At the first sign of insects or disease in our vegetable gardens, we have been trained to pull out the chemical sprays to resolve the problem quickly, without giving much consideration to the damage we may be doing in the long run. While we do know that synthetic pesticides will kill disease and insects – are we truly aware of how they affect the rest of the garden ecosystem? Furthermore, because we are part of that ecosystem – have we considered how they can affect our own health?
Effects of Chemicals on the Plant Root Zone
Some fungi cause plant disease, such as powdery mildew or fusarium rot. Using a fungicide to control these diseases temporarily sets the pathogenic fungi back. But fungicides take care of the disease-causing organisms while also poisoning beneficial fungi. Most fungi are beneficial to plant health.
In the plant root zone, the rhizosphere, mycorrhizal fungi create symbiotic relationships with plant roots. Over 90% of plant species have, over eons, evolved these beneficial relationships. Fungi develop long strands of cells strung together, called hyphae, that extend far beyond the plant root zone. The hyphae deliver nutrients and water back to the plant and in exchange the plant gives sugars to the fungi. A strong fungal relationship is one aspect of a diverse soil biology that protects plants from insects and disease. A diversity of beneficial soil biology leaves little space for pathogens to create issues.
When fungicides are used to control fungal diseases, the beneficial fungi in the root zone are also affected. Studies show when fungicides are used there is a marked decrease in mycorrhizal fungi. (1) That decrease indirectly affects the entire soil biota and the availability of nutrients to plants. Even when a foliar spray of fungicide is used, soil fungi will still decrease. For a foliar fungicide to be effective it must be sprayed until it drips, which means it will inevitably impact the soil biology.
Pesticide Use and Soil Biodiversity
Fungicides may not kill bacteria, but they do create a less hospitable environment because they cause a decrease in soil biodiversity. The term “pesticide” is used more generically to include chemicals that kill insect pests as well as fungal and bacterial pathogens. When any part of a well-functioning soil food web is disturbed, it affects the entire soil community.
Our bodies are subject to the same types of microbial activity, although with different species than those found in soil. Humans have evolved numerous methods to slow pathogen entry into our bodies. Mucous membranes secrete antimicrobial fluids, our skin is a barrier unless punctured, and the microbiome in our gut detects and removes pathogens. These all work well to ward off disease unless our body or immune system is somehow compromised. (2)
One way our body can be weakened is by using an antibiotic to speed the healing process. There are many reasons to use antibiotics, but there are many situations when they may not do any good. Frequent use can lead to antibiotic-resistant pathogenic microbes.
In our body, an antibiotic such as Penicillin may take care of an infection, but it would also potentially destroy many beneficial microorganisms, especially in our gut microbiome. In many ways antibiotics are the same as pesticides. They take out both disease-causing microorganisms and weaken or destroy beneficial microbes.
Penicillin is an antibiotic that has been synthesized from the natural fungal penicillium. In soil, billions of microorganisms are jockeying for nutrients and especially for a place on plant root cells. Fungi have developed chemical defenses against pathogenic fungi and bacteria. Bacteria and viruses in the soil are constantly at war. Bacteria have developed ways to restrict virus infection and to capture a part of the virus, which keeps it from completing its life cycle. (3)
In healthy soil with lots of organic matter there are billions of beneficial and pathogenic microorganisms. Spraying a pesticide disrupts the balance, kills or weakens beneficial microbes, and gives pathogens an opportunity to gain nutrients. With an imbalance the odds are in favor of increased pathogens because pesticide resistance is becoming common.
When disease appears again, more spraying is done, more beneficial microorganisms die, more room is created for pathogens. Chemical use as a control of disease and pests can ultimately create more problems, which nature can solve if we have just a bit of patience.
Patience Creates a Positive Domino Effect in the Garden
If you happen to see a few aphids on your rose bush, you have a few options to control them. You may be tempted at first to use a chemical spray, but you may be creating more problems than you would potentially solve. What you may need is simply patience combined with some close observation.
This requires taking a holistic view of your garden and the ecosystem surrounding it. It involves waiting and watching to see which predatory insects first find those aphids. Will it be ladybugs, lacewings, or parasitic wasps? Aphids and most soft bodied insects have numerous predators. Creating the proper habitat for biological control of aphids will make gardening so much more pleasant and productive.
Beneficial insect habitat will vary depending on where you are located. Insects evolve with the native plants that give them pollen, nectar, and a place to lay their eggs. Planting some native plants in your flower beds and around the edges of your vegetable garden will allow these beneficial bugs to be close by, so they can snag those aphids and other pests like tomato hornworms (or their eggs). There are very good reasons to plant many different plant species together. Some of them will attract beneficials, some will repel pests, and all of them will increase soil biodiversity, which is the ultimate goal.
Creating Symbiotic Relationships in Your Vegetable Garden
If you can learn to accept a few weeds and a bit of insect damage, your reward will be an expanse of garden biodiversity both above and below ground. Many insects spend a part of their lives in the soil. They add to the biodiversity of fungi, bacteria, nematodes, earthworms, and many other soil organisms.
Those soil organisms need organic matter and break it down for nutrients. Bacteria and fungi are superior decomposers of organic matter. They are prey for larger soil biology such as nematodes and protozoa. Bacteria need more nutrients than their predators. When a protozoan, for example, consumes a bacterium it releases nutrients it doesn’t need into the plant root zone. Those nutrients are then taken up by plants.
Mulching with leaves, straw, compost, and other organic materials keeps weeds down and feeds your soil biology. Wood chips also keep down weeds and are a valuable source of soil nutrients. Wood chips are coarser than compost or most other organic materials. If you lift up a bit of wood chip mulch you will find long white threads. Those are fungal mycelium, bunches of fungal hyphae grouped together. They are decomposing that wood, depositing carbon in the soil, and creating an environment hospitable to a diversity of soil biology.
But not all wood chips or mulch are created equal. Clippings from the deciduous shrubs and trees you’ve just pruned are the best for your garden. They’re referred to as ramial wood chips and when they’re chopped up a bit are a feast for soil biology. (4) They’re softer than larger diameter pieces of wood and decompose faster.
When buying wood chips or mulch remember they are a food source for your soil biology. Just like you don’t want a bunch of additives in your food, neither does your soil biology. Wood chips need to be untreated and undyed. Hardwood and softwood mulches come in different particle sizes, the smaller the particles the faster they decompose.
Hint: If mulch made from any organic material isn’t decomposing that’s a sign you don’t have a healthy soil microbiome. Take a look at your gardening practices. Are you using a lot of pesticides or fertilizers? Mulch is an effective pesticide by creating a hospitable environment for beneficial insects. It also acts as a slow-release natural fertilizer, releasing nutrients to the soil and your plants through the actions of soil biology.
The only wood that doesn’t benefit your soil biology is cedar. It’s both antimicrobial and antifungal. And for those reasons it lasts a long time as mulch but repels beneficial insects and soil biology. Not exactly the best choice to improve your garden soil.
Natural Solutions to Plant Problems in Your Garden
The first line of defense in avoiding plant problems is to work with nature. Soil contains billions of living organisms which protect plants from disease and pathogens. Those organisms create a complete soil food web which expands to include frogs, toads, birds, and other vertebrates – including humans. Plants also play an active role in creating biodiversity.
Next time you’re in the garden and see an insect, take a picture. Wait a few days and see which predator takes care of it. Identify the insect; it might be one of the predators or predator larvae. Aren’t you glad you didn’t kill it?
Integrated Pest Management (IPM) is allowing beneficial insects to help you control pests in the garden. Leave the spider and its web, you’ll see how beneficial it is by how many insects are caught in the web.
A riot of aboveground diversity in your garden creates a diversity of soil biology. One way to create that diversity is through companion planting. You’ll enjoy a greater diversity of foods and feed a more diverse soil biology. Look at your garden as part of a larger ecosystem. That lets you see how lawn fertilizer may affect your garden and how mulching your garden benefits your lawn.
If you’re growing in raised beds make sure the soil you’re adding is high quality. Mix in good compost or water with compost tea. Mulching a raised bed will help retain moisture and keep the soil cool.
Watering in a natural soil amendment, such as Kaytonik, allows you to feed your soil biology safely. There are no chemicals and it’s safe for children and pets. Your crops will benefit from the enhanced soil biology and you’ll eat nutrient dense food.
The adage “you are what you eat” is true. Looking at the larger ecosystem that adage includes the entire soil food web. That healthy ecosystem includes a healthy you.
- Phillips, Michael, The Holistic Orchard, Chelsea Green Publishing, 2011. Pg 7-8