BLIGHT, in agriculture, a general name for various distempers incident to corn and fruit trees. It affects them va riously, the whole plant sometimes pe rishing by it, and sometimes only the leaves and blossoms, which will be scorch ed and shrivelled up, the rest remaining green and flourishing. Some have sup posed that blights are produced by east. erly winds, which bring vast quantities of insects' eggs along with them from dis tant places. These, being lodged upon the surface of the leaves and flowers of fruit-trees, cause them to shrivel up and perish. Mr. Knight, however, observes, that ',lights are produced by a variety of causes, by insects, by an excess of heat or cold, of drought or moisture ; for these necessarily derange and destroy the deli cate organization of the blossoms.
The term blight is very frequently used by the gardener and farmer without any definite idea being annexed to it. If the leaves of their trees be eaten by the caterpillar, or contracted by the aphis; if the blossoms fall from the ravages of insects, or without any apparent cause ; the trees are equally blighted ; and if an east wind happen to have blown, the in sects, or at least their eggs, whatever be their size, are supposed to have been brought by it. The true cause of blight seems to be, continued dry easterly winds for several days together, without the in tervention of showers or any morning dew, by which the perspiration in the tender blossoms is stopped : and if it so happen that there is a long continuance of the same weather, it equally affects the tender leaves, whereby their colour is changed, and they wither and decay.
The best remedy, perhaps, is gently to wash and sprinkle over the tree, &c. from time to time, with common water ; and if the young shoots seem to be much infect. 'ed, let them be washed with a woollen cloth, so as to clear them, if possible, from this glutinous matter, that their re spiration and perspiration may not he ob structed. This operation ought to be performed early in the clay, that the moisture may be exhaled before the cold of the night comes on ; nor should it be done when the sun shines very hot.
Another cause of blights in the spring is said to be sharp hoary frosts, which are often succeeded by hot sun-shine in the day-time. This is the most sudden and certain destroyer of fruit that is known. The chief remedy to be de pended upon in this case is, that of pro tecting the fruit trees during the night time with nets. This mode, where regu larly and correctly performed, has been found highly beneficial.
What is termed the blight is frequent ly, however, no more than a debility or distemper in trees. Mr. Forsyth observes,
that "this is the case when trees against the same wall, and enjoying the same ad vantages in every respect, differ greatly in their health and vigour, the weak ones appearing to be continually blighted, while the others remain in a flourishing condition. This very great difference, in such circumstances, can be attributed only to the different constitutions of the trees, proceeding from want of proper nourishment, or from some bad qualities in the soil ; some distemper in the stock, buds, or scions ; or from some misma nagement in the pruning, &c. all of which are productive of distempers in trees, of which they are, with difficulty, cured. If the fault be in the soil, it must," he says, "be dug out, and fresh mould put in its place ; or, the trees must be taken up, and others, better adapted to the soil, planted in their room. It will be found absolutely necessary always to endeavour to suit the particular sorts of fruit to the nature of the soil ; for it is in vain to ex pect all sorts of fruit to be good in the same soil. If the weakness of the tree proceed from an in-bred distemper, it will be advisable to remove it at once, and after renewing the earth to plant ano ther in its place." But if the weakness is brought on by ill management in the pruning, which is frequently the case, he would advise more attention to the me thod of pruning and training. Besides this, "there is another sort of blight that sometimes happens pretty late in the spring, as in April or May, which is very destructive to fruit trees in orchards and open plantations, and against which we know of no effectual remedy. This is what is called a fire-blast, which, in a few hours, hath not only destroyed the fruit and leaves, but often parts of trees ; and sometimes entire trees have been killed by it. As this generally happens in close plantations, where the vapours from the earth and the perspiration from the trees are pent in, for want of a free circu lation of air to disperse them, it points out to us the only way yet known of guarding against this enemy to fruits ; namely, to make choice of a clear healthy situation for kitchen-gardens, orchards, &c. And to plant the trees at such a dis tance as to give free admission to the air, that it may dispel those vapours before they are formed into such volumes as to occasion these blasts." But blasts may also be occasioned by the reflection of the sun's rays from hollow clouds, which sometimes act as burning mirrors, and oc casion excessive heat. See APIIIS.