Dormant Oil is used to kill insects and their eggs by coating tem with the oil so that they smother. Even eggs must breathe by exchanging gases through their shells and a coating of oil interferes with this process and kills the egg. Tent caterpillar eggs are just one of the many kinds of insect eggs living on plants during the winter. The egg stage is the most common over wintering form because it is fairly resistant to cold temperatures.
Dormant oil is heavier weight oil as opposed to summer oil. It is applied during the dormant season that is prior to bud break in spring and after leaf drop in fall. Summer oil is of lighter weight and can be applied to plants are in active growth and in full leaf.
Oils are used mostly to control sucking type pests or soft bodied insects including aphids, scale insects, mealybugs, psyllids and mites.
Dormant oil is mixed with water prior to application. Oils contain emulsifiers which permit the oil to be mixed with water. Oils must be applied while the target organism is present. Oil has no residual effect. Apply when temperatures are higher than 40 degrees F. Do not apply just before rainfall or while leaves are wet. You really need a 48 hour window for applying the dormant oil. Do no apply dormant oils when buds are fully open nor when shoots are actively elongating.
Oil sensitive plants include: beech, black walnut, maples, smoketree, and azaleas.
Lime sulphur is a fungicide spray composed of inorganic sulphur and lime. It is commonly used today to control a variety of diseases such as plum pockets, black knot, black spot of rose and number of raspberry diseases.
Lime sulphur can be applied as a dormant season fungicide or as a growing season spray. Apply the sulphur in late winter or early spring with temperatures above freezing and before leaves are present on the plant. If lime sulphur is used in the growing season, apply in early morning or late afternoon to avoid burning. Plant damage caused by lime sulphur is most severe during dry weather when temperatures reach 80 degrees.
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