Treating mould and fungal infections on plants

Going.Local
Published on September 10th 2020
9
A close up of a piece of wood with fungus
Mould, or more specifically fungal infection, is something every gardener dreads. It sneaks in and kills off your plant, leaving you to wonder what you did wrong.
Let me set your heart at ease and tell you, everyone, no matter the level of plant expertise, will find fungi infecting their plants. The key is spotting it early on so you can treat it. Now put on that white coat and let's treat your plant!
A close up of a tree and mushroom
There exists 70 000 described fungal species and the number keeps growing each year.

Common misconceptions

"You overwatered it."
Fungi tend to feed off dead tissue, so it is possible that dried up/dead tissue from under-watering, can attract fungi once watered.
"You did something wrong."
Sometimes you can have a single snout beetle or insect snack on your plant, opening it to infection. Heavy rain for a couple of days can have the same effect.
"It can not be fungal because it recovered by itself."
Some fungal infections will die off if the season changes or when exposed to sunlight/windy conditions (desiccation).
"Rot is due to fungi."
Plant tissue can rot due to both fungal and bacterial activity. Bacterial rot develops faster, with the plant tissue turning a soft mush.
Fungal infection on an asclepiad

Identifying fungal rot

All fungi are NOT equal. Fungi are in a kingdom of its own, like plants or animals. Some produce edible fruiting bodies, like white button mushrooms, whilst others produce soft carpets of dangerous spores.
The best way to identify your problem fungus is to look at how it has infected your plant.
Can you answer these questions:
  • Do you have black, brown or orange spots/circles?
  • Do the spots appear on the surface or sunken?
  • Does your plant suddenly have a fluffy appearance?
  • Do you have leaf curl or wrinkled leaves even though you watered it?
  • Are the roots black?
If the answer is yes, then you might well have a fungal infection. If you have gotten this far, then the next step is to stop the spread. If the fungus is growing on the surface, you should be able to treat it easily. If it has infected the roots or deeper tissue, then you will need to remove this tissue or apply a systemic fungicide. More on that below!
Fungus infecting succulent

Treating fungal infections

Do not despair just yet, as you might be able to save a portion of your plant. As with most diseases, it is important to catch it in the early stages.
Here is a list of the most common antifungals with their pros and cons. They fall within three classes: Systemic, Contact and Biofungicides. Systemics will enter via the roots and remain in the plant for a period between 1-5 days, while contact fungicides are applied to the surface and will also degrade over time.
A close up of a green plant with fungus
When a fungus is growing on the surface of a plant one can use a contact fungicide or make a homemade one with baking soda or peroxide.

Contact fungicide

Peroxide - Hydrogen peroxide can be applied to soil (3%) or leaves (0.06%).
  • Pro: It is non-corrosive and will kill both bacteria and fungi.
  • Con: It will kill beneficial bacteria in soil and degrades in sunlight (make fresh & keep in dark area).
Cinnamon - The ground spice can be applied to exposed cuts.
  • Pro: It is easily accessible and on hand
  • Con: It only works on a subset of fungi.
Baking soda - Used at 20-40g/L in water.
  • Pro: Has been shown to work against yeasts, mould and dermatophytes.
  • Con: Need high concentrations and it affects the pH.
Sulphurs - Sulphur powder applied to the exposed area.
  • Pro: Works well on wounds.
  • Con: Need high concentrations to be effective.
Copper oxychloride - Follow instructions provided.
  • Pro: Works well for bacterial and fungal diseases in fruit trees.
  • Con: It can be harmful to humans and pets.
Fungicides - Mancozeb, Propineb, Captan, Chlorothaonil (Odeon).
  • Pro: Works well on target fungi.
  • Con: Toxic and can affect the local microbiome.
Fusarium infection of succulent
Fusarium enters via the roots to set up shop in the vascular system. Severely infected tissue should be removed entirely.

Systemic Fungicides

Systemics are convenient as they can be applied to surfaces and be taken up by the plant. Note that some may affect the plant physiology (i.e. slower growth or flower formation) and should be handled with care.
Some over the counter products will have a mixture of more than one compound, such as Rosecare. It is recommended to switch between fungicides to limit fungi building up a resistance.
Triazoles: Penconazole, Tebuconazole (Orius 250)
Benzimidazole: Carbendazim
Pyrimidine: Nuarimol, Bupirimate (Rosecare)
*Tip | Always make sure to read the information as some fungicides are toxic to animals and insects. Isolate your plant so that the fungicide has time to break down.
Yeast

Biofungicides

These are bacteria that can be sprayed on infected plants to limit fungal infection.
Bacillus subtilis- Foliar application/Orchids
Streptomyces lydicus- Vegetables
Trichoderma harzianum - Woody or herbaceous plants
A dried and dead fungal infection
Note that dead fungal colonies will change to a lighter color.

Final Notes

It is advisable to try different approaches as fungi can evolve and build up resistance to a certain compound. Note that copper, sulfur and peroxide play a natural role in plant physiology, therefore repeated application can affect the plant's growth and development.
If you have any further questions or found the article helpful then drop us a comment below!

Dig into the diseases profiles below to learn more about various fungi.

Bibliography:
Letscher-Bru, V., Obszynski, C.M., Samsoen, M., Sabou, M., Waller, J. & Candolfi, E. (2013). Antifungal activity of sodium bicarbonate against fungal agents causing superficial infections. Mycopathologia,175(1-2), 153-158.
Petit, A. N., Fontaine, F., Vatsa, P., Clément, C. & Vaillant-Gaveau, N. (2012). Fungicide impacts on photosynthesis in crop plants. Photosynthesis research, 111(3), 315-326.
Swain, S. (2020, 1 September). Biological Fungicides: Do They Work and Are They Safe?. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13543
Yang, C., Hamel, C., Vujanovic, V., & Gan, Y. (2011). Fungicide: modes of action and possible impact on nontarget microorganisms. ISRN Ecology, 2011.
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