogens. When using biological controls, the object is not to eradicate the pest but to suppress it to acceptable thresholds. As opposed to a general application of a pesticide, biological-control methods can be used to target specific pest problems.

Resistant Varieties
Incorporating host plant resistance (HPR) in the landscape can minimize damage caused by pests and viruses. Examples of HPR include roses that are resistant to black spot, and nematode-resistant rootstocks of Gardenia thunbergia. The goal of HPR is to make the plant less inviting for the pest, resulting in less plant damage.

Picking Pesticides
The use of pesticides is not prohibited in an IPM approach. However, when deciding to use a pesticide, consider it as a last resort and choose one that is both least toxic to the environment and will not harm the plant or cause build-up of other pests. Select the right pesticide for the job and only use a pesticide that has the plant and pest listed on the label. When applying a pesticide, use the recommended amount. By using too little pesticide, you might encounter pest control problems. Too much can injure the plant and present additional costs to the applicator. Remember to read the container label carefully for correct dosage rate and that “The label is the law.”

By carefully following the steps to an IPM approach, the applicator can systematically control pests effectively with little impact to both the earth’s environment and the applicator’s bottom line.

Michael Orfanedes and Ed Skvarch are commercial horticulture agents at the
University of Florida/Institute of Food and Agricultural Sciences.