Chapter 12

Insect Pest Management for Organic Crops

Spray Oils for Controlling Insect Pests

Spray oils include certain fractions of petroleum oils (narrow-range oils), which are considered synthetic and allowed for insect pest control. “Narrow-range oils” are defined as petroleum derivatives—predominately of paraffinic and napthenic fractions. Narrow-range oils are allowed for both dormant and growing season uses for insect control. Allowed oils can also be derived from plant and fish sources. Plant oils are primarily derived from seeds (e.g., soybean, cottonseed, sesame, and canola), while fish oils are by-products of the fish processing industry. Approved products may not contain any prohibited inert components. Another category of products currently available includes mixtures of essential plant oils, such as wintergreen, clove, and rosemary. These are generally pressed from leaves, stems, or flowers, rather than seeds, and then separated by distillation. They may be formulated with mineral oil in products labeled for disease control. Oils have a long history of effective use on fruit trees, but they have not been used as extensively in vegetables and other crops.

Mode of Action

Oils are widely used to control the egg stage of various mites and insects by preventing the normal exchange of gases through the egg surface or interfering with the egg structure. When used against other stages of insects and mites, oils can block the respiratory system, causing suffocation or breakdown of the outside tissue (cuticle) of the insect or mite.

Types of Insect Pests Controlled

Spray oils are most effective against soft-bodied arthropods. They are most commonly used against mites, aphids, whiteflies, thrips, mealybugs, and scale insects. Oil sprays are also used against over-wintering eggs and scales. Because oils lack residual activity, they do not provide control of insects moving into a treated area.

Application

Plants appear to have inherent variability in sensitivity to spray oils. Many factors may contribute to phytotoxic (harmful to plant tissues) effects of oils on plants, which include moisture deficit in leaves, high humidity and temperature, treating very young foliage, and genetic variability in the plants. Avoid spraying oil when temperatures and humidity are high or when plants are under drought or other stress. During warm weather, irrigate plants before spraying and spray in the early morning or on cloudy days when it is cooler.

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