Integrated Pest Management: Building on the Basics
This month, I'd like to continue building on the basics of integrated pest management. If you recall, there are five main components to a successful IPM program1:
- Pest identification
- Field monitoring and population assessment
- Control action guidelines
- Preventing pest problems
- Integrating biological, chemical, cultural, and physical/mechanical management tools
Preventing Pest Problems
A large percentage of pest problems can be traced back to issues with cultural practices—that is, meeting basic plant needs through good water management, healthy soil, proper nutrients, and appropriate site and plant selection. A pathogen (a microorganism that causes disease) can only cause disease when three elements are present: a susceptible host, the pathogen itself, and a favorable environment. This relationship can be visualized in the disease triangle, with each element represented by a side of the triangle.
Preventive practices eliminate one or more of the elements of the disease triangle. The care you take as the manager of your landscape can improve your plant's ability to protect itself, giving it the best chance of enduring the things we can't prevent—like pathogens, pests, drought, weather extremes, and other stressors. Preventive practices can also make it more difficult for pests and pathogens to thrive. This will reduce the need for pesticides and other management strategies.
Starting with Soil
Plants are autotrophs, which means they can produce their own energy through photosynthesis. However, they rely heavily on the soil for elements crucial to their survival, like water, stability, and nutrients. Because the soil is so vital to plant health, caring for the soil must be central to any IPM program.
Soil Composition
Oxford languages defines soil as “the upper layer of earth in which plants grow.” It is made up of inorganic minerals, organic matter, soil organisms and microorganisms, gases, and water. From a physical standpoint, there are a few key soil terms and concepts you should understand. Let's go through them quickly
Soil inorganic minerals come from the weathering of rock, and are grouped by size; soil texture refers to the percentage of these groups—sand, silt, and clay—in a soil and is represented in the soil textural triangle below. Loam refers to a mix of these three groups. Soil texture largely determines a soil's nutrient- and water-holding capacity. Plant roots need both water and air, so good soil should have a balance of drainage and water-holding capacity. Soil with ideal moisture content will have 25% air and 25% water. Because of its larger particles, sandy soil tends to drain well, but doesn't hold water or nutrients well. On the other hand, finer-textured soils (clay and silt) hold more water and nutrients, but often don't drain well. However, adding soil organic matter to sandy soil will help it hold water, and adding it to fine-textured soils will help it hold nutrients.
Soil organic matter (SOM) is any soil material produced originally by living organisms that is returned to the soil and decomposed. This includes the soil organisms themselves (bacteria, fungi, plants, insects, animals, etc.), plus their waste and other byproducts. SOM is vital to soil function in many ways, so I'll go into more detail about it later.
Soil Structure
Soil structure refers to how soil particles and organic matter are arranged into aggregates, or groups of bound particles. Aggregate stability is the ability of aggregates to withstand breakdown by outside forces, like water. It's important for preventing erosion. Pores are the spaces between and within aggregates that allow movement of water and air into the soil—and the growth of plant roots! Adding organic matter to both sandy and fine (silt and clay) soil will encourage soil aggregation.
Compaction happens when soil aggregates and pores are broken down through activities like heavy traffic and tillage. It impedes root growth and the movement of air and water in the soil. Bulk density is an indicator of soil compaction calculated as the dry weight of soil divided by its volume.
Soil Nutrients
The 15 essential soil nutrients are the more well-known elements of soil. The macronutrients are needed in larger amounts by plants, and consist of: 1) primary nutrients nitrogen (N), phosphorus (P), and potassium (K), which are most often deficient in soils, and 2) secondary nutrients calcium (Ca), magnesium (Mg), and sulfur (S), which tend to be deficient in soils less often. The nine remaining nutrients are micronutrients, which the plant requires in very small quantities. These are boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn). In California, the most common deficiencies are nitrogen, phosphorus, potassium, zinc, and iron. Boron, chloride, and sodium, on the other hand, are more commonly present at toxic levels.
Soil pH
Another important physical component of soil is pH. pH is a measure of how acidic or basic soil is. It ranges from 0 to 14: 0 is most acidic, 14 is most basic, and 7 is neutral. Most crops prefer a slightly acidic to neutral pH of 5.5 to 7.5. Acidity is a measurement of how many hydrogen ions are in the soil, and pH can impact soil chemistry in numerous ways. pH extremes may increase the solubility of toxic mineral elements like aluminum and manganese, or increase the concentration of soluble salts, all of which are detrimental to the plant. pH also impacts which organisms can survive in the soil, which will also impact your plant. Of chief concern to the landscape manager is that plant nutrients become insoluble in water, and unavailable to plants, if the pH is too low or too high. The table below illustrates this fact.
Soil Quality vs. Soil Health
If the information I've presented here feels overwhelming, don't worry. Many have shared your experience, including me. If you've made it this far, though, you've shown admirable perseverance and curiosity. And this information isn't going anywhere. Bookmark this page and come back to it periodically; it will start to make more sense over time. Understanding the physical attributes of soil, or soil quality, is not only important in its own right, but it's also foundational to what I'd call the more exciting stuff—soil health.
Soil health moves beyond the physical attributes of soil to include the whole soil ecosystem—all the life in the soil, great and small—not just plants. It is “the capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health”[i]. Soil health is critical not only to integrated pest management, but also to human health and the health of our planet. So check out my next blog to hear more!
Author info:
Gretchen Heimlich-Villalta is an ISA™ certified arborist who has been a San Bernardino County Master Gardener since 2014. She received her AS in Integrated Pest Management from Mt. San Antonio College, where she has helped teach IPM since 2020. She received BA degrees in Creative Writing and Photography, and is currently working on her Ph.D. in Plant Pathology at the University of California, Riverside, where she is researching citrus root and soil health; she also helps manage the Strub Avenue Community Garden in Whittier.
[i] Doran and Zeiss, 2000.
