By Chuck Schembre
Orchard crops may receive the most pesticide and chemical applications of all crops. Some varieties will receive 20 or more pesticide applications per year. This has become one of the main tasks for an orchardist: sitting in a tractor and spraying.
One of the most powerful arguments for regenerative agriculture is thus the potential to greatly reduce or eliminate toxic pesticide applications.
After decades of proven examples in many crops in many climates, it is undeniable that regenerative farming methods — agroecological farming — can lead to farms and crops that are completely free of disease. What these farms all have in common is healthy soil, abundant farm biodiversity, and optimal plant nutrition, supported by the soil and plant microbiome.
My farming career began more than 20 years ago on small, highly diversified, bio-intensive, organic farms, with an emphasis on agroecology. On those mixed vegetables and small polyculture orchards, disease and pests did not cause catastrophic crop damage. Using external inputs to control outbreaks was not in my farming paradigm. At the time I took this privilege for granted. I did not completely understand the mechanisms at play leading to crop and farm resiliency — I just trusted the process of a non-conventional chemical approach, focused on natural farming techniques, producing nutritious food for the community.
Over the years, though, I have farmed and consulted on many large farms with less diversity and have witnessed incredible disease and pest pressure, both on organic and conventional farms. I have spent a lot of time obsessing over organic and biological controls and have learned from many pioneering experts — and from the lessons of hard knock on the fields. I’ve learned that there is no silver bullet — there are many ways to skin the cat to achieve natural resistance against disease, and control over pests.
What needs to be well understood, and embraced, is a multi-pronged, adaptive approach rooted in a foundation of healthy soils and farm-ecosystem function. Let’s begin by remembering the fundamental reasons disease and pests often prevail.The Root Cause of Disease
The are certainly many factors at play as to why a disease or pest becomes extreme or prevalent in a specific crop and region. Naturally, there is more potential for fungal disease in humid climates, or adaptation and mutation of a pathogen over time due to fungicide resistant and monocrop farming. But in all circumstances where disease and pests are abundant, the major issue is soil dysfunction, or poor soil health — i.e., soil that is devoid of a healthy microbiome.
This underground problem is expressed aboveground: dysfunction exists in farms that lack biodiversity, where ecosystem processes are broken. The crops generally have poor nutritional health and a weakened immune system, only surviving on chemical life-support, achieving merely the yields required to offset farming costs.
I can’t emphasize this next point enough: if you want to build true disease and pest resistance in your field, you must start with a foundation of intentionally farming by the principles of soil health. This requires being brutally honest about the current condition of your soil health and being willing to recognize the core management decisions that are causing excessive soil disturbance — whether from chemicals or from equipment.
Disease-Suppressive Soils
A disease-suppressive soil is pretty simple by my definition: It is a soil that is well aggregated, down to at least 12 inches for most soil types, with abundant pore space that allows for optimal gas flow and exchange, water infiltration, and water retention. A well-aggregated soil has the ability to cycle gases, water and nutrients. It abounds in diverse soil microbes, which support much of the plant’s nutritional requirements while regulating and balancing the soil ecosystem.
A disease-suppressive soil — i.e., a well-aggregated soil — will exhibit both anerobic and aerobic conditions, or pockets, down to the micro-aggregate level. In my experience, if soils are not well aggregated down to at least six inches, its biological nutrient cycling and disease-suppressive properties will be poor. Well-aggregated soils also reflect the abundance of saprophytic fungi on the soil surface, which play a critical role in pathogen regulation.
The Profound Role of Fungi in Perennial Crops
I have unfortunately found that most operators of large orchards and vineyards are not well educated in regard to the life support and plant immunity role of fungi for perennial crops.
All orchard crops — whether fruit trees, nut crops, grapes or berries — have a strong symbiotic relationship with fungal life, both in the soil and in the plant canopy (the phyllosphere). Without an abundance of fungi, perennial crops cannot develop a strong immune system or natural defense mechanisms against disease and pests. The physiology of trees — including photosynthesis, the uptake of nutrients, the synthesis of proteins and carbohydrates, and the ability to resist disease and pests — relies heavily upon mycorrhizal and saprophytic fungi, among many other soil microbial species. Soil microorganisms, specifically mycorrhizal fungi, are key players in the availability and transport of micronutrients to the tree. Micronutrients, or trace elements, are critical in the function of plant disease protection. Research has also found that mycorrhizal fungi have a supporting role in the populations of nutrient-solubilizing bacteria, which support the availability of many macro- and micronutrients. Without a robust population of mycorrhizal fungi in the orchard, trees exist in a state of poor health.
Saprophytic fungi may be of equal importance to tree and vine health, and are often less talked about. This family of fungi are the primary decomposers of dead organic matter, such as residues, leaves, woody material, and other dead organisms. They are responsible for breaking down lignin and cellulose, turning organic matter into carbon sources that the lower trophic soil level can feed on, and for unlocking further nutrients for the plant.
But the most powerful thing about saprophytic fungi is their role in pathogen regulation, both in the soil and in the plant canopy. Many of the common orchard fungal pathogens that cause huge economic stress are saprophytic by nature. In nature, or in a healthy soil ecosystem, pathogen outbreak is kept in check and regulated by other saprophytic species.
Ecological research has revealed an abundance of saprophytic fungi and bacteria in and on the bark and leaves of a tree’s canopy. The microbiome of the tree canopy, including the trunk, is known as the phllyosphere. The organisms in the tree regulate and suppress disease pathogens. They also help solubilize atmospheric nutrients and support the function of stomata and moisture regulation.
If there is immense pressure from an insect or fungal pathogen, there is a deep imbalance within the farm ecosystem. This is often a problem that no product can solve. When conventional (and many certified organic) fungicides are applied, the tree microbiome is greatly disturbed. Systemic fungicides have a lasting effect on the ecosystem, regulating the regrowth of many fungi for two to three weeks. Conventional fungicide chemistries are great at what they were designed to do — wiping out saprophytic fungi, including the good guys. Spray mist also settles to the soil surface, killing more fungi and bacteria.
So, what can we do about this? We can’t just stop spraying, naively wishing that the good guys will control the bad guys, right? The transition can be a challenge.
Measuring Soil Biology
Most conventional orchards and vineyards that bring me in to consult have very little soil fungi, as measured in the soil Phospholipid Fatty Acid tests (PLFA). These tests give me a ballpark understanding of the soil’s biological health and diversity, and potential biological support, both from a nutrient cycling and disease-suppression perspective. As I see fungi levels building in the PLFA tests I can become confident in reducing and eliminating conventional fungicides.
I have found that a total fungal biomass of 500 ng/g on the PLFA is a good benchmark for a healthy level of fungi for most soils. I have seen it much higher, and I believe that values of 1,000 ng/g indicate a strong state of soil health. In the regenerative transition, once the fungal numbers are high, we can begin controlling disease, while greatly reducing or eliminating pesticides, by optimizing complete nutrition.
In part two of this series, I’ll examine the nuts and bolts of the systemic implementation of the principles and practices that empower regenerative strategies for orchard disease and pest control.