Insect and Mite Control on Woody Ornamentals and Herbaceous Perennials

Bulletin 504

Alternative Products
Their Selection and Use for Insect and Mite Control on Ornamentals

Introduction

In the previous chapter, we discussed the Integrated Pest Management process and the control options available. Recent interest in alternatives to traditional synthetic pesticides has resulted in numerous products containing botanicals, oils, soaps and microbial materials.

These alternative products often do not act in the same manner as traditional pesticides and the user must understand when these products can be used effectively and what special conditions must be met in order to be successful.

Oils

Oils are petroleum or plant based hydrocarbon chains which have insecticidal/miticidal activity.

The use of oil to kill insects and mites has been known to work since the 1700s. However, the early use of oil usually resulted in killing the plants as well as the insects. Oil came into widespread use to control insects and mites after oil refining techniques were developed which would free the petroleum oils of unsaturated hydrocarbons, acids, and highly volatile elements. Oil is effective against insects and mites because it suffocates or causes cell membrane destruction of the pests that it hits as well as their eggs. Another advantage of oil is that no pest has been known to become resistant to its killing action.

At least three different types of oil are used for pest control: petroleum, summer or horticultural oil, petroleum dormant oil and citrus oil.

Petroleum summer or horticultural oil is a lighter weight oil applied during the active growth of a plant, when green plant foliage is present.

The dormant oil is usually defined as a heavier weight oil applied in spring prior to bud break or in the fall after leaf drop.

Citrus oil is usually added to other pesticide formulations such as soaps and botanical pesticides.

What makes the identification of oils confusing is the fact that summer oils can be used as dormant oils. However, do not use a dormant oil as a summer oil. The simplest method for identifying oils is to READ THE LABEL. If the label only mentions usage on dormant plants, it is a dormant oil. On the other hand, if the label mentions using the oil on green, leafy plants during the growing season, it is a summer oil.

If you don't want to rely only on the label instructions, there are three oil factor which you need to evaluate: 1. oil volatility, 2. oil viscosity, and 3. the unsulfonated residue rating.

Volatility is measured by the distillation temperature. This is the temperature that the oil comes out of heated crude oil at the refinery. A low distillation temperature produces a light oil. A high distillation temperature produces a heavy oil. The lighter oils evaporate faster and thus have less of a chance to cause plant damage (phytotoxicity). The heavy oils may coat the plant and either smother the leaves or destroy some of the cells. The result is phytotoxicity. The distillation temperature is probably the most important number to look for on the label.

Volatility and Oil Usage
Distillation Temperature	Primary Use	Dosage per 100 Gallons
412°F	Summer	1.5-3 gal.
435°F	Summer/Dormant	1.5-2 gal./Summer 3-4 gal./Dormant
438°F	Dormant	2-4 gal.

Viscosity is the flow rate or thickness of an oil. It is measured by the time it takes a volume of the oil to flow through a small funnel opening. The label may say that the oil is a 60 second or 100 second oil. In the past, a lot of emphasis was placed on getting an 80 second oil or better. We feel that the volatility rating is more important.

The unsulfonated residue (UR) rating is an index of the quantity of oil free from unsaturated hydrocarbons. Look for oils with a minimum UR of 92%. Some oils are as high as 99% free.

Some of the better oils, especially summer oils, have distillation temperatures of 412°F and UR = 96%.

Even with the best oils, phytotoxicity is always possible. However, this is the same as with standard insecticides! The following guidelines are recommended by most users and manufacturers of dormant and summer oils:

1. Do not apply the oils when the temperature is below 40°F (4.4°C) or above 100°F (37.8°C). If low humidity is accompanying the high temperature, oils have less of a chance of causing damage.
2. Do not apply oils if rain is a possibility or if the plant tissues are wet. The leaves must be dry and the oil must have a chance to evaporate.
3. Avoid spraying or getting drift on oil sensitive plants.
4. Apply the oil according to the label rates. Always go light, not heavy.
5. When using dormant oils or high rates of horticultural oils, do not spray when plant buds are fully open and shoot elongation is occurring.
6. Do not spray plants when the humidity is expected to remain above 90% for 36 to 48 hours.
7. Leaf drop in the fall is not a reliable method for determining plant dormancy. It is better to wait until after several light frosts.
8. Oil sensitive plants are: maples, hickories, black walnut, cryptomera, smoketree and many azaleas.
9. Plants tending towards oil sensitivity are: beech, Japanese holly, redbud, Savin junipers, Photinia, spruces and Douglas-fir.

Most of the oil labels contain a list of plants which are sensitive or tend towards sensitivity. Read them carefully. Most problems occur when oils are simply sprayed on everything in the landscape.

As with all pesticides, use oils only where needed. They do not need to be used as general cover sprays. Plants which have a history aphid, scale and mite problems are the best ones to target.

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