FUNGICIDES, fun'ji-sid, any agent used to prevent the growth of fungi or their spores. The most important uses of fungicides are in agriculture and horticulture for controlling the fungi that attack crops. These may be divided into two general classes: (1) Fungi which burrow among the tissues of the host plants and expose little more than their fruiting organs to the air. (2) Fungi which expose almost all of their vegetative parts to the air, only the holdfast, absorbing organs (haustoria) entering the tissues of the host. From the nature of their growth it is easily seen that members of the second group may be attacked at any time, but that since the vegetative parts of members of the first group are protected by the tissues of the host they cannot be reached effectively by any fungicide without injuring the host. Controlling agencies in such cases must therefore be preventive. • For the control of the exposed fungi the chief agent is sulphur in out-door practice, ap plied as a powder, which is dusted upon the foliage, preferably with a powder gun. In the greenhouse it is more frequently evaporated, by strewing powdered sulphur upon the heating pipes or upon burlap suspended in warm parts of the greenhouse. This is a slow way, and is mainly preventive. When a considerable quan tity must be evaporated in a short time the sulphur is gently heated over an oil stove. It is imperative that the sulphur be kept from igniting, because the fumes are destructive to host as well as fungus. For cleansing a green house of objectionable fungi when the plants are out, the sulphur may be burned and all reachable parts sprayed liberally with Bordeaux mixture.
Various compounds of copper are used as preventives of the attacks of internal feeding fungi and as remedies for the exposed. Chief of these salts is copper sulphate, which may be applied in a pure solution only to dormant wood, walls, etc. It is used at the rate of one pound to the gallon, and will, at this strength, destroy lichens and algae as well as fungi. For use upon foliage and other actively growing parts it must be mixed with some substance which will counteract its causticity. Lime is most frequently used, and the compound is called Bordeaux mixture from the French city where its usefulness was accidentally dis covered about 1882. It is made as follows:
A known number of pounds of copper sulphate are dissolved in an equal number of gallons of water, contained in a wooden tank or barrel, the salt being suspended at the surface of the water to ensure quick solution. In another receptacle a known number of pounds of lime, as free from magnesium as possible, are slaked with a little water, and when slaking is com plete, enough more water is added to make the proportion one pound of lime to a gallon of water. When needed for use five gallons of the copper sulphate solution and five of the lime solution are separately diluted with enough water to make a combined total of 50 gallons.
The two diluted solutions are then thoroughly mixed, and afterward tested with ferrocyanide of potash to make sure that there is no un combined copper sulphate. A brownish dis coloration indicates that more lime must be added to neutralize the free copper salt. The mixture is then ready for general use, but for peaches, plums, cherries and some other plants, another 25 gallons of water must be added be cause of the susceptibility of the foliage to in jury. The stock solution of copper may be kept for weeks, but the lime solution should stand for only a few days and the completed mixture for only a few hours, because the particles tend to flocculate and settle, a process which impairs the usefulness of the mixture.
Copper sulphate is often used as eau celeste, a solution of one pound of the salt to two gal lons of water, plus three half-pints of standard ammonia, and then diluted with water to make 25 gallons. Since the strength of the ammonia varies, this solution often burns the foliage, there being insufficient ammonia to neutralize the free copper sulphate. This fungicide and ammoniacal solution of copper carbonate are used when a non-staining solution is needed, as in spraying ornamental plants and fruit which is nearing maturity. The latter solution is made by dissolving one ounce of copper car bonate in one pint of ammonia and mixing with 10 gallons of water.