Fungicide

“ The tools should be thoroughly sterilized by immersion in a solution of 1.1000 bichloride of mercury, or 5 per cent solution of formaldehyde, before cutting into the bark outside of the diseased area. Experiments have shown that a gouge or knife may carry the spores into healthy bark and new infection take place. Experiments are being carried on in the laboratory to determine the length of time which spores will live in solutions of different strengths of fungicides. ”

“ The same substance is sometimes much more injurious to the tissues of one part of a plant than it is to those of another part of the same plant. Thus, the rootlets of a young growing plant are much more susceptible to injury by many mineral salts than are the vegetative parts of the same plants; while anæsthetics of various kinds generally exhibit their greatest injurious effects upon the leaves, or synthetizing cells. Again, the mycelia of fungi are much more easily killed by toxic agents used as fungicides than are the spores of the same fungi. ”

“ Control.—The control of pecan scab disease depends primarily on the protection of tender leaf, nut and shoot surfaces with proper application of an effective fungicide. A protective film of fungicide chemical prevents scab fungus infections by killing the spores immediately after their germination, thereby preventing invasion of susceptible tissues. Unfortunately, once the fungus has invaded the tissues it becomes protected from chemical attack and produces spores in great abundance. ”

“ With tracers it is possible for the first time to measure chemical uptake in single spores and to follow chemicals through the plant. Perhaps the most enlightening information from such studies is that some fungicides are 10,000 times less effective per unit of “body weight” than are other chemicals used to destroy weeds and insects. Obviously the breakthrough in chemical control of plant diseases is yet to come.
10 Why Do Chemicals Destroy Some Plants?
Weeds cost this country an estimated $5 billion annually, which is more than the loss to either plant diseases or insects. ”

“ Occasionally, the disease is rather serious, but it is not often to be reckoned with in the vineyard regions of America. Fungicides are useless in combating the disease and all that can be done is to exercise great care in planting infected stock. ”

“ With many of the fungi in the soil the roots of plants have to compete—just as plant competes with plant—for water, salts, and other food-materials. The toadstools which are so conspicuous in fields and forests spring from mycelia which ramify in the ground, and are busily breaking down the remains of other organisms, and just such fungi are known to store up relatively large quantities of salts of potassium and phosphorus—the very salts which are so valuable to crops and occur so sparingly in most soils, but which the extensively spread fungus mycelia can gradually accumulate. ”

“ They may attack leather, cloth, etc., in a damp house. Other allied forms may do damage to living plants. Some of these live upon the lilac, rose, or willow. These fungi do not penetrate the host plant to any depth, for they obtain their food from the outer layer of cells in the leaf of their host and cover the leaves with the whitish threads of the mycelium. Hence they may be killed by means of applications of some fungus-killing fluid, as Bordeaux mixture. ”

“ And before we come to the mushrooms, which you know so well, we must look at the smaller forms, which do all their work above ground, so that we can observe them. For the fungi are to be found almost everywhere. The film growing over manure-heaps, the yeast plant, the wine fungus, and the vinegar plant; the moulds and mildews covering our cellar-walls and cupboards, or growing on decayed leaves and wood, on stale fruit, [Pg 61] bread, or jam, or making black spots on the leaves of the rose, the hop, or the vine; the potato fungus, eating into the potato in the dark ground and producing disease ”

“ It is, also, usually the persons who think they know the mushroom, and can not be deceived, that get poisoned. If two rules are observed danger can be avoided. (1) Never eat a fungus gathered in the woods believing it to be the mushroom. The typical A. campester does not grow in the woods; species of Agaricus somewhat resembling it do. (2) Look at the gills; those of the mushroom are at first a light-pink which rapidly, as the plant matures, darken to a dark-brown, purplish-brown, or purplish-black. This is due to the ripening of the spores. Those of the Amanita are constantly white. ”

“ It any state most plants feed greedily upon it, and when pure or free from decaying wood or sticks it is a very safe ingredient in composts; but it is so liable to generate fungus, and the mycelium or spawn of certain fungi is so injurious to the roots of trees, attacking them if at all sickly or weakened by drought, that many cultivators prefer not to mix leaf-mould with the soil used for permanent plants, as peaches or choice ornamental trees. ”

“ It is as attractive and as poisonous as it is beautiful. In Kamtchatka, it is highly prized for its poisonous properties, producing, as it does, in the eater a peculiar intoxication. The fungus is gathered and dried; and when a native wishes to engage in a debauch, he has but to swallow a piece, when in a few hours he will be in his glory.”— (Johnson’s New Universal Cyclopædia, New York, 1878, article “Mushroom.”)
Poisonous fungi. “Several of this natural order are poisonous, especially those belonging to the genera Amanita and Agaricus.... ”

“ In the penultimate zone the grass is dead, probably not caused by a direct parasitic attack but by the mycelial threads filling the air-spaces in the soil and so inhibiting water flow. This destruction of the delicate balance of water and air found in any soil induces drying out and gradual death of the plants whose roots permeate the soil. Behind the dead-zone is vegetation which shows increased vigour apparently due to plant-nutrients being released by the decaying mycelium and plant-material, whose death has been caused by the presence of the fungus. The innermost zone is not so stimulated. ”

“ A second aspect is the direct encouragement of special components of the fungus flora for particular purposes by selective feeding. Thus, in a laboratory experiment, McBeth and Scales [43] record an increase of 2000 times in cellulose-destroying and other soil fungi by this method. It has been pointed out that soil fungus activities such as ammonification, proteolysis and carbohydrate decomposition are controlled by factorial equilibria, and for special purposes it would seem feasible to weight the balance so that particular activities may be favoured. ”

“ Experiments in these varieties of fungi are highly dangerous, as many of the most poisonous so closely resemble the edible species that they can with difficulty be distinguished. There is one kind of fungus that I have met with in the forests which, from its offensive odor and disgusting appearance, should be something superlatively bad. It grows about four inches high; the top is round, with a fleshy and inflamed appearance; the stalk is out of all proportion in its thickness, being about two inches in diameter and of a livid white color ”

“ Unfertilised eggs of insects have been started into growth by treatment with acids and those of frogs with mercury salts, and the germination of beans quickened by various poisonous alkaloids. In other words, graduated doses of [131] poison may alter the physiological activity of living cells, inducing pathological phenomena, while larger doses kill them.
Now we know at least one parasitic fungus which poisons the cells of its host, and kills them, with similar symptoms to those resulting from excessive doses of the above-named toxic agents. ”

“ The starting-point is a fungus, Marasmius oreades, which in due course sheds its spores in a tiny circle around it; the decay of the fungus supplies nitrogen to the grass, and renders it dark green in colour. The circle expands, always outwards, more and more fungi appearing every year; it does not return inwards because the mineral constituents of the soil are exhausted by the growth of the fungus and of the grass, under the stimulus of the abundant nitrogen left by the former, so that the dark ring of grass extends its diameter year by year. ”

“ Later on, spores of a very different kind are produced. Unlike those already studied, they are formed some distance below the epidermis, and in order to study them satisfactorily, the fungus must be freed from the host plant. In order to do this, small pieces of the leaf should be boiled for about a minute in strong caustic potash, and then treated with acetic or hydrochloric acid. By this means the tissues of the leaf become so soft as to be readily removed, while the fungus is but little affected. The preparation should now be washed and mounted in dilute glycerine. ”

“ Indeed, fungi have an advantage in this respect, since one or two general cautions can be given, when none such are applicable for higher plants. For instance, it may be said truly that all fungi that exhibit a rapid change to blue when bruised or broken should be avoided; that all Agarics are open to suspicion which possess an acrid taste; that fungi found growing on wood should not be eaten unless the species is well known; that no species of edible fungus has a strong, unpleasant odour, and similar cautions, which, after all, are insufficient. ”

“ There is no cargo, even that which is shipped in tolerably dry condition, in which, upon its arriving here, may not be found some deals, with the fungus beginning to vegetate on their surface. If they are deals that have been floated down the rivers of America or Canada, and shipped in a wet state, on their arrival here they are so covered with this network of the fungus, that force is often necessary to separate one deal from another, so strongly does the fungus occasion them to adhere. ”

“ They collect the fungi in the hottest months, and hang them up to dry. The fungus is then rolled up in a kind of bolus, and swallowed without chewing. One large, or two small, fungi will produce a kind of intoxication, which lasts a whole day. It comes on in about two hours’ time, and is very similar to that of alcohol. There is a giddy feeling, the spirits are exalted, the countenance becomes flushed, involuntary actions and words follow, and sometimes loss of consciousness. ”

“ Even the most wholesome mushroom will occasionally require to be discriminated against, as certain individuals find it necessary to exclude cabbage, milk, onions, and other common food from their diet. When we reflect, moreover, that in its essential chemical affinities the fungus simulates animal flesh, and many of the larger and more solid varieties are similarly subject to speedy decomposition, it is obviously important that [Pg 31] all fungi procured for the table should be collected in their prime, and prepared and served as quickly as possible. ”

“ Whatever, therefore, may be the appearance or situation of the fungus producing the dry rot, or from whatever substance it originates, that substance must be in a corrupt state.
Fungi result from, or are attendant on, vegetable corruption, assisted by an adequate proportion of heat and moisture. The sap, or principle of vegetation, brought into activity, is, according to the ‘Quarterly Review,’ No. 15, the cause of dry rot, in as far as it is favourable to the growth of fungi, as it would seem to be when in a state of fermentation.
Vegetable corruption invariably presupposes fermentation. ”

“ That we may better understand the structure of the disease-causing fungi we are about to examine, let us refresh our memories concerning that very common fungus, known as white mould and mentioned in an earlier chapter. The reason fungi cause damage to other plants, the one invariable reason, is that they, being unable to manufacture food for themselves, steal it from the plants on which they grow. Some of them are parasites and steal their food from living animals or plants; others live upon dead animal or vegetable matter and the white mould is one of the latter fungi. ”

“ They mark the area of growth of some fungus, starting from a centre of one or more plants. The mycelium produced from the spores dropped by the fungus or from the “spawn” in the soil, radiates outwards, and each year’s successive crop of fungi rises from the new growth round the circle. The rich colour of the grass is due to the fertilizing quality of the decaying fungi, which are peculiarly rich in nitrogenous substances. ”

“ The fungal growth spreads through the substance to the leaf, robbing the leaf of its nourishment and causing it to wither and fall. An infected plantation may be cleansed, and the fungus in its nascent state destroyed, by powdering the trees with a mixture of lime and sulphur, but, unless the access of fresh spores brought by the wind can be arrested, the plantations may be readily reinfected when the lime and sulphur are washed off by rain. ”

“ It inhabits dry places, especially birchwoods, and pinewoods, having a bright red upper surface studded with brown warts; and when taken as a poisonous agent it causes intoxication, delirium, and death through narcotism. It is more common in Scotland than in England. This Mushroom is highly poisonous, and therefore the remedial preparations are only to be given in a diluted form. For medicinal purposes a tincture is made (H.) from the fresh fungus: and a trituration of the dried fungus powdered and mixed with inert sugar of milk also powdered. ”