The Best Fungicides for Getting Rid of Powdery Mildew, Snow Mold, Grass and Lawn Fungi

Today tons of fungicides aimed at eliminating harmful plant fungus and at protecting them from terrible diseases are sold in stores all over the place.

Too many factors influence the choice of a right fungicide, such as the species and the age of a plant, the type of disease and how far it’s progressed. The weather, the area covered by the green plants and pets nearby matter as well. All in all, getting confused is a piece of cake.

We don’t recommend buying a random fungicide as a well-marketed chemical can turn out to be a placebo. It can even harm a plant. The best thing to do is follow some professional advice.

Table of Contents:

Our guide unites the scientists’ recommendations and experienced farmers’ tips. We have intentionally placed the review of the most effective fungicide at the end of the review because it’s the diagnosis which comes first and foremost. In order to diagnose your plant correctly you need to know all there is about plant pests, and most of our guide is devoted to that matter! Getting rid of fungus takes wit!

Why is Fungus Dangerous for Plants?

All of the fungicides’ common enemies are pathogenic fungi which infect easily decorative and agricultural plants.  Farmers, housewives, food producers and gardeners all suffer from them.

Here's what fungal spores and fungi themselves are capable of:

  • They spoil the plants. Different diseases affect the color and shape of the fruit, leaves and flowers.
  • Fungi deprive us of the harvest. Within just a few weeks, they can damage potatoes, apples, grapes and wheat, tomatoes and cucumbers, blueberries and strawberries plantings.
  • They kill plants. Your lovely lawn or home plant can be easily destroyed if not treated with a fungicide in time.
  • Fungal diseases affect the farmers’ and state budgets. In some cases, the extent of crop losses from fungus becomes catastrophic and can lead to bankruptcy.

It is very difficult to avoid fungus infection without proper prevention. The spores are found in soil, air, other plants and water. They are spread with the wind, animals and even people! After that the mycelia which are very thin strings begin to act. They penetrate the plant tissue and begin to devour the living matter. In addition, the fungus-covered leaves do not get enough light and die without effecting photosynthesis.

Most Spread Plant Fungal Diseases

Most often it is the external symptoms which hint that the plant’s been infected with a fungus. Green plants can be covered with white scurf and rusty-hued pads, color spots and sores, and rotting pieces of lumpy outgrowths. Moreover, fungi make the plants wither, become deformed, dry, thinning, they get covered with tumors and cease to bear fruit.  In case of lawn and ground grass, fungi cause bald spots.

fungal diseases on trees

Any of these symptoms are caused by dozens of different types of fungi. This system is not easy to comprehend, but still the most common diseases have their scientific and common names.  Here are some of them.

  1. Powdery mildew. This versatile disease affects plant leaves, fruits, stems and flowers.  White scurf (which is mycelium) can fully weave around a garden rose or a vine within a couple of days. The disease kills fruits the longest as they rot and crack.  Young shoots are most prone to the powdery mildew. Pumpkins, peaches, gooseberry, grain, rose even sugar beets are akk the types of plants which suffer from it!
  2. Snow mold is the enemy of all natural lawns and tall grass fans. Snow mold usually appears in early spring after the snow has melted. It is spread in circles of a 3-12 inch diameter. When these circles thrive", the lawn can be irreversibly damaged.  First, it will be covered in pink, white or gray mold, then the fungus will pull out all the juice out of the grass, and it will die.  Most often fescue, perennial ryegrass and Kentucky bluegrass suffer from snow mold.
  3. Root rotting means such diseases as Rhizoctonia and "black rot" which are dangerous for most plants. Fungi erode the roots of home and garden plants. You will be oblivious for quite a long time as you’re just going to witness the plant gradually withering. This sinister disease turns the root system into the black dust or dry rusty lashes.
  4. Fungal leaf spots are a disease affecting vegetables. Some greasy dark spots are formed on the leaves. Most often tomatoes and peppers, potatoes, asparagus and rhubarb are affected by it.  University of Maryland scientists argue that this "beauty makeover" directly influences the productivity of vegetables while the fruits themselves are barely impacted.  
  5. And there exist also «Lawn fungus» and «Grass fungus». This is the popular name of a dozen diseases of decorative plants. It gets covered with rust-colored bubbles and red-brownish rings (Fusarium disease).  The lawn can become brown and disappear under small cotton clouds (Pythium disease).

Fungal Diseases Prevention

Fungi love humidity, stagnant weather and proximity to other plants. Therefore, it is crucial to maintain a certain interval between plantings, as well as to relieve them from excessive irrigation and poor air circulation. Bush J1 and Jander G on PublMed.gov  believe that these rules are particularly relevant for the greenhouse plants.  They advise regular monitoring of soil purity and disposing of dying crops.

The scientists Simeon Wright and Christopher Starbuck from UM recommend being careful with mulching and pruning plants (as a single error made during these procedures can lead to infection). They consider purchasing specially bred fungi-resistant species to be the best prevention.

According to Wright and Starbuck, sterile pots, soil mix control and smart irrigation eliminating stagnant water will protect the roots from fungus.

fungal diseases prevention

If you have already noticed some fungus on a tree or a bush, it’s crucial to remove it timely. Mary Bernand, a professional farmer, believes that when removing of the infected tissue it’s crucial avoid pruning branches and leaves, as any injury would become an "open gate" for new pests. It is better to gently break off the leaves, stalks and bark. She also advises avoiding top watering, which carries the spores and makes the leaves more vulnerable. It is better to pour directly under the root.

Mary Bernand is positive that the best organic prevention fungicide is the Bordeaux liquid, sulfur, copper, and fungicidal soap. She is sure that these, however, are not the most powerful tools which is why their application should be repeated regularly.

What Is the Difference between Various Fungicides?

Fungicides are classified depending on their application. Here’s what it looks like.

  1. Protective fungicides are organic and non-organic agent for preventing fungal diseases.
  2. Treatment fungicides are medications that can stop progression of the disease, and even destroy it.
  3. Systemic or complex fungicides are aimed both prevention and plant treatment.
  4. Immunizing agents improve the metabolism of the plants and make them resistant not only to the fungi but also to other bacterial diseases.

The operation of the chemicals also varies. For example, there are contact fungicides which are most often aimed at protection and which protect only the part of a plant on which they are applied. Disinfectants are popular with farmers and experienced gardeners. They treat seeds and bulbs with them so that they are not bothered by pests when grown.

Recently some organic liquid means, which move freely through the vascular system of plants, have become popular. They can save individual shoots of an infected plant or work as a protective and therapeutic agent.

What do all of the fungicides do to parasites? Some of them stop their growth and reproduction, others block enzymes and cellular respiration, and others do not let fungi synthesize proteins and lipids for cellular membranes.  Some of them pulled all the liquid (and consequently, life) out of a parasite.

Which is Better: Organic vs Non-organic Fungicides?

You have to first figure out whether you’re looking for an organic or non-organic fungicide. The former is considered more environment-friendly and safe for nature and people. But we’re more interested in their practical application, the more so that many organic products are also synthesized with the artificial chemicals.

The advantage of organic fungicides over inorganic ones is that that they do not contain harmful and rare metals. These metals are dangerous for animals, earthworms, and in rare cases for the soil, should it accumulate too much copper or mercury. But "natural products" are decomposed under the ground, and it happens very quickly.  Frankly speaking, this property affects the duration of the healing effect (as the synthetic chemicals’ impact lasts longer).

Organic fungicides are easier to prepare as most often all you have to do is mix the powder or liquid product in the water. Moreover, organic products can be combined with a greater number of pesticides than non-organic ones.

Nevertheless, their simplicity is debatable. Sulfur fungicide can also be prepared at home. The authors of this study examine the popularity of sulfur powder (from ~$5) used as a fungicide.

the best fungicide

The main competitive edge of non-organic products is customer loyalty. It is the copper-, sulfur-, mercury- and chlorine-based products which were first launched on the market, and our ancestors used them. So, a certain habit and tradition was formed. Logically, younger synthesized organic products are supposed to be of better quality, but the catch is that the good old 0.5-0.75% copper oxychloride products are still just as effective as popular synthetic ones against certain diseases.

Are artificial chemical fungicides that scary? Here’s what the USA Environment Agency web page states: “Some of the most tragic epidemics of pesticide poisoning occurred by mistaken consumption of seed grain treated with organic mercury or hexachlorobenzene.  However, most fungicides currently in use and registered for use in the United States are unlikely to cause frequent or severe acute systemic poisonings.”

You can only therefore do harm to yourself and environment if you don’t follow the manual when using these products. On the web site it is required to be especially careful with the following substances:strobilurins, thiocarbamates, dithiocarbamates, thiophthalimides, triazoles, organomercury, organotin, and cadmium compounds.

5 Fungicide Purchase Tips

  1. First and foremost, diagnose the disease correctly. Try to diagnose your plant correctly in conformity with the external symptoms, by consulting peers and professionals. Try to obtain a product which suits this particular type of fungus, and not a versatile one.
  2. Pay attention to the environment, such as the place of growth of an infected plant, season, air temperature at the moment of treatment, disease spreading pace. All of these factors will influence your fungicide choice. Often you’ll find the appropriate recommendations regarding optimal use conditions on the label.
  3. Learn about the contraindications. Good quality products list the plants which cannot be treated with said fungicide.
  4. Choose between a liquid and a powder. Powders are better for treating the soil, while the liquids are good at treating leaves and flowers. The liquids’ effect is seen earlier, but as a rule, it lasts shorter.
  5. Compare the price. The prices for the same product or for different fungicides with the similar ingredients can differ greatly. Just like with the medicaments, you don’t always have to spend much on an overpriced brand, if there is a cheap analogue available. However, remember to check that all of the goods are certified in accordance with the state standards.

9 Fungicide Use Tips

Even organic products can harm plants and humans if used incorrectly.  Here are 9 tips on their correct use for amateur gardeners. 

  1. Always follow the safety rules in the manual. Wear protective clothes when spraying. Most often fungicides are a threat to skin and mucous membranes, so even pot plants are to be processed outside or at least on the balcony.
  2. Watch the season. It is considered that the derivatives of dithiocarbamic acid, for instance, have a positive effect on plant growth and development, and so they are usually recommended for use during the period of intensive growth (in the spring and early summer).  By the end of the summer copper-containing products are to be used.
  3. Don’t mix organic fungicides (captan, zineb, ziram, polycarbocine, dichlone) with mineral oil formulations, as such a mixture can lead to plants’ burns.
  4. Keep a treatment schedule. Most often repeat plant treatment is effected once in 15-30 days. Each product has its own treatment rules which are stated on the label. Seasonality and rainfall influence the periodicity as well.
  5. Don’t poison your harvest. It’s better to solve the fungus problem beforehand rather than use the fungicides when the crops ripe. If the problem has been neglected for a long period of time, use products low on toxins and find out earlier how many days before the harvest you can treat the plants for the last time.
  6. Spray in the morning. University of Georgia experts assure that night and small hours of morning are the best time for spraying liquid fungicides.
  7. Watch out for the weather. It’s better not to use sprays, liquids and all products which work on contact when it’s windy or raining.
  8. Mind the phytotoxicity. Phytotoxicity is the state which occurs when the treatment begins to harm the plant. The reason for this is improper substance concentration, frequent usage of artificial chemicals and incompatibility of a product and a plant.
  9. Don’t let them adapt. Resistance is often observed. The fungi simply evolve and their upcoming generations are fungicide-resistant. In such cases Australian scientists recommend either combining the products or eliminating the fungi before they spread all over the place. They also advise poisoning the seeds.

Powdery Mildew Treatment Fungicides

Mildew spores are transmitted through the air, water, and a handshake.  They love damp and cool weather, and adore houseplants.  Too frequent watering of the plants and high rate nitrogen found in the soil can lead to issues.

powdery mildew on plants

During the initial stage (prevention and first week) traditional methods can be used, for example, a potassium solution bicarbonate and soap copper solution or broth horsetail. Lots of such recipes can be found on the Internet.  However, if you miss the right moment, use more serious products.

Dr. Sharon M. Douglas from Connecticut Agricultural Experiment Station lists many options. First of all, she recommends taking a complex approach to plant treatment. Second, she reminds us of the necessity to begin spraying once early symptoms of a disease are seen. She considers neem oil, insecticidal soap, hortucultural oil and the same old potassium bicarbonate to be the type of useful biorational compounds. As for the artificial chemical compounds, the doctor recommends paying attention to copper, fenarimol, myclobutanil, propiconazole, triadimefon and sulfur.

Cannabis Powdery Mildew

Very often powdery mildew attacks cannabis. The spores of fungi causing the disease are widespread.  The predisposing factors of the disease are high humidity and high temperature, which are found in the places of hemp cultivation.

You can find a product suitable for your fungus-infected species in the recommended fungicide chart by Elizabeth Little, Extension Homeowner IPM Specialist. By the way, in this chart chlorothalonil  and   thiophanate methyl are added to the list of effective chemicals. Both of them take a complex approach: they protect the plant and kill fungus on contact.

As for specific products against powdery mildew, Elizabeth recommends the following product range:

  1. Systemic fungicides: Spectracide Immunox (several), Ferti-lome F-Stop Granular Fungicide, Green Light Fung-Away Systemic Granules
  2. Water-based systemic fungicides: Ortho Lawn Disease Control and Ferti-lome, Liquid Systemic Fungicide, Bayer Advanced Fungus Control.
  3. Protective fungicides: Bonide Copper Spray or Dust, Bonide Liquid Copper, Dragon Copper Fungicide, Hi-Yield Copper Fungicide, Ferti-lome Black Spot & Powdery Mildew control.
  4. Protective fungicides acting on contact: Ortho Garden Disease Control (Daconil 2787), Hi-Yield Daconil Lawn Vegetable, Flower Fungicide, Fertilome Lawn & Garden Fungicide, Ferti- lome Broad Spectrum Liquid Fungicide and Bonide, Fung-onil, Ortho Dormant Disease, Control Lime-Sulfur Spray, Hi-Yield Improved Lime, Sulfur Spray, Lilly Miller, PolySul Summer and Dormant Spray, Bonide LimeSulfur.

Lawn Fungus Control Products

Most of the lawn diseases are treated in the same way despite the symptomatic difference. The quality of drain systems matters most when preventing and eliminating them. It should remind you neither of a swampy marsh nor of an African desert. The gardeners recommend watering the plants early in the morning so that the soil could absorb the moisture during the day. Often fungi attack the lawns which are often and intensively mowed. Any cut is a fungus attack risk trigger. It is also known that young grass has weaker immunity than older one. Note that fungi hate heat, which means they are easier to treat in the summer.

All of these are mere prevention measures, though. You will ask what kind of prevention measures are recommended by specialists? Williamson Country Center experts recommend the following products when you come across the lawn root rotting: Spectracide immunox, Ferti-lome Systemic, Ortho lawn disease control, Propiconazole. The majority of them are water-based systemic fungicides. If the grass has colored circles, try using Turfcide, Spectracide immunox, Hi-Yeld Maneb and Green Light broad spectrum. Here powerful products of wide action range are at stake. However, some complex fungicides can also do the trick.

Elizabeth Little’s chart, which is familiar to us, adds more to this list. For example, you’ll see there Bonide Mancozeb Flowable with Zinc (which is a protective product) and Bayer Advanced Fungus Control (which is a popular systemic fungicide).

Snow Mold Treatment Fungicides

The distinctive feature of snow mold in comparison with most of the fungal diseases is that it attacks the plants all the way in winter. The fungus settles in the lawn once it’s cold and snow starts falling, as the familiar to us Dr. Sharon M. Douglas states. You’ll only see the display of the disease in spring and summer when young grass will grow. The owner of the lawn will have time to prevent the epidemic. First, you’ll have to remove traces of old greenery in late fall in order to eliminate the base for the possible airborne fungi attack. Second, you’ll have to remove all the natural debris and carry out the proper mowing of young grass in spring again.

lawn fungus control

There are quite a few preventive fungicides against this problem. The experts recommend the following product line (most of which are granule artificial chemicals which are to be dissolved in the water): Terraclor 75WP, Ferti-lome Azalea, Camellia, Crape Myrtle Insecticide and Fungicide, Hi-Yield Turf and Ornamental Fungicide (containing 10% PCNB), Hi-Yield Terraclor Granular Fungicide (below we’ll give a detailed description of them).

DMI fungicides, strobilurins and dicarboximides are also suitable for autumn prevention. You are supposed to treat the soil with them at the very end of the season.

For plantations protection the familiar Ortho Garden Disease Control (Daconil 2787), Hi-Yield Daconil Lawn Vegetable Flower Fungicide, Fertilome Lawn & Garden Fungicide, Ferti- lome Broad Spectrum Liquid Fungicide and Bonide Fung-onil will do.

You can find loads of useful information in the “A fresh look at fungicides for snow mold control“study. The authors carried out an experiment for 3 years and they note the difference in action of various chemicals on gray and pink snow mold:  “Banner Maxx, Terraneb SP and Bayleton 50WSP (triadimefon) yielded acceptable levels of disease control against speckled snow mold and gray snow mold, but Revere 4000 4F, Terraneb SP, Compass 50WDG (trifloxystrobin) and Bayleton 50WSP were more effective on pink snow mold”.

Best Ready-to-Use Fungicides

The experts approve of dozens of different fungicides, and it is easy to drown in the long list of names. That’s why we decided to help you and picked the most effective products that can be purchased online.

Bonide 811 Copper 4E Fungicide 16oz (473ML)

 bonide fungicideThis is a classic copper-based fungicide suitable for flowers, fruits and vegetables. It treats well the powdery mildew, black spots and early blight.  It is to be mixed with water in the proportions outlined on the package and to be sprayed. The customers claim that one spraying session per month is enough, but the product should be used more often if it rains often or if the plants are frequently watered.

Here’s J. Haglin’s (a customer’s) comment: “I have used it for the last couple years on my tomatoes and cucumbers, and it really works. Start using it early, even before any signs of disease appear and continue to spray it on every week. Rotate your crop so that you aren't planting in the spots where you had blight last year, it will remain in the soil from year to year”.

There are a few mentions of the effectiveness of the product against lawn fungi. Still, around 85% of the customers consider this product useful and rate it at 4.5 stars out of 5 on Amazon.com

Price: ~$16.99 Check the current price

BONIDE PRODUCTS 775 Ready-to-Use Copper Fungicide, 32-Ounce

bonide fungicideThis is a similar product by the same manufacturer. This one isn’t to be dissolved in the water, as it is sold as a ready-to-use spray. The fungicide contains copper octanoate, which is a copper salt combined with a naturally occurring fatty acid. The concentration level of the chemical is aimed at protecting the greenery from burns.

The manufacturer insists on spraying the leaves abundantly. You can treat their bottom. Customers in the comments section don’t advise spraying it before the rain, as its complete absorption takes 24 to 48 hours. Next time you’ll have to spray it after 2-4 weeks.

Here we find a few displeased comments as well. The solution seems to be "rather weak” for some farmers: "The product itself did not help against the fungus attackng my garden. I unfortunately lost all 12 of my tomatoes, the beans, and pepper plants. My tomatoes developed black spots on them and rotted on the vine. The leaves on the tomatoe plant and bean plants turned yellow, developed spots and turned brown and died. Whatever this was it devastated my crops. It swept through and I had little return on my harvest. I thought the copper would help but it was not enough.I need copper oxide this was all I could get ". But this is a particular case, as about 80% of users were satisfied with the operation of the chemical.

Price: ~$13.69 Check the current price

Spectracide 51000 Immunox Multi-Purpose Fungicide, 16-Ounce Concentrate

best ready-to-use fungicideThis is a versatile fungicide that is highly rated by the users with the 4.4 stars out of 5 rating on Amazon.com. It is suitable for most garden plants and lawns. It is especially highly rated by the fans of roses. Here is a list of diseases against which Immunox acts: anthracnose; black spot; blight; brown patch; copper spot; crown rot; dollar spot; leaf smut; leaf spot; melting out; necrotic ring spot; powdery mildew; red thread; rust; scab; spring dead spot; summer patch.

It is protective fungicide which is best suited for prevention and protection of plants against fungus. This artificial chemical is not washed away by the rain and remains on the leaves for two weeks. Depending on the purpose of application (treatment, prevention, protection), the manufacturers recommend using three methods of applying the product: with pump-up Sprayer, dial-style hose-end sprayer and plus water-style sprayer concentrate.

Judging by the reviews, one bottle is enough for treating 500 square feet. Customers write that it works best with the delicate plants and small leaves. Many reviews are devoted to the successful lawn disease control.

Price: ~$17.30 Check the current price

Bayer Advanced 708480 Serenade Garden Disease Control Concentrate, 32-Ounce

Bayer FungicideBayer is the renowned manufacturer, and the quality of its products is unlikely to be questionable. This systemic organic fungicide rated at 4.1 stars out of 5 on Amazon.com not only prevents, but also treats the diseases. Almost 80% of the users are satisfied with its effectiveness. It controls black spot, powdery mildew, rust, gray mold, late blight and scab. Although the manual states that it can be applied for up to a few days preceding the harvest, we wouldn’t take such a risk.

A single bottle will last for 32 gallons of water. The mixture can be applied on both leaves and fruits. In the comments section we were able to find contradictory feedback regarding the necessity of repeat application. Some customers claim that they were able to solve the problem after single treatment, while others insist on compulsory repetition of the procedure after 1-2 weeks. Perhaps, everything depends on the type of fungus and the extent of plant contamination. Fortunately, the fungicide is harmless for worms and useful insects.

Price: ~$13.90 Check the current price

Daconil® Fungicide Concentrate 16 oz.

Daconil FungicideThis is an expert-proven сhlorothalonil-based product. It is perfectly suitable for powdery mildew treatment. All of the ingredients are listed on the package, and they can all be looked up on the Internet if needed. A single bottle is enough for 64 gallons of liquid to be sprayed. The product is considered to be protective fungicide acting on contact and of a wide range of action. However, as it can result in phytotoxicity, it’s not recommended for pittosporum or schefflera.

Although the fungicide’s Amazon.com rating is very high, and is 4.4 stars out of 5, we were able to find some ambiguous comments, such as this one, by a gardener: “It does a good job against phyllosticta minama (leaf spot), however it left the tree coated in a milky white film, which looks almost as bad as the leaf spot. This is not a systemic medication so its use is limited. Other concerns are its highly toxic effects on many aquatic animals, dead fish and frogs. Chlorothalonil is not thought to be toxic to adult bees. However, it’s known to be an extremely toxic pesticide for honeybee larvae”.

Price: ~$20.38 Check the current price

Scotts Lawn Fungus Control, 5,000-sq ft, 6.75 Pounds

 fungus controlThis is a product rated at 3.9 stars out of 5 on Amazon.com and is devised especially for lawn disease prevention. A 2.3% thiophanate-methyl is the active ingredient here. Experienced users recommend using the product in the spring, otherwise it may be too late, as Scotts Lawn won’t be able to remove the fungus. A single bag is enough for 4-5 thousand sq. ft. Note that the customers’ opinions regarding this product differ. Some believe it’s too toxic for home use. Here’s what bookbrook has got to say: “I didn't realize how toxic this chemical was until I looked it up online after applying it to my lawn. Please be very careful when applying and make sure to keep your children and pets off of it for a while after you apply it. I don't know how long this stuff stays at toxic levels in your lawn. The customer service rep I called about it told me to wet the area the chemical was applied to and then once it's dry that it's safe for children and pets to resume using the area - but you never know.”

Price: ~$23.77 Check the current price

Potassium Bicarbonate, a Traditional Homemade Fungicide

Potassium bicarbonate is an organic chemical compound (KHCO3) looking like white powder widely used in various industries: medicine, sport, cooking and even agriculture. This protective fungicide is a real salvation for the plants growing in acidic soils as it:

  • Is low on toxins;
  • Protects the veggies (pumpkins in particular) and decorative plants from powdery mildew;
  • Inhibits the breeding of harmful fungi and bacteria.

BUT! Potassium bicarbonate won’t protect you from black spot on roses and from direct contact of the plants with fungi.

Why is it often used as a replacement of baking soda (NaHCO3) for treating the plants? Based on its chemical composition, it seems that the difference between them is almost non-existent and their chemical properties are similar. But this is only a first impression.

It is known that when in contact with the ground, both baking soda and potassium bicarbonate eventually settle therein as chlorine salts which are useful for plant nutrition and growth, but an excess amount of which can cause substantial damage (sodium soda can be especially harmful). That’s why you cannot use these fungicides haphazardly! Treating the plants with them is possible only in certain seasons, spring or fall, depending on the soil type. You can use any of them, but potassium bicarbonate is considered more effective than baking soda. Studies conducted by American scientists from the NCBI show that “the applications of potassium bicarbonate (as Armicarb) are effective in reducing the incidence and severity of American powdery mildew in gooseberry”. According to the experiment carried out, the rate of plant infection decreased from 90 to 10% given the constant spraying.

Potassium Bicarbonate

Unlike potassium bicarbonate, baking soda doesn’t eliminate powdery mildew on plants, but only prevents its spreading. This fact was noted multiple times by the gardeners using it as a fungicide and comparing its action with that of potassium bicarbonate. In spite of the fact that soda has been used as a fungicide for over 80 years, Purdue University specialists have also found out that “baking soda can be effective against plant diseases when used with oil, its sodium component can build up and become toxic to plants”

That’s why we believe that the choice between potassium bicarbonate vs baking soda is quite obvious.
Here’s a popular fungicide recipe based on potassium bicarbonate:

“Mix 4 teaspoons (about 1 rounded tablespoon) of potassium bicarbonate with one gallon of water. Spray lightly on foliage of plants afflicted with black spot, powdery mildew, brown patch and other fungal diseases. Potassium bicarbonate is a good substitute for baking soda. There are commercial EPAs registered as well as generic products available”.

The bicarbonate itself can be bought at a moderate price of ~$7.90 per 1 Lb.