Overstory #23 - Pest Prevention through Ecological Design
Overstory #21 covered the advantages of biologically diverse farming systems, including a more balanced insect flora. This issue expands on this concept for establishing systems that are inherently less susceptible to insect pest problems.
Pest Prevention through Ecological Design
"An ounce of prevention is worth a pound of cure." --old adage
Native forest ecosystems in the tropics teem with insects that co-exist with thriving and productive plants. However, modern forestry and farming arranges plants in patterns of human design, usually large monocultures, which creates ecological imbalance. These plantings often give rise to high populations of "pest" insect species, who feed on concentrations of their food source and interfere with production. For over 60 years, a sophisticated arsenal of insecticides has been routinely employed in the attempt to control pest insect populations. However, insects evolve quickly, and become resistant to the poisons--and new insect pests appear regularly as agricultural trade globalizes. As a result, insecticide-based management tends to become increasingly expensive over time, as more and newer chemicals are developed. Many insecticides are not selective in their targets, and also eliminate predators of pests, which ultimately worsens the pest problem. After decades of all out warfare against insect pests, it is now apparent that fighting pests is a losing battle. It is time for a different approach entirely.
To Ponder: What are the long-term drawbacks of pest management based on insecticides?
A) An insecticide becomes increasingly expensive and decreasingly effective over time,
B) Insects evolve quickly and become immune,
C) Pesticides decimate natural predators (other insects as well as spiders, birds, frogs and other predators)
D) All of the above
The alternative is to develop carefully planned ecologically-based agricultural systems which are inherently less susceptible to attack by insect pests. Such systems minimize the necessity of reacting to pest infestations with intensive management practices. Instead, the system as a whole is designed and developed so that, like a natural ecosystem, pest populations are regulated through the checks and balances of nature. Ultimately, the need for human intervention to moderate insect populations is greatly reduced, and ideally even eliminated.
In this system, if and when serious pest problems appear, the judicial use of botanical pesticide products (like neem) and intensive pest management strategies like IPM (integrated pest management) are brought in as a last resort, and then only with the long-term goal of creating a healthy system with a naturally balanced population of pests and predators. [Below we include some references for integrated pest management (IPM), although the focus of the article is on setting up systems so that minimal IPM intervention is required.]
Pest prevention through ecologically based design is a complex subject that warrants more attention and research. There are thousands of different kinds of insect pests, and many complicated interactions between the structure of the landscape, the behavior of the species, and the connections between pests and their predators that should be better understood to maximize the effectiveness of this model. There are some general guidelines that are recognized as valuable, which are outlined below.
Two Keys to Pest Prevention
(1) Healthy plants
Keeping plants healthy is important to deterring pests, as healthy plants are less likely to be attacked. When a plant is stressed it is more susceptible to pest problems. Drought, injury, nutrient imbalances, and other factors can reduce a plant's ability to resist damage, just as a person who eats well and is in optimum health is more likely to withstand exposure to a virus than someone who is stressed and has a poor diet. Remember, too, that the appearance of a plant can be deceiving--sometimes a plant may look lush and healthy to a human eye, when in reality it is stressed due to excessive water, fertilizer, or shade. The kinds of healthy, naturally fertilized plantings in a stacked agroforestry system, providing appropriate niches and microclimates for many species, is helpful in contributing to plant health.
These are some tips for fostering a system with healthy plants:
- Select plants that are well adapted to your site
- Select plants that genetically retain natural defenses, and are not overly bred by people
- Fertilize through use of added organic matter, not soluble fertilizers or large amounts of uncomposted manure
Diversity of plant species can go a long way in reducing susceptibility of plantings to insect pest problems. Monocultures concentrate the food source of the pest species, and hence give rise to high populations of that pest. By using a patchwork of species, there is reduced concentration of food source for pests, and some pests may not be able to readily identify their food source in the mixture. A mixture of species also provides diverse habitat for pest predators. A balance of pests and predators is a key to natural pest management. Predators include other insects, as well as spiders, birds, frogs, reptiles, and other predators. There are some specific elements you can add to your planting that will help attract predators such as ponds or water sources (to attract frogs, birds, and reptiles); trees which provide habitat, and certain flowering plants (to attract predatory wasps, etc.). It should also be noted that in diverse plantings, if a serious pest problem arises, there are diversified crops to support the economic survival of the farm or forest.
Tips for diversity:
- Use a diversity of species which fill interchangeable roles in windbreaks, shade, commercial crops, etc.
- Use plant materials for each species with diverse genetic make-up--avoid excessive use grafted/cloned plants.
- Use modern selections as well as heirloom varieties
- Use native and exotic species
- Limit contiguous plantings of a single species through the use of patchwork plantings
Fukuoka, Mansanobu. 1978. The One Straw Revolution, Rodale Press. Documents pest management based on observation of nature. This title is out-of-print, but is very much worth looking for in used bookstores.
ECHO's comprehensive Amaranth to Zai Holes: Ideas for Growing Food Under Difficult Conditions sites excellent biocontrol resources.
About the Authors
Kim M. Wilkinson is the Education Director for Permanent Agriculture Resources and editor of The Overstory. She has B.A. degrees in Anthropology and Ecology from Emory University.
Craig R. Elevitch is an agroforestry specialist with more than ten years of public and private sector experience in tropical agroforest and forest management. He has a M.S. degree in Electrical Engineering (Dynamical Systems) from Cornell University.
Related Editions to The Overstory
- The Overstory #61--Effects of Trees on Soils
- The Overstory #21--Agroforestry and Biological Diversity
- The Overstory #14--Getting Started: Diversity of Species
- The Overstory #8--Mycorrhizae