Winter is the traditional time to prune and spray deciduous fruit trees and vines. Spraying is carried out at this time to eliminate pests and diseases which can overwinter and emerge in spring.
Two separate treatments are usually employed in winter. Oil sprays are often used to control overwintering pest insects, and fungicides are used to treat the many fungal diseases which emerge during the warm, wet spring season.
Lime Sulphur serves both as a fungicide to control certain fungal diseases and also kills overwintering pest insect, a great convenience to gardeners.
What is lime sulphur?
Lime Sulphur is a reddish-yellow liquid with a distinctive rotten egg smell which is soluble in water. It is a mixture of various calcium polysulphides, and its use is accepted in organic gardening as it’s made by reacting together sulphur and builder’s lime (calcium hydroxide) – which is different to garden lime (calcium carbonate).
It’s quite alkaline, lime sulphur has a pH of 10.5-11.5, it’s considered caustic or corrosive, but to put it into perspective, it’s alkalinity is somewhere between milk of magnesia (pH 10.5) which is taken for indigestion and ammonia (pH 12). At around pH 11, it’s three pH points (10x10x10) or 1,000 times less alkaline than caustic soda with a pH of 14. Either way, avoid contact with skin and eyes, as you would with any garden chemicals.
Lime sulphur is quite an old invention and is possibly the earliest synthetic chemical used as a pesticide. It was originally developed by Grison, the head gardener at the vegetable houses in Versailles, France in 1851 to protect plants against mildews. As such, it was originally known as “Grison Liquid” or “Eau Grison”. The first use of lime sulphur for the control of peach leaf curl was in California in 1886.
How it works
Lime sulphur is an eradicant which acts by killing fungi on contact. It breaks down after it’s applied, releasing sulphur. The sulphur is the only part that’s toxic to fungi, and it eradicates them through direct contact or through fumigation by sulphur vapours, which can work from a distance.
To explain in simple terms how sulphur works with fungi, they absorb it and it interferes with their ability to create energy, it also turns into hydrogen sulphide (commonly known as “rotten egg gas”) which poisons them.
In more technical terms, sulphur has two modes of action, impaired electron transport and hydrogen sulphide (H2S) formation. Sulphur disrupts the transfer of electrons in the cytochrome system respiratory chain of fungi, depriving the cell of energy, and causing the reduction of sulphur to hydrogen sulphide (H2S), which is toxic to most cellular proteins, killing the cell.
Lime sulphur generally prevents plant disease by allowing sulphur to penetrate leaf tissues and kill germinated spores. It is toxic to insects and mites due to hydrogen sulphide formed through reaction of the polysulfide components of lime sulphur with water and carbon dioxide, or put more simply, lime sulphur reacts with the atmosphere to produce hydrogen sulphide (“rotten egg gas”) which poisons the pests.
Pests and diseases controlled with lime sulphur
Lime sulphur can be used to control a range of fungal diseases including Black Spot, Powdery Mildew, Freckle, Leaf Curl, Rust, Shot Hole and Brown Rot, as well as various Scale and Mite pests.
How to use lime sulphur
Lime sulphur is primarily used when plants are dormant but can also be used as a growing season spray.
Dormant season applications are applied late winter, after frosts have passed and before leaves are present.
Growing season applications can be made when leaves are present but should be applied early morning or late afternoon to avoid leaf burn.
To avoid plant damage caused by lime-sulphur, DO NOT spray when:
- temperatures exceed 32°C
- when soil is dry and plants are suffering from moisture stress.
- when freezing weather is expected.
- within 14 days of an oil spray.
When spraying, avoid contaminating waterways and fishponds, do not allow spray to drift onto aquatic environments. Keep children, pets, wildlife and birds off treated areas until the spray is dry.
Lime Sulphur can be used to controls a range of fungal diseases and pests on apples, pears, stone fruit, citrus, grapes, tomatoes, roses & ornamentals.
There is no withholding period, it’s a low toxicity product, so produce can be harvested as required.
It’s an ideal winter clean up spray – spray in winter for prebloom powdery mildew control on apples, leaf curl control on peaches and nectarines, and control of scale on stone fruit trees. Spray roses after pruning to control powdery mildew and mites.
When to spray
The best times to spray different crops as usually listed on the label, timing depends on the crop and the pest or disease. As a quick guide:
Stone Fruit such as almonds, apricots, nectarines, peaches, plums are sprayed while trees are dormant, prior to bud swell. It’s too late to spray once flowering occurs.
Pome Fruit such as apples are sprayed during dormancy to late bud swell.
With apples, there are a few precautions to be aware of. Lime sulphur used after late green tip will restrict growth and depress yield.
- Do not use lime sulphur on Delicious or Cox’s Orange Pippin apples.
- Lime Sulphur used after late green tip stage (period of bud movement when the buds show green tips from the emerging leaves) will restrict growth and depress yield.
Grape Vines are sprayed as near as possible to bud burst.
Roses and many other ornamentals can be sprayed during dormancy as a winter spray, or during the growing season from spring to autumn, make sure to wet the leaves and repeat as required.
Tomatoes and other vegetables can be sprayed during the growing season from spring to autumn, make sure to wet the leaves and repeat as required.
Sulphur sensitive plants
Some plants are sensitive to sulphur and should NOT be sprayed during the growing period when they are in leaf – these include apricots, raspberries, cucurbits, and peaches. Check if plants are sulphur sensitive before spraying during the growing period.
Lime sulphur or copper fungicides?
Lime sulphur is both an insecticide and a fungicide, whereas copper fungicides are just that. Another important consideration is that copper is toxic to plants when there’s a lot of it in the soil, and it doesn’t break down at all. Repeated seasonal spraying with copper-based fungicides aren’t the best for the soil. Never apply copper to strawberries, because severe phytotoxicity (plant toxicity) will result under almost any conditions. Use copper fungicides when the use of lime-sulphur is not advised (and the use of copper fungicide is!), and in those cases, use just enough spray to wet the plant surfaces without runoff.
As a handy tip,, some organic gardeners prevent runoff or spray drift by placing newspaper or plastic sheet under the tree being spayed with copper fungicide to prevent it getting into the soil.
- Lime-sulfur: A fungicide used to control a variety of diseases by Don Janssen, Extension Educator, University of Nebraska–Lincoln, Nebraska Extension in Lancaster County – https://lancaster.unl.edu/hort/articles/2002/lime-sulfur.shtml
- 2018 Crop Protection Guide for Tree Fruits in Washington, Fruit and Leaf Injury, Washington State University – http://www.tfrec.wsu.edu/pages/cpg/Leaf_Injury
- University of Maryland Extension, Home and Garden Information Center, Fruit – Fungicides – https://extension.umd.edu/hgic/fruit-fungicides
- Rural Industries Research and Development Corporation – Growing Organic Apples – World class production systems for new Australian apple varieties