The mildew occurs most frequently on wheat, hops, the dead nettle, maple, and the gromwell. It sometimes rests on vegetables in the form of a fatty juice ; which, being naturally tough and viscous, acquires these properties in a still greater degree, in consequence of its finer and more fluid parts being exhaled by the sun ; so that the plants affected, by it, cannot perform the important office of perspiration, and thus never at-tain to maturity.
According to Dr. Darwin, the mildew is a plant of the fungus kind, which vegetates without light or change or air, in the same manner as the generality of mushrooms ; and penetrates with roots the vessels to which it adheres. He suspects, however, the plants affected, to have been previously injured by internal disease; and directs them to be thinned; or to remove those which are contiguous to the diseased, in order to admit more light, and greater ventilation : thus the mildew may be remedied, and the plant at the, same time restored to its former vigour.
Common wheat is more subject to this destructive disease than that which is bearded, especially if the land be newly dunged. As, however, it is highly probable, that the greater dampness of some soils, together with their being over-shadowed by too thick foliage, affords one permanent cause of mildew, Dr. Darwin recommends the land to be properly drained; the ashes of coals, bones, or other drier manures,to be employed ; and likewise to thin the crops. And, as this mucor particularly affects late crops, he is farther of opinion, that the seed should be sown early in the season; by which means the mildew will not only be prevented, but a forward crop will be obtained.
Where this disease has already infested the plants, a brisk shower of rain, succeeded by a smart wind, is believed to be the most efficacious remedy, to prevent its farther progress. If the mildew be observed before the sun rises to its meridian power, it will be advisable to send two men into the field, furnished with a long cord, of which each should hold one end : by dexterously drawing this rope over the ears of corn, the dew will be removed, before the heat of the sun dries and reduces it to that viscous state, in which it obstructs the perspiration of plants. Lastly, it has been confidently asserted, that lands, which have been affected with the mildew for several successive years, have been effectually cured by sowing soot, either together with, or immediately after corn; and that hop-plantations may be secured from its injurious effects, by manuring them with hogs'-dung.
M. Seger, in his valuable Ger-man Treatise on the Mildew, considered as the principal cause of Epidemic Diseases among Cattle, etc. (published at Vienna in J 770), observes, that the mildew is so sharp and corrosive, as to raise blisters on the feet of shepherds who go with naked feet; and that it even consumes the hoofs of cattle. He supposes it to be a kind of rust, and to possess some arsenical properties. Its pernicious influence is rendered still more powerful by a variety of circumstances ; such, as sending cattle into tie fields too early in the spring ; suffering them to drink water mixed with ice ; or keeping them in close, filthy stables, that are not sufficiently aired.
M. Seger likewise conceives the mildew to be a principal cause of epidemical diseases in cattle. The particular species, producing such distempers, is that which burns the grass and leaves. It falls usually in the morning, especially after a thunder-storm; and its poisonous properties (which do not continue above twenty-lour hours) never operate, unless the mildew be swallowed immediately after it has fallen.—The disease first affects the stomach, and is accompanied with pimples on the tongue, loss of appetite, a cough, and great difficulty of respiration. As a preservative, the ingenious author directs cattle to be well purged, both in the spring and in winter ; for which purpose he prescribes half a dram of sulphur of antimony, and a whole dram of resin of jalap, for one dose :—he concludes with cautioning the proprietors of cattle, carefully to avoid the use of emetics, and every thing that is of a heating or irritating nature; because such treatment would be productive of fatal consequences.
Mildew, a distemper which, from its clammy nature, is equally injurious to trees and plants, by closing up their pores, so that their perspiration is obstructed, and their growth is checked. - Contrary to the commonly received opinion, Mr. Forsyth has observed, that fruit-trees are more liable to this malady, when planted against South and West walls, than those exposed to the East ; and, by removing such diseased trees to North or East walls, they have perfectly recovered.
Where danger is apprehended from the mildew, Mr. F. advises the trees to be sprinkled with urine and lime-water; but, if the young shoots be much infected, it will be necessary to wash them with a woollen cloth, dipped in the mixture, which has been specified in the article Blight (p. 399, of this Supplement), with a view to clear them of all glutinous or viscid matters ; so that their exhalation may not be impeded.