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petroleum fractions as natural components, or they may be made toxic by the addition <br /> of oil-soluble additives. Commercial weed oils are special refinery fractions which <br /> contain higher proportions of petroleum toxicants than are normally present in oils <br /> refined for use as fuel. Little is to be gained by the addition of chemical toxicants to <br /> commercial brands of weed oils. <br /> In petroleum oils, plant toxicity is largely associated with the un-saturated and, more <br /> particularly, the aromatic fractions. The content of aromatic compounds in an oil is an <br /> excellent index of its efficiency as a weed killer, and the specifications of commercial <br /> weed oils usually state the percent of aromatics in the formulation. Diesel oils and other <br /> fuels deficient in aromatics can be made as toxic as desired by fortifying with such <br /> materials as oil-soluble dinitro (dinitro general herbicide) and pentachlorophenol. <br /> For maximum economy, oils should be sufficiently toxic to be effective when applied to <br /> weed growth as a very light film. Drenching sprays should not be necessary, although <br /> heavier applications are required on perennial grasses, such as johnsongrass and <br /> bermudagrass. <br /> High toxic oils are usually effective at lower rates than they can conveniently be applied <br /> and may be better utilized by application as emulsions with water. The additional <br /> volume gained by emulsifying with water permits better visual control of application, and <br /> the larger droplet size of spray reduces drift and provides driving force to carry the spray <br /> into dense vegetation. <br /> Emulsions are made by adding a small amount of emulsifying agent to the oil and <br /> mixing it with one to three volumes of water in a spray rig equipped with an agitator. <br /> Some weed oils have the emulsifier added by the supplier, or have an effective <br /> emulsifying agent as a natural component of the oil. If agitation in the spray tank is <br /> sufficiently vigorous, emulsifying agents are not needed. <br /> It is important to remember that the sole purpose of emulsifying weed oil with water is to <br /> aid distribution. Nothing is to be gained by making emulsions of oils of moderate and <br /> low toxicity, as they already have enough volume to spread their toxic action to the <br /> maximum. <br /> Growers who use small quantities of weed oil often find it more convenient to use diesel <br /> fuel or orchard heater fuel as a herbicide. It is usually advantageous to increase the <br /> toxicity of these oils by fortifying with dinitro general or pentachlorophenol As the <br /> amount of fortifying agent added to.the oil is increased, the resulting concentrates may <br /> be emulsified with increasing amounts of water and the saving in cost of oil used, up to <br /> a point, will more than compensate for the cost of the fortifying material. Although <br /> fortified oil emulsions containing as little as 5 percent oil may be used successfully to <br /> control young weeds provided sufficient fortifier is added, mixed annual and perennial <br /> growth is best controlled with emulsions containing upwards of 30 percent oil. <br /> Translocated herbicides, so-called because they are absorbed by the foliage and <br /> translocated within the plant, can be used in controlling wild morning glory and certain <br /> other broadleaved perennials, Examples of this type of herbicide are 2, 4-D, 2, 4, 5-T <br /> and amino triazole. In using 2, 4-D and 2, 4, 5-T, precautions should be taken to avoid <br /> drift which could cause serious damage to avocado trees. Low-volatile esters of 2, 4-D <br />