What Is the Best Fungicide for Dahlias?

Dahlias are beautiful flowers with many wonderful benefits. They come in many different colors, shapes, and sizes which is great for the gardener looking to add a touch of color to their garden or landscaping.

Unfortunately, they can also be very difficult to maintain as they require a lot of care and attention if you want them to grow successfully.

One way that you can help ensure your dahlias will thrive is by using an appropriate fungicide when needed! In this blog post, we will explore what the best fungicide for dahlias might be as well as the circumstances under which it should be used.

What Is the Best Fungicide for Dahlias?

It’s time to review the best fungicides for dahlias. Here they are:

1) Bonide 811 Copper 4E Fungicide – Copper Octanoate 

This fully biodegradable, OMRI-listed fungicide offers 10% Copper Octanoate (1.8% metallic copper) as the active ingredient, which is what makes it one of the best fungicides for dahlias.

It’s a contact and systemic fungicide that works to protect your plants from a large number of different fungal diseases, including powdery mildew, rusts, Septoria leaf spot, Pythium blight, and more!

Powdery mildew HATES copper! The copper ions harm the fungi or their spores by damaging their cellular membrane and cell metabolism.

2) Garden Safe Brand Fungicide – Neem oil 

This is a dahlia fungicide that can also be used as an insecticide and miticide. If you’ve read any of my other articles, then you will know just how much I love using neem oil. In fact, I use it for nearly all pest and fungal-related issues.

The powerful fungicide will keep your Dahlia clean and free of pesky insects. It prevents fungal germination, as well as suffocating those pests so you can enjoy a beautiful flower without any hassles!

3) Spectracide Immunox Multi-Purpose Fungicide – Myclobutanil

Unlike the two above, this is an inorganic fungicide. However, Myclobutanil (1.55%) is one of the best ingredients for killing fungus on dahlias. This means that it’s great for targeting extreme cases of fungus.

When sprayed over your plants, the ingredient soaks into the leaf tissue and through the phloem and xylem. The myclobutanil works to stop the fungus by producing ergosterol, which controls fungus cell membranes.

This fungicide can be used for a wide range of fungus, but it’s especially effective against things like powdery mildew.

4) Dr. Earth Disease Control Fungicide – Rosemary oil, Clove oil & Peppermint oil 

This fungicide uses three natural oils to get rid of dahlia fungus, which are rosemary oil (0.06%), clove oil (0.05%), and peppermint oil (0.05%).

Each ingredient works together to create a powerful fungicide, which will leave your plant fungus-free. Also, these oils have been known to keep insects away, which is an added bonus!

Rosemary oil is rich in antioxidants and antimicrobial properties that work to protect the plant from fungi. Clove oil contains eugenol, which helps with pest control, while peppermint oil has antiseptic properties to prevent further infections.

5) Southern Ag Liquid Copper Fungicide – Copper Diammonia Diacetate Complex 

Here we have another copper-based fungicide. This one comes with 27.15% Copper Diammonia Diacetate Complex and 8% metallic copper.

This product works great for killing fungus on dahlias and many other plants as well! The only downside is that this isn’t OMRI approved, so it’s not suitable for organic gardening.

However, it will get rid of any fungus you have on your plants without causing them damage or harm in the process!  

What is a fungicide?

A fungicide is a chemical that can be used to prevent and control the spread of plant diseases. It can be used to treat diseases like powdery mildew, rusts, leaf spots, and blights.

When should fungicide be used on dahlias?

A fungicide can be necessary to use on your dahlias if you notice the following signs of disease: yellowing leaves, brown spots spreading across plant foliage and stems, mildew forming on flowers.

How do I apply Bonide Copper Fungicide to dahlias?

To ensure the successful application of this product, it is best to carefully follow all instructions found on its label. This includes thorough coverage of both upper and lower sides of all plant leaves as well as making sure the entire area around the plants has been coated with an even film before allowing them to dry completely.

How often should I apply a fungicide to dahlias?

Apply fungicide to your dahlia if you believe your plant is suffering from a fungal infection, but be sure to check the label for any specific application frequency information.

This product should only need to be applied once per week and could harm your dahlias if it’s properly used according to its guidelines.

The most popular dahlia fungicides are concentrates or ready-to-use products. This means that it’s easy to apply these types of formulas, which makes them easier for first-time users like you!

Will fungicide help powdery mildew on dahlias?

Yes, a fungicide can be very effective at treating powdery mildew on dahlias. It should, however, only been applied once a week to ensure you’re not overusing the product and doing more harm than good.

Is neem oil good for dahlias?

Yes, neem oil is a good fungicide to use on dahlias because it can help prevent and control the spread of plant diseases like powdery mildew.

To ensure you’re using this product correctly, be sure to carefully read all instructions found on its label as well as any supplemental information provided by your local garden center or agricultural department.


In conclusion, dahlias are beautiful and colorful flowers that make for a great addition to any garden. However, they can also be prone to fungal infections if proper care isn’t taken by the gardener!

I hope that this blog post has been helpful in learning more about the best fungicide for dahlias and how you can use it to keep your plants healthy.

If you have any additional questions, feel free to ask them below! I’ll be happy to answer them as soon as possible.

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