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Grey Mold on fruit, bud rot

Natural Fungicide for Plants

Plant pathogens cause disease and damage in plants. Whether you’re looking to manage plant health in your garden at home, or you are a professional grower, it’s important to understand the basics of fighting plant pathogens and diseases using pesticides. Some people shy away from pesticides because of the bad name that they’ve gotten over the years. They associate them with synthetic chemicals that harm the environment, and sometimes people. But that’s where natural products come in. Natural fungicide for plants can be a great option to maintain plant health and comply with organic growing standards.

The truth is, pesticides are not inherently bad. They are a necessary part of pest management, and can be very safe when applied properly. Not all pesticides are made from synthetic chemicals either. There are many natural and organic certified products out on the market that help maintain the health of your crops. In this article we’ll focus on everything you need to know about natural fungicide for plants. 

Natural Fungicide for plants could do wonders here
You can see the white spots covering the leaves is powdery mildew, and this squash could really use a natural fungicide for plants to control the problem while keeping the fruit edible.

What Are Fungicides?

A fungicide is a type of pesticide. Pesticides are usually broken down into three main categories based on what they target: fungicides, herbicides, and insecticides. Fungicides attack a fungus, a type of plant pathogen, or multiple different fungi that cause fungal infections of your plants. Fungi are the leading cause of crop loss around the world.

Herbicides on the other hand are used to control unwanted vegetation, like weeds, and insecticides combat damage from insects. Curious about insecticides? Check out our article on the best insecticide for your vegetable garden.

Diagnose the Problem Before Picking a Pesticide

On top of the three main categories, other organisms can also cause disease in your plants. Viruses, bacteria, and nematodes are other common plant pathogens. Because different pesticides target different problems, it’s important to diagnose the root cause of the symptoms before you apply a product to your plants. One type of pesticide will not fight all pests, so you want to make sure that the one you choose will target the right disease by killing or inhibiting the plant pathogen that is causing it.

Why Do I Need to Apply Fungicides?

If you’re a grower, you know that disease management is an important part of the process. Plant diseases are common and can have a real effect on your productivity and profitability.

Fungal diseases can cause damage to the leaves of your plants, which affects photosynthesis, and therefore the growth and production of your plants. And once the damage is done, there isn’t much you can do to reverse it. Because the plant is weakened, diseases can also manifest in lower yield and quality of your harvest.

Preventive Plant Health

Fungicides are like a Tetanus shot. You get an initial vaccine to prevent the infection, and then you continue to get periodic boosters to maintain that defense. You don’t expect to step on a rusty nail tomorrow, but the shot is your insurance policy in case you do. It gives you a better chance at avoiding serious damage and preventing the disease in case you’re exposed to the pathogen.

Fungicides are the same way. Most are preventive measures, to protect your crops from fungal diseases. They are most effective when applied before any symptoms of the disease are visible, or immediately after. Even though the pathogen may be killed by the fungicide, it can’t reverse the symptoms that already exist. Established plant pathogens that have already gotten a hold of your plants don’t generally respond to any pesticides, so it’s important to have that layer of defense before the disease progresses.

How Do Fungicides Work?

Application and Frequency

Fungicides are typically applied to plants as a liquid spray. Less common forms of fungicides are granules, dust, and gas. If you’re growing in a greenhouse, you might also consider applying fungicides as a mist or fog.

Most fungicides need to be applied to the plants regularly. This will help protect any new growth in your crop, and combat product loss to the environment from irrigation or rain. Depending on the product and disease, you may need to continue applying the fungicide every 7, 10, or 14 days throughout the growing season.

Many growers try to predict the optimal time to apply fungicides based on temperature and humidity, when the pathogen will be most active. But when it comes down to it, it’s all about the money. It’s an added expense to your growing operation to be continually spraying your plants with fungicides, but the risk you take in not protecting them could be even more costly.

a natural fungicide for plants will get rid of this problem
Another case of powdery mildew that is destroying plant leaves. You can see the leaf on the right is permanently damaged from the fungus.

Contacts vs. Systemics

Fungicides are generally categorized as either contacts or systemics. Contact fungicides, also known as protectants, do not move past the surface of the plant where they are applied. These types of fungicides remain on the outside of the plant, on its leaves and stem, until they are washed away or broken down chemically, for example by UV rays from the sun. Systemics, or penetrants as they’re sometimes called, can be absorbed by the plant and travel small distances.

Either way, most fungicides don’t move well through the plant, or they remain completely on its exterior, so the application area is very important. You want to try to cover all parts of the plant that might be prone to the pathogen or disease. This includes the back side of leaves as well.

Range of Activity

Single-site activity in a fungicide means that it is targeting a pathogen in a specific way. The product might disrupt a necessary metabolic pathway, inhibiting the growth of a fungus, or be formulated precisely to attack and kill it by destroying the cell membrane. Because of how specific these types of fungicides are, they are less likely to be toxic to the plant, and more likely to have systemic mobility, penetrating into the plant. They can also be prone to resistance, as the pathogens mutate and adapt to the specific mode of action.

Multi-site activity casts a wider net, so it can affect many different fungi. These fungicides tend to be contact products, remaining on the surface of the plant.

It’s important to know the mode of action and whether the fungicide has single-site or multi-site activity, to determine what plant pathogens it can be used for. Another way to describe this is narrow-spectrum vs. broad-spectrum fungicides. A narrow-spectrum product is only effective at controlling a few pathogens, while a broad-spectrum is able to prevent many different types of fungi.

What Are Common Plant Diseases Caused by Fungi?

Below is a list of the most common fungal diseases that cause damage to plants. It’s always a good idea to get samples tested by a certified lab if you’re not sure of the diagnosis, before applying any fungicides for treatment.

  • Powdery Mildew: leaves have a white, powdery growth
  • Black Spot: leaves develop dark spots on top surrounded by yellow
  • Rust: rust colored growth develops on the underside of leaves
  • Botrytis Blight: grey, fuzzy mold grows on decaying flower petals and buds

Fungal diseases often exhibit with symptoms that are visible on the leaves of the plant. You might also see clear signs of fungal growth. Fungal activity and plant diseases are typically promoted by wet conditions with poor air circulation.

What Are Fungicides Made From?

Synthetic Fungicide

There have been many different active ingredients in commercial fungicides over the years. One of the most common today, triazoles, were first developed in the 1970s. Although they are organic from a chemical compound point of view (they contain carbon), they are derived from chemical synthesis, not occurring naturally in the environment. Synthetic fungicides have active ingredients that have been created in the lab.

Even though there are many safe synthetic compounds that are used in fungicides, there are also a number that have been banned as our collective knowledge has grown throughout the last century.

Natural Fungicide

Fungicides formulated using natural products are usually considered to be more environmentally friendly. They provide effective protection for your plants, but with minimal impact on the environment. Common active ingredients in natural fungicides include:

  • Sulfur
  • Copper
  • Horticultural and Neem Oils
  • Bicarbonates

Many of these natural compounds have been used as fungicides for hundreds or even thousands of years. In fact, before commercial fungicides were available, many growers would make their own fungicides by mixing ingredients according to simple recipes.

Sulfur is probably the oldest natural fungicide. It prevents fungal spores from growing, and can help control rusts, black spot, and powdery mildew if applied early enough, before the disease progresses. However, there are certain plants, like raspberries, that should not be treated with sulfur, and applying it in hot climates can cause damage to plants.

Copper is often found in natural fungicides. Rather than inhibiting growth, it kills both fungi and bacteria. But again, copper can be phytotoxic, damaging your plants, so the formulation is very important to mitigate any negative impact. Always use the proper dilution recommended on the label.

Horticultural oil and neem oil are mostly used to control insect damage to your garden, but also protect against powdery mildew and some viral plant diseases. Some species of trees are known to be sensitive to oils, and high temperatures and humidity increase the phytotoxicity of horticultural oils.

Bicarbonates, like baking soda, have also been used as natural fungicides for a long time. Ammonium bicarbonate and potassium bicarbonate are recommended over baking soda because they are effective without the additional use of oils, and they offer added nutrients to plants (nitrogen and potassium). The sodium in baking soda (sodium bicarbonate) can accumulate and become toxic to your plants.

Organic Materials Review Institute

Not all natural products are certified organic. The Organic Materials Review Institute, OMRI, is a third party reviewer of products to help growers know which ones they can reliably use in certified organic farming operations. Their goal is to support organic integrity. If you see a product that is OMRI listed, you know that it has gone through a thorough review against organic standards, making it a top tier natural product.

Are You Looking for a Natural Fungicide for Powdery Mildew in Your Garden?

If so, then we’ve got the right product for you. Grower’s Ally is a family of products that is OMRI listed for use in organic gardening. Their two products, a fungicide and an insecticide, target powdery mildew, spider mites, and russet mites. They are all natural, so the Grower’s Ally products have no synthetic pesticides, no heavy metals, and no residual solvents in them.

One of the Best Fungicides on the Market

Grower’s Ally Fungicide has been proven to control common plant pathogens, including powdery mildew. Not only does it combat fungi, but it is a bactericide, fighting bacterial plant diseases as well.

This certified organic fungicide has a non-systemic, or contact mobility, so it remains on the surface of your plants. It forms a protective barrier, and controls fungal growth by dehydrating the fungi and preventing new spores from growing.


It is one of the best options for natural fungicides, not just because it tests clean and is safe for bees, but because it has no known phytotoxicity. That means there have been no reports of any plants that have had adverse effects from this fungicide. Which is a limitation for some of the natural active ingredients that we discussed above.

Grower’s Ally Fungicide is formulated with food-grade citric acid. It can be safely applied at any stage of plant growth, and without any PPE because it is non-toxic. It can be used in various growing environments, including indoor, outdoor, greenhouse, and hydroponic.


This fungicide should be sprayed every 5-10 days depending on the case, whether there are already symptoms of disease or it is being used as a preventive measure. For proper application, spraying should cover all stems and leaves, including the undersides.


Fungicides are a critical part of a robust pest control plan for your garden or growing operation. They’re used primarily as preventive measures to protect plants from pathogens and maintain plant health. Although there are viable synthetic fungicides on the market, natural fungicides for plants offer lesser environmental impact, and are more compatible with organic farming practices. If you’re struggling with fungal diseases, make sure to properly diagnose the cause, and then consider a natural fungicide, like Grower’s Ally.

By Alli Klein

Alli is a copywriter with a passion for sharing knowledge. She has her Bachelor’s degree in Chemical Engineering from UCLA and contributes articles as a hobby outside of her day job. She loves being outdoors, spending time with her dogs, and is working on cultivating her own garden in Idaho.

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