Herbicidal properties of oils

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Introduction

Oils as Herbicides. Oils of many types have been employed as herbicides. In the West, petroleum fractions have been most popular; and of these Diesel oil, stove oil, and smudge-pot oil have been applied in greatest volume. They have been used to kill general weed growth on roadsides and railway roadbeds in order to prevent the spread of fires. They are a means of eliminating the vegetation that depletes soil-moisture reserves in citrus groves; of destroying the weeds that harbor insect and fungus pests on ditchbanks, fence rows, and similar untilled areas; and of burning undesirable growth on irrigation ditches. Over 3 million gallons have been consumed annually in California for these purposes, and the use is expanding rapidly. Recently stove oil has been applied as a selective spray against weeds in vegetable crops, notably carrots, celery, and parsley.

The herbicidal use of oils has developed through many years. Early practices utilized acid sludge, acid tar, Edeleanu extracts, and other by-products of oil refining that had little commercial value. In the East, residues from coal and wood distillation, various petroleum fractions, gas oils, and similar low-cost products have been applied to weeds. Availability and hauling cost have largely determined distribution and the extent of use.

Increased demand for oils as motor and heating fuel has been accompanied by improvement in the quality of these products; herbicidal toxicity has likewise been altered. Unsaturated compounds, particularly the aromatics, tend to make fuel oils burn sooty, and they have antiknock properties that are undesirable in a Diesel fuel. These compounds are toxic to plants, and their removal decreases the killing action of an oil. One problem is that of providing enough toxicity per unit volume to kill plants with the amount required to wet them.