The Rose Rust
(Uredo or Lecythea Rosae) and the Rose Brand (Phragmidium mucronatum) are believed to be forms of a single species of Fungus, the Uredo being the summer form of spore, and the Phragmidium the autumn form, or teleutospore. Both forms occur scattered in small masses on the lower surface of the leaves; indeed, they grow on the same patches of mycelium; but the Brand appears later in the season. The Rust consists of pale yellow, one-celled, round or oval bodies, covered with very fine, prickly warts. The Brand is made up of very different spores, since each is formed of a row of from four to nine cells, which have a brown, warty outer coast. Each spore is borne on a long stalk, thickened below; and each ends, at the tip, in a long, conical, colourless papilla or outgrowth. This Fungus is seldom dangerous to Roses; but it renders the leaves unsightly. Unfortunately, no cure is known; hence, it is advisable to remove and to burn such leaves as show traces of the Fungus, to prevent it from spreading to healthy plants. See Phragmidium. Another Fungus that, at times, renders the leaves of Roses unsightly, is that known as Asteroma Rosae, Lib. (Actinonema Rosae, Fr.), which forms dark purplish-brown spots, with the appearance of fibres radiating from the centre of each. In the spots lie scattered, dark pycnidia, containing two-celled spores. This Fungus is probably only an immature condition of some unknown pyrenomycetous Fungus. To prevent any extension of the slight harm done by it, remove and burn affected leaves.
The leaves are liable to become covered, on the upper surface, with a sooty deposit, imperfect conditions of species of Capnodium. C. Persoonii has been recorded from Roses on the Continent; but probably the species varies. The Fungus grows chiefly in the secretions of the Aphides so common on Roses; the dark crust obstructs access of light and air to the leaves. The best remedy is to get rid of the Aphides, and to clean the leaves, and keep them clean by syringing or sponging.
INSECTS. In Kaltenbach's "Pflanzenfeinde," nearly 100 species of insects are recorded as more or less hurtful to Roses, i.e., by feeding upon them as larvae or as perfect insects; and to that number many more could now be added. Hence, only such as are markedly hurtful to these favourite flowers are selected for notice here.
The roots may, at times, be damaged by larvae of Cockchafers, and other subterranean foes; but these need not detain us. The larvae of Agrilus viridis feed below the bark on stems of Roses, usually close to the origin of a branch. The beetles are from 1/5in. to 2/7in. long, rather narrow, and brassy-green or blue; they are not uncommon in the South of England. The twigs and young leaves are much injured by Aphides or Green Flies, of which five species are recorded, with descriptions and coloured figures, in Buckton's "British Aphides," as feeding on Roses. Of these, Siphonophora Rosae, S. rosarum, and S. dirhoda, are often very plentiful on Sweet Briar and on the Cabbage Rose, and also attack the wild Dog Rose. Evergreen Roses seem less liable to be injured by them. The other kinds of Aphides are less evidently hurtful. All of them may be treated in the same way. The remedies recommended under Aphides will be found useful. It is desirable to keep the plants as free as possible from these insects, alike because of the sap they abstract, and because of their excretions covering the leaves and obstructing the functions of the latter, as well as affording a medium for the growth of dark-coloured Fungi, which still further interfere with the welfare of the plants. The larvae of a small Moth (Spilonota roborata), and those of a Sawfly (Paecilosoma candidatum), bore into the pith of Rose-branches from May to July, of course killing them, and causing the leaves on them to wither. The latter insect has been observed near Oxford by Prof. Westwood, but is, fortunately, rare. The infested branches should be cut off and destroyed while still tenanted by the larvae. The leaves of Rose-bushes are devoured by numerous insects, mostly Moths and Sawflies. Of the larger Moths, there may be named the Lackey Moth, the Gold-tail Moth and its allies (see Liparis), the Vapourer Moth (see Orgyia antiqua), the Bufftip Moth (Pygaera bucephala), the Winter Moth (Cheimatobia brumata), and the Barred Yellow Moth (Cidaria fulvata). Each of these, save the last, will be found described under the headings quoted. Cidaria fulvata is a Geometer, about 1in. in spread of wings, with a slender body. It is yellow, with a broad, brown, angled band crossing the front wings, and a pale, triangular spot at the tip, bordered below by a short, dark streak. The larvae of these moths should be shaken or picked off the bushes, collected, and destroyed. Those of the Winter Moth live between leaflets united by threads of silk. The females of this very destructive species are unable to fly, since their wings are too small to be of use. Hence, they can be prevented from reaching the buds to lay their eggs in them, if the stems and supports of the plants have a belt of any sticky substance (e.g., tar, alone or mixed with grease) smeared on them, and occasionally renewed between November and January, since it is at this season that the moths emerge from the pupae in the soil.
Among the smaller Moths, a good many species of Tortricina (which see) feed in leaves of Roses, either joining the leaflets by means of silk threads, or rolling them up in tubes, in which the larvae live. They may either become pupae in these shelters, or may lower themselves, when full-fed, to the soil, in which they become pupae. The larvae have the habit of lowering themselves by silk threads when the branches are jarred, and advantage may be taken of this habit by placing something below to catch them. Among the commoner and more harmful are Lozotaenia rosana, Pardia tripunctana, Croesia Bergmanniana, and Peronea variegana; but a good many others might be named which feed on Roses, as well as on other plants. The larvae of all have much the same habits, and it would occupy too much space to proceed here to distinguish them from one another. In the large group of moths known as Tineina (see Moths), there are a good many that live on Roses. Some of these live in the same manner as the Tortricina; but the larvae of others, belonging to the genera Nepticula, Tischeria, &c., mine between the surfaces of the leaflets, and disfigure them with pale, wavy lines or blotches. These mines do comparatively little injury to the plants. When desirable, the larvae may be killed in them by pressure between the finger and thumb, and the numbers may thus be kept down.