Chapter 11

Insect Pest Management for Organic Crops

Spray Oils

Spray oils have been used as insecticides for centuries and are some of the most effective, safe alternatives to synthetic insecticides and fungicides. Types of oils and oil products that are commercially available and allowed for organic use include petroleum-derived oils (referred to as “narrow-range oils”); summer oils; horticultural oils primarily derived from seeds (e.g., soybean, cottonseed, sesame, neem or other oils); fish oils; and essential oils, such as wintergreen, clove and rosemary are generally pressed from leaves, stems, and/or flowers rather than seeds. Spray oils are commonly used to control scale and mite pests.

Petroleum Oils

Petroleum oils are derived from crude oil, which is separated into fractions by heat in a distillation tower. Different fractions represent different hydrocarbons of various weights, structures and boiling points and each fraction may have different pesticidal properties. The term, “narrow range oils” refers to the fact that these approved spray oils are highly refined and relatively homogeneous. They are allowed for both dormant and growing season uses for insect or disease control. Petroleum derivatives outside the narrow range are prohibited in organic crop production. Approved oil products must not contain any prohibited inert components.

Horticultural Oils

Plant oils are primarily derived from seeds (e.g. soy and canola). Horticultural oils were initially limited to use on plants before buds opened, hence the common term “dormant oil” but later oils were developed for use on green plants, which led to the term “summer oil.”

Fish Oils

Fish oils are very similar in chemical composition to plant oils. They are mostly by-products of the fish processing industry. Fish oil products are often combined with plant oils, and the fish oil is listed as an inert ingredient. Some fish oil products are certified organic.

Essential Oils

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, and/or flowers rather than seeds. They may be formulated with mineral oil in products, which claim to be effective for insect control. Little information is available at present regarding mode of action or efficacy for these products.

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.

Phytotoxicity

Plants appear to have inherent variability in sensitivity to spray oils. Many factors may contribute to phytotoxic effects of oils on plants, which include moisture deficit in leaves, high humidity, high 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.

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