However, unusually dry weather in early summer can reduce the activity of the fungus. Each gypsy moth female can produce up to 800 eggs, thus allowing their populations to grow exponentially within a short period of time. Horticultural oils These products have been available for decades and were originally used by orchardists for insect pests that over-wintered exposed on the trees, such as scale pests. The majority of these products are highly refined petroleum based oils. Now, horticultural oils have become so highly refined that, depending on tank-mix concentrations, they can be applied to trees and shrubs during the dormant and growing seasons, with some limitations.
Oils work primarily by covering and suffocating the pest organism.
In some cases, they can disrupt certain membranes of the exoskeleton. The target pest must be present and exposed at the time of application and the oil must cover the pest in order to be effective. Therefore, oils work best on pests such as scale insects, spider mites, certain adelgids, and others with limited mobility. One attractive feature of oils is that they can kill all life stages, including eggs. Many other pesticide products only kill the immatures and adults.