Sulfur Fungicide: Disease And Pest Control Option

A good sulfur fungicide can be used for everything from spider mites to treating powdery mildew. We discuss how it works in the garden!

Sulfur fungicide


Fungicides can save you from certain pests and diseases from destroying your garden. Sulfur fungicide can reduce or prevent Alternaria leaf spot, powdery mildew, rust, chiggers, and many other problems that might show up in the garden. It sounds like a lifesaver, right?

You need to know a few things before you douse your plants in sulfur fungicides. For starters, those who live in hot climates shouldn’t apply it when the temperature exceeds 85°F (32°C), or it will fry your plants! Using it a couple of weeks before or after applying oils such as neem oil will also lead to fried plants, as well. There are also a few safety concerns to be aware of that we’ll get into in a bit. But, the good news: it’s generally believed to be non-toxic to honeybees!

While the downsides may seem like a lot to deal with, especially if your summers consist of triple-digit temperatures, you should still consider adding a sulfur plant fungicide to your gardening arsenal. When you use it as intended, it will do you a world of good – especially when you’re battling leaf spot, powdery mildew, or other damaging things like scale or chiggers!

Good Options At Amazon For Sulfur Fungicide:

What Is Sulfur Fungicide?

Sulfur fungicide
Sulfur fungicide can be mixed with water and sprayed, or applied as dust. Source: RobynAnderson

Sulfur has been used to treat diseases such as powdery mildew for years and years. It’s said that Homer, the Greek author, mentioned the use of sulfur as a pest control method as early as 1000 BC. This isn’t just “Grandma’s old gardening tip” we’re talking about!

Today, sulfur is most commonly available as a fine powder that you can sprinkle directly on plants or mix with water to form a spray. One of the most popular products you’ll find is Bonide Sulfur Plant Fungicide. It’ll come in a bag or a bottle you can easily squeeze or shake, and is a micronized form that’s super-fine and easy to blend into water. Sulfur fungicide is also available as a ready-to-use (RTU) spray, which is handy if you don’t want to deal with the powder yourself.

Sulfur is naturally occurring in the earth, so it’s a completely organic option that won’t harm the environment for the most part. If companies add other ingredients to their products that are chemically derived, it may or may not qualify as an organic option depending on what was added.

Sulfur will increase the soil’s acidity, which is problematic for some plants you may have in your garden. But that’s where lime sulfur comes in. Lime is added to sulfur to cut down the acidity so it won’t affect the soil as much. Lime sulfur treats the same diseases and pests as regular sulfur fungicides, so the only difference is how it affects soil pH.

How Does It Work?

Apply sulfur spray or dust to leaf surfaces and stems, and this product controls and may prevent diseases like powdery mildew from developing, and may also kill some pests. Easy peasy!

It isn’t totally understood how sulfur stops diseases such as fungi, but it’s believed that it disrupts the metabolisms of fungi which stops them from spreading, and it can kill spores on contact. It’s most effective when it’s applied before diseases show up since they can kill them at the beginning.

Sulfur also kills insects whether they touch it or consume it. It disrupts their body’s ability to produce energy and eventually kills them. When treating pests, you don’t have to use this as a preventative measure. You can apply it when you see pests as long as all the other conditions are right for the application.

Benefits Of Using Sulfur Fungicides

Elemental sulphur
Elemental sulfur, or sulphur as it’s spelled abroad, is a mineral. Source: Rob Lavinsky

Many pesticides harm wildlife and beneficial pollinators, so it can be tricky to find something safe to use in the garden. Fortunately, sulfur is non-toxic to honeybees, birds, and fish! You don’t have to worry about harming pollinating visitors or backyard ponds with organic sulfur plant fungicide, so you can feel good about using it in your garden.

Since sulfur occurs naturally in nature, it’s not a big deal if it touches the soil. It will break down and rejoin the natural sulfur cycle of the earth. It doesn’t dissolve in water, so water runoff can be an issue, but we’ll talk more about that and safety concerns in the drawbacks section.

Pests/Diseases Treated By Sulfur

Sulfur fungicides can treat several diseases on fruits, vegetables, and ornamental plants. It can treat Alternaria leaf spot, powdery mildew, rust, black rot, brown rot, scab, and blossom blight. Be forewarned that if rust, scab, brown rot, or leaf spot damage is already present on the plant, it will not cure the damaged tissue, and you definitely want to prune off severely-damaged foliage and dispose of it. This can be problematic in the case of brown rot especially, as you have to take off the damaged tissue at least five or six inches below the visible rot. In the case of powdery mildew, it may help leaves to regain some of their vivacity, but it’s still best to prune severely damaged leaves away. Blossom blight will usually cause the blossom to drop no matter what you do to treat, but the plant may flower again.

It can also treat a wide array of pests, including thrips, scale, ticks, red spider mites, the two-spotted spider mite, and other pest mites like broad mites.

You can use sulfur fungicides on most plants, including some types of berry crops, roses, ornamentals, and most leafy or fruiting vegetables. There are exceptions in each of these groups because some plants are intolerant of sulfur and can be damaged or killed if they’re exposed to it!

Drawbacks Of Using Sulfur Fungicides

You have to use sulfur fungicides carefully because there are some plants that can’t handle it. In addition, it will burn plants if the temperatures are too hot or if it’s mixed with oils, and it’s somewhat toxic for humans and pets.

You shouldn’t apply sulfur if the temperature is 85°F (32°C) or higher, or if the temperature is going to reach that high later in the day. This can certainly be annoying if your summers are always 85°F or above, but you can still use it in cooler months with fewer problems.

If you apply neem oil to your plants, you should wait at least two weeks before you apply sulfur, or the two will combine to burn your plant’s leaves in a similar way to sunscald.

Sulfur might be safe for bees, fish, and birds, but it’s slightly toxic to humans and pets! It can irritate your eyes and skin if you come into contact with it and can irritate your respiratory system if you breathe it in. It’s often in the form of dust with an extremely fine particle size, so it’s unfortunately easy to breathe in or get in your eyes. Always wear protection when you’re handling it and don’t use it around kids or pets.

Speaking of pets, don’t let your furry friends consume this fungicide by snacking on your plants. If they eat too much sulfur, it can cause severe health concerns. If your pets roam freely through the garden, this may not be an ideal solution for you, and something like neem oil will be a safer option.

We mentioned earlier that sulfur dust doesn’t fully dissolve in water, which is a problem. It won’t impact the environment too much but can gradually acidify your soil. In addition, if the water runs off into a field or flower bed of plants that can’t tolerate sulfur, you may have problems! What plants can’t tolerate it? Let’s take a look.

Plants At Severe Risk From Sulfur

The plants that can’t tolerate sulfur include apricots, cherries, peaches, nectarines, plums, and other stone fruits; raspberries, boysenberries, gooseberries, blackberries, and other soft berries without a thick skin; cucurbits, Cox’s Orange Pippin apples, Delicious apples, Eastern American grapes, and currants. These plants are highly sensitive to sulfur and can be harmed or die if they’re exposed to it. Certain types of exotic citrus may also be impacted, although most citrus should be fine to treat.

You can still use sulfur in your garden even if you have these plants. You’ll just need to be extra careful when applying it to avoid it blowing onto these species. Never apply the dust or spray in the wind, especially if the wind is blowing toward sulfur-sensitive plants. If your yard is sloped and water runs off in a certain direction, avoid planting the intolerant plants where the water collects.

How To Use It In The Garden

Sulfur-dusting of grape vines, 1972
Crop-dusting with sulfur fungicide has been happening for almost a hundred years. Source: National Archives at College Park

Sulfur is super easy to use in the garden. If you don’t want to mix up your own spray, you can buy an RTU product or apply the dust directly to the plant with a handy squeeze bottle. 

If you’re going to create your own spray, follow the directions on the product label of a reputable brand, such as Bonide Sulfur Plant Fungicide. Different products might have specifications that could affect plants both positively or negatively. Generally speaking, the ratio is typically about three tablespoons per one gallon of water and mix well. Remember, the powder won’t fully dissolve in the water.

You can spray this mixture onto fruit and leaf surfaces of many plants such as blueberries, citrus, strawberries, and any other plant that isn’t sensitive to sulfur. The mixture will dry and leave the powder behind, and it will prevent diseases and kill pests for a couple of weeks.

Ready-to-use sprays can be used just like a DIY mixture. The only difference is that you don’t have to mix it yourself. Powders can be applied directly to plants in a similar manner, but it may be more difficult to reach the undersides of leaves and stick to stems. One thing to note about sulfur dust is that it’s better for treating tiny little mites. Sulfur is natural, so if it touches the soil while you’re trying to get those hard-to-reach areas, it’s not a big deal.

The best time of year to start applying sulfur is in late winter or early spring before foliage appears and diseases develop. Once leaves start growing, apply the fungicide early in the morning so sprays can dry and so they won’t burn the leaves. Remember, hot temperatures can cause leaves and fruits to burn, so it’s best to avoid applying it during the hottest parts of summer.

You can apply sulfur every 10-14 days as needed or after it rains. Rain will wash everything away, and you’ll have to start the treatment over. If you need to apply neem oil, you’ll need to wait a couple of weeks after applying sulfur, apply the neem oil, and then wait two more weeks before applying sulfur again. If your memory works against you sometimes, you may benefit from a little calendar to keep your treatments in order!

Frequently Asked Questions

Q: Is sulfur a good fungicide?

A: Sulfur is an excellent fungicide to use because it can treat a wide variety of pests and diseases. It can be a bit finicky to work with since certain plants are intolerant, and it will burn leaves in hot temperatures, but it’s a valuable and reliable addition to your repertoire of pest and disease control.

Q: How often can I spray sulfur?

A: You can spray sulfur every 10-14 days. You’ll need to apply it sooner if it rains, and you’ll have to wait two weeks after applying neem or other oils since oil and sulfur together will burn plants.