Behind The Spray: What Research Says About Homemade And Natural Fungicides
 | Author:
Allison Kosto, MSU Broadwater County Extension Agent
MSU Broadwater County Extension Agent |
Behind the Spray: What Research Says About Homemade and Natural Fungicides
Allison Kosto
MSU Broadwater County Extension Agent
Inevitably, I get questions every summer about homemade pesticides. I’ve done articles in the past about herbicides and insecticides, but also wanted to address fungicides, which are used to battle plant diseases.
A disease is a condition that affects a plant’s growth and function, such as a fungus, bacteria, virus or environmental cause. It doesn’t take long through a quick internet search to find a slew of homemade recipes to combat diseases, and it’s easy to see the allure of homemade and natural pesticides. They often seem less expensive, and many people believe they are safer. However, homemade and natural pesticides are not as simple as they sound. It’s important to analyze the safety and effectiveness of these substances before using them around your home or yard.
The most common ingredient in homemade fungicides is baking soda. In fact, it has been used as a fungicide since 1933. It is most commonly used against powdery mildew. It works by creating an alkaline environment on the leaf surface to prevent or slow the growth of fungal spores. It does not actually kill the fungus. Therefore, it is only effective as a preventative fungicide. Research has shown that baking soda alone results in inconsistent outcomes, so it is often best to use it in conjunction with other products. Additionally, because it is water-soluble, it needs to be reapplied frequently. A major concern about baking soda is that it has a high sodium content. Repeated and long-term use of baking soda can raise the sodium levels in the soil, which can negatively impact plant growth.
Sulfur and copper are two organic fungicides that also have a long history of use. It is highly recommended to purchase commercial products for safety reasons. Commercial products labeled as a pesticide must be registered with the EPA or have an official exemption. These products undergo rigorous testing which looks at many factors including, but not limited to, environmental impact, food residues and safety. Testing also determines how much product to use, where to use it and when to use it. Products are labeled according to the EPA specifications to ensure that they are safe when used properly based on label instructions.
Records show the use of sulfur as a fungicide started over 2,000 years ago when the Greeks used it against wheat rust diseases. It can also be used against powdery mildew, rose black spot and others. Just like most fungicides, it is preventative, so must be applied before the fungus develops. Even with natural products, there are limitations. Some fruits such as gooseberries, raspberries, cucumbers and melons are sensitive to sulfur, and it should not be used on them. When combined with other products such as oils, sulfur can also become phytotoxic.
Copper can be used to kill fungi and bacteria. However, it should be used with caution to avoid plant damage and should not be used over extended periods of time because copper will start to build up in the soil, resulting in negative effects.
Managing diseases can often be successfully done without pesticides by managing the ‘disease triangle.’ In order for a disease to occur, there must be three active factors (cornerstones of the triangle): the plant host, the pathogen and the favorable environment. If you can figure out how to remove one of the factors, then you can successfully control the disease. For example, powdery mildew may be controlled by altering environmental conditions, so the disease is less prevalent. Ways to do this are increasing row or plant spacing, improving air circulation and avoiding overhead watering. Another example in the case of fire blight is to focus on the plant host. Some varieties of apples are naturally resistant to fire blight, so by planting these varieties, you can reduce the prevalence of fire blight.
It’s also important to note that the effectiveness of homemade pesticides is highly variable. Because there are no standard recipes or application instructions and they are not tested, results will vary. Even though it may seem more economical to make a homemade product, the reality is that it is less risky to purchase the convenient and reliable commercial product. There are many organic and natural commercial products available.
If you want to use a homemade or natural product, do your research to understand the science behind the chemicals and the implications of using the pesticide. Test the product on a small part of the plant leaf prior to spraying a large area. When using pesticides, ALWAYS follow label instructions.
One of the wonderful things about a home garden is that you have the ability to control the management practices for your own fruits and vegetables. You have the ability to choose organic, natural or conventional techniques or a combination. I don’t advocate for one or the other. Instead, as part of MSU Extension, my goal is to provide you with unbiased research-based information so that you can make an informed decision about how you would like to manage your garden. If you have questions about pest identification or control, contact MSU Extension Office in Broadwater County at 406-266-9242 or allison.kosto@montana.edu
