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Posted on Dec 20, 2017 in Disease | 0 comments

Organic Fungal Disease Sprays

Organic Fungal Disease Sprays

Fungal disease on your fruit and veggies doesn’t have to mean the end of your crop.

Organic fungicides have proven themselves to be highly effective in treating common garden fungal infections. Additionally, many can be made easily and safely using common household ingredients, for a fraction of the cost of chemical fungicides.

Chemical fungicides can affect beneficial micro-organisms in the soil and kill pollinators and predatory insects. This can affect the natural balance in the garden and cause additional problems down the track.

Sources of fungal disease

Fungi are most often spread by wind and water splash with contaminated soil and plant materials.

Fungal spores can be introduced or spread by animals, people, tools, seeds and seedlings, weeds and other plant material such as plant debris left behind at the end of the growing season. The disease enters plants through natural openings and via wounds caused by pruning, harvesting, insects and other garden diseases.


Always follow sound cultural practices to prevent or reduce pest and disease problems in the first instance. This includes:

  • Crop rotation – rotating crop families through the garden beds
  • Building healthy soil rich in organic matter (adding organic plant food through the growing season)
  • Watering regularly and deeply (at soil level) – Avoid wetting foliage
  • Mulching to protect foliage from soil borne diseases splashing onto foliage during wet weather
  • Disposing of diseased plants outside of your garden system i.e do not compost diseased plant materials
  • Maintaining good airflow around plants i.e. don’t overcrowd plants and stake or provide support for sprawling crops e.g. tomatoes and cucumbers
  • Disinfecting tools between cuts to prevent spread of disease
  • Washing hands after touching infected plants and before touching unaffected plants
  • Managing garden pests
  • Planting disease resistant cultivars.

DIY fungicides

Most fungicides are protectants and will only protect the uninfected foliage they are sprayed onto. They have limited systemic activity, and will not protect new growth occurring after application.

For best results, do not wait for the disease to take hold. Prevention or early intervention is required for success.

You can either apply sprays an a preventative or wait for first sign of disease, remove affected leaves, then start applying regular treatments (my preference). I’ve found the home made remedies below to be just as effective as chemical fungicides. For best results, be sure to cover all plant surfaces with spray.

Note: Sprays should only be used as required and at the strengths recommended. Excessive use of organic sprays can disturb the delicate balance of microflora and nutrients within the soil.

Bi-carb soda & Potassium bicarbonate

Effective for: Prevention and control of Powdery Mildew Prevention of Anthracnose in cucurbits and rust

Potassium bicarbonate is the more effective of the 2 bicarbs and has eradicative as well as preventative properties. Potassium bicarbonate is available at garden centres under the trade name eco-fungicide. It is also available from some beer and wine-making suppliers. It is highly effective at Powdery mildew control and as long as you cover all leaf parts with the initial spray, regular sprays are not required. Treat only as required.

Bicarbonate spray (.5% solution)

In a spray bottle, combine the following:

  • 1 litre of water
  • 1tsp of bicarbonate soda or Potassium bicarbonate – this is the active ingredient
  • 1/2-1 tsp horticultural oil e.g. white oil helps the solution to stick the the leaf surface
  • 2 drops of detergent – helps to spread solution

Spray all surfaces of the plant including the underside of leaves. Best used in the evening. Spraying whilst hot can cause leaf damage.

The .5% spray works best in most situations. Higher concentrations can damage leaves of some crops. If the solution is too strong it will damage leaves of sensitive plants such as rockmelon. A stronger solution 1% can be used on grape vines.

Caution: Bicarbonate soda can build up in soil when used in drought-stressed areas where only drip irrigation is used. Increased bicarbonate in soil can lead to removal of calcium and magnesium, and prevent the absorption of iron and lead to iron chlorosis, although the risk is small.

Report showing effectiveness of Sodium bicarbonate on fungal diseases.


Effective for: Powdery mildew

In a spray bottle, combine 1 part organic milk to 10 parts water. Spray all plant surfaces.

Caution: Stronger solutions will encourage sooty mould, so stick to the recipe.

Copper and/or sulphur

Copper sprays

Effective for prevention of fungal and bacterial conditions.

Copper fungicides can been used to treat a wide range of fungal and bacterial diseases in the veggie garden including blights, various spots, mildews, cankers and more.

Examples: Kocide (copper as cupric Hydroxide), Copper oxychloride. Use as directed on label.

Sulphur sprays

Effective for prevention of fungal conditions.

Sulphur is often used as a preventative fungicide, most often on dormant plants. It works by preventing spore germination.

Lime‐sulphur is formed when lime is added to sulphur to help it penetrate plant tissue. It is more effective than elemental sulphur at lower  concentrations. However, it gives off an odour of rotten eggs, which usually discourages its use over extensive plantings.

Do not use sulphur:

  • In conjunction with oil or if you have applied an oil spray within the last month (will damage/kill plants)
  • When temperatures exceed 25°C
  • On cucurbits (pumpkin, zucchini, melons, cucumber)

Examples: Mancozeb. Use as directed on label.

Copper & sulphur combined (Bordeaux mixture)

Bordeaux mixture has been around for centuries. It is used on dormant fruit trees and vines and can prevent mildews and leaf curl (in peaches & nectarines). It contains copper sulphate, which is acidic, neutralized by lime (calcium hydroxide), which is alkaline.

Bordeaux mixture is both fungicidal and bactericidal. As such, it can be effectively used against diseases such as leaf spots caused by bacteria or fungi (powdery mildew, downy mildew and various anthracnose pathogens). Bordeaux mixture’s ability to stick to plants regardless of light rains is one reason for its effectiveness.

Bordeaux spray:

Important: Only use on deciduous, dormant plants as this mixture will cause leaf drop.

  1. Dissolve 100 gram of builders’ (hydrated) lime in half a standard (plastic) bucket of water. (About 5 litres).
  2. Dissolve 100 grams copper sulphate (available at garden centres) in a separate half bucket of water.
  3. Keeping the lime mixture agitated to prevent settling, pour it steadily into the half bucket of dissolved copper sulphate.
  4. If necessary add enough extra water to make up a total of 10 litres. This is Bordeaux mixture. It is at its most effective strength when freshly mixed so must be used immediately or within a couple of days.
  5. It is sprayed to completely cover the main (bare) branches of stone fruit trees to help control leaf curl and brown rot disease.

Caution: Copper and sulphur can cause irritation to skin and mucous membranes in sensitive individuals. Always wear breathing protection and cover skin when using them.

More information: The role of copper and sulphur ‐ based fungicides in organic vegetable production

Organic Fungal Disease Sprays
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