The education spot during the July Working Bee was conducted by Fraser, who explained and demonstrated the use of lime sulphur and Bordeaux spray mixes. He has kindly put together this comprehensive information for everyone’s reference.
Don’t forget that while these are acceptable organic spray mixes (ie. they are derived from organic materials and break down in the soil), any pesticide or fungicide should always be considered as a last resort. The organic grower should be able to mitigate pest problems by prevention, finding the root cause of the problem and altering cultivation techniques to suit. Planting for good biodiversity, allowing pest predators to thrive in the garden and practising crop rotations also go a long way to sorting out your problems.
The following are useful mixes but don’t be frivolous with them. For example, a healthy garden will benefit from an annual spray of Bordeaux as a preventative measure, during the colder months. But a garden with persistant insect problems will not benefit from repeated spraying.
Lime sulphur is sold as a spray for deciduous trees to control fungi, bacteria and insects — living or dormant — on the surface of the bark. Lime sulphur burns leaves, so it is not as useful for evergreen plants.
It is a mixture of calcium polysulphides formed by reacting calcium hydroxide (commonly called “brickies lime”) with sulphur. It can be prepared by boiling calcium hydroxide and sulphur together with a small amount of surfactant (eg. pure soap). It is normally used as an aqueous solution, which is reddish-yellow in colour and has a distinctive offensive odour. Powdered dry sulphur can also be used as a dust to control pests, but the advantage of using it as a wet spray is that it has better coverage and sticking qualities than if used as a dust.
Mix a tablespoon of powdered sulphur with a cup of slightly soapy water, strain and spray. The adding of lime to sulphur gives the added benefit of penetration into the bark layers, which gets to those hidden eggs and spores and also has a residual effect.
Lime sulphur is believed to be the earliest synthetic chemical used as a pesticide, being used in the 1840s in France to control grapevine powdery mildew. In 1886 it was first used in California to control San Jose scale. Commencing around 1904, commercial suppliers began to manufacturer lime sulphur; prior to that time, gardeners were expected to manufacture their own. By the 1920s, essentially all commercial orchards in western countries were protected by regular spraying with lime sulphur. However by the 1940s, lime sulphur began to be replaced by synthetic organic fungicides, which risked less damage to the crop’s foliage.
It is a popular fungicide for the organic gardener and is not only a powerful fungicide but is also effective against scale, red spider mites and can be used in higher concentrations to kill eggs of various pests in winter, particularly on deciduous fruit trees. It is particularly valuable for blister mite on grapevines and for brown rot on peaches and nectarines.
Do not use on apricots and some apples have sulphur sensitivity. It is not compatible with most other pesticides. Do not use within 10 days of oil sprays.
This fungicide has been in use for more than a hundred years. It is very effective against a wide range of diseases and sticks onto the plant well. It must be mixed fresh on each occasion and used within an hour or 2.
Copper in small concentrations is essential to both plant and animal life and it is an important trace element in soils, but it is also essential to remember that excessive copper will kill most forms of life. The danger of overuse of copper sprays is in the continuous application year after year, which can cause imbalances in the soil. A build up over years may cause copper toxicity, so while it is a good fungicide on fruit trees or tomatoes, it is also a powerful fungicide on the essential microflora of the soil. TAKE CARE. Even consider drop sheets to protect your soil.
To make, mix 90gm of Copper Sulphate (bluestone) with 6.5 litres of cold water in a non-metallic container (plastic, glass, wood, clay). In a separate non-metallic container mix 125gm of slaked lime (brickies lime, calcium hydroxide) in 2.5 litres of water. Do not use agricultural lime, as this is a different calcium compound and you will damage your plants. Mix well and ensure that each mixture is fully dissolved.
Combine the 2 mixtures and stir well. Test the mix by putting an old nail (not galvanised) into the mix for 30 seconds. If it comes out blue, try mixing more thoroughly to dissolve the lime, and if this doesn’t work you need to add more lime mixture, also properly dissolved in the correct proportions.
Use the spray within an hour of making it and keep agitating the spray tank. You may want to adjust the quantities given above. For example, at the SAGE working bee, we made half the quantity above (to give us 4.5 litres of Bordeaux) but we only needed half that for about a dozen young trees, so work it out.
In addition to the cautions already mentioned, do not mix Bordeaux with any other pesticides, do not apply within 2 weeks of a lime sulphur spray and do not use on delicate leaves. Do not mix in metal or galvanised buckets. Rinse your spray equipment thoroughly as lime can clog spray heads etc.
Use at bud swell for deciduous plants, after blossoming for evergreens and throughout the season for controlling downy mildew on grapes and veggies, but at half strength. Don’t spray in hot weather. Anytime during the day is fine in the cold months, but wait until the cool evening, if spraying in hotter months.
Make sure you spray all the bark, including the crutch. If you spray before all the leaves have dropped off then you may need to spray again, as infection may enter at the newly exposed areas.
The above information has been collated from the following resources:
- The Best of Jackie French
- Organic Gardening by Peter Bennett
- What Garden Pest or Disease is That? by Judy McMaugh