Repository: UIHistories Project: Board of Trustees Minutes - 1880 [PAGE 158]

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The Red Cedar is preyed upon by quite a different fungus (Gymnosporangia macropus), whose" fruit in springtime has the appearance of yellow balls with jelly-like sprangling arms over the whole surface. The foregoing of the Peach parasite shows that the mode of living is similar to that of the Cedar fungus, whose life history has long been known and which may be exterminated by proper pruning.

BLACK BUST OF VERBENAS.

Florists have suffered great losses and more annoyance from a disease of Verbenas called the Black Bast to distinguish the malady from that called Mildew, which is white. Notwithstanding the difference in the names and the greater difference in the appearance of the two diseases, they have been confounded with each other in published accounts and proposed remedies. Even specialists to whom specimens have been sent, have returned accounts which clearly show the two diseases were not distinguished. This mildew on the leaves of cultivated Verbenas was some years ago determined by myself to be Erysiphe Communis, a fungus found on many plants. The black rust is now determined to be caused by a mite, a small spider-like thing, invisible to the naked eye. Others have heretofore announced this as a theory, and have no doubt seen the mites; but nothing conclusive has been published, and florists do not yet know the foe that they are vainly trying to fight. The mite itself has never been described, a figure given by an author on floriculture not being accurate enough to show that the real depredator had been seen at all. Other mites are frequently found running over leaves of every kind, and some of these may have been taken for the much smaller one, which causes the difficulty. Affected plants, especially the younger portions of them, have a dark, purplish color; they grow slowly, look sickly and scarcely flower at all. An entirely new observation is that these plants in beds out of doors are likewise injured, and that the mite lives throughout the summer and until the ground freezes in autumn on them. In these situations the purplish color is not so much confined to the buds, young stems and small leaves; the whole plant is more or less tinged, and the mites are likewise found on the older parts. After a time the older leaves have a whitish, scaly and ragged appearance, finally becoming hard and dry. Such plants bloom little—are in fact worthless, The mite is a very peculiar one, belonging almost surely to an undescribed genus of the family Tyroglipidw, which includes the common cheese mite. It probably passes its whole existence upon the leaves, or in winter hibernates in the perfect state under cover of rubbish on the ground. From the beds out of doors it is transferred to the greenhouses with the plants or cuttings. This last fact, together with the truth that the disease is caused by an insect-like parasite, suggests the following proposed remedy: 1st, select plants in autumn free from mites, as indicated by their fresh and green appearance; or, if this can not be done, dip the plants in water at a temperature of 120° Fahrenheit two or three times at intervals of a day or two. 2d, syringe the affected plants with a half pint of coal oil in three gallons of water, taking care to mix the two by forcing the water from the syringe into the vessel and immediately refilling from the agitated liquid. The application must be made with force, so as to reach all parts of the plants.

THE PEAR-LEAF BLISTER.

We give this name to a peculiar disease of pear leaves first traced to its origin by a German naturalist twenty-one years ago. Though widely disseminated in our country, no mention has heretofore been made, except by the writer, of its identity with the European malady, and no one else has to my knowledge pointed out the cause of the disease as it occurs with us. I am able, also, to add an important item in the life history of the mite-parasite (for such it is), not previously published. In spring-time.the young leaves are spotted with red and are slightly distorted. Sometimes the spots are few and scattered, sometimes very numerous and conspicuous. At a later time the spots become brown by the death of the tissues. Upon very close inspection with a good hand magnifier, a minute hole can be seen in the center of the spot on the underside of the leaf. Dissecting the affected portion of the leaf and using the compound microscope with a power of a hundred diameters, numerous flesh-colored mites can be seen which slowly and clumsily drag themselves about by four legs which project forward. Scheuten, the German naturalist referred to, called the mite Typhlodromus pyri, but there does not appear any good reason for separating this from other similar mites belonging to the genus Phytoplus, hence the proper name for this is no doubt Phytoplus pyri. Scheuten and others have supposed the form seen was the young of other forms someiimes found associated with them, but this is abundantly refuted, especially by the observation of the insect in its egg-producing and winter state. The new contribution alluded to is the discovery that in autumn oefore the leaves fall, the most of the mites creep out of the leaf-galls down the leaf-stalk and pass the winter between the scales of the buds. They may be found in this situation now, (December 17,1878,) and after keeping them in a warm room may be seen crawling about as in summer. The proposed remedy is to prune and burn affected limbs as fast as observed. In this way the tree may soon be freed from the minute enemy. They are so sluggish and clumsy in their movements that the journey down the leaf stock must be a great one for them, not to speak of creeping from tree to tree. Still it is possible that occasional distribution takes place through some of the mites remaining in the leaves until they fall and are blown about by the winds. The more obvious method of dissemination over the whole country is by the use of affected buds by nurserymen. The mites have doubtless come to America in this manner from Europe, and have since spread with the trees. There is no more question about the destruction of this mite than of its relative, which chooses the human skin for its habitation,—the itch mite. Neither originate spontaneously: they are produced from eggs laid by parent mites. A tree once cleared remains so until the pest is again introduced.