|VANCOUVER ISLAND BONSAI CLUB|
by Mark Paterson (edited 2011)
Contents: 1. How to use lime sulphur as a pesticide. 2. What is lime sulphur. 3. History of lime sulphur. 4. Bonsai and lime sulphur. 5. Safety.
1. How to use Lime Sulphur as a pesticide
Please mix the ingredients according to package directions. Spray your tree(s) with enough of the mixture to ensure good coverage (including underside of needles and leaves, without creating excessive runoff. The pot and soil surface should be covered to prevent the mixture from saturating the soil (where lime sulphur would likely have deleterious effects on beneficial micorrhyzal fungus growing in close association with the roots)
Dormant oil should not be used on Beech, Butternut, Colorado Blue Spruce, Cryptomeria, Junipers, Cedars, Spruce - especially Dwarf Alberta Spruce, Douglas Fir, Hickory, Holly, Maples, Walnuts, Redbud, Cotinus and the Delicious variety of apple.
A lime sulphur mixture can protect trees from a variety of pests including apple and pear scab, powdery mildew, rust mites, brown rot, black knot, certain mites, leaf spot, certain blights, scale insects, aphids, and ants. The pathogenic action of lime sulphur is through direct contact or fumigation by sulphur vapors.
Lime Sulphur should not be used on sulphur sensitive plants like blackcurrant, grape, lemon, currants, apricots and cranberry
Users of sulphur and sulphur-based pesticides should remember that sulphur is lethal to many beneficial insects as well as spiders and beneficial mites.
Also - lime sulphur may cause phytotoxicity in plants. This can range from yellowing to leaf drop. It is caused when Lime sulphur is applied to leaves, and when lime sulphur is mixed with other chemicals and oils than those specified as safe. The lime component moderates the phytotoxic effect of the sulphur. Usually the mixture is used in late winter/ early spring when temperatures are above freezing and before the tree leafs out. Lime sulphur can be used in the growing season (i.e., leaves present) if applied early in the morning or late afternoon - not in direct sun. Scorching effects are greater in hot weather or arid conditions.
2. What is lime sulphur?
Sulphur is an effective fungicide/insecticide. The pests absorb the sulphur, resulting in the sulphur being converted to hydrogen sulfide - which then disrupts electron transfer. Sulphur inhibits fungal spore germination.
Hydrated lime is highly alkaline (11.5) and corrosive in effect. It dissolves the binding agents of protein bundles, allowing it to penetrate insect - and human - tissues readily. It is effective against hard to kill insects like scale insects.
3. A little history
Lime sulphur and copper sulphur were the choices of grape farmers to control grapevine powdery mildew in France. It was used in the Americas by 1885 to control San Jose scale. By the 1920’s, the product was in common use. By the 1940’s, synthetic pesticide use was on the rise and replaced many of the uses of lime sulphur.
So far as I can tell, synthetic pesticides are better only in that they can be used on plants with foliage without as much risk of the phytotoxic effects. They are not necessarily more effective as pesticides, nor better for the environment.
4. Lime sulphur and bonsai
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