THE CARE OF ROSES

Press, Volume CV, Issue 30958, 14 January 1966, Page 6

THE CARE OF ROSES

Roses are extremely popular and can be found in most gardens —together with attendant pests and diseases which seem forever to be prevalent and plaguing wherever they are grown.

The prevalency of some, such as black spot or mildew, can have a considerable debilitating effect on the plant, even to the extent of limiting the numbers of the following year’s blooms. Other aliens likely to upset satisfactory growth and flowering include rust, aphids, mites and scales. By means of a regular spray programme it is possible to provide continuous immunity to their incursions.

Black spot is an extremely common fungus disease to which no rose variety, as far as I know, is immune, although certain varieties seem to be more susceptible than others. Its presence is made evident by black or purplish spots noticable on either side of the leaves and occasionally on the stems. It becomes more evident at this time of the year and can cause premature leaf fall on. some roses. Warm, moist conditions favour germination of spores which can over winter on fallen leaves or may be carried over from season to season on diseased stems.

As it can be extremely difficult to eradicate once it has gained control of a leaf, by reason of the fact that it lodges under the outer waxy covering or cuticle of the leaf protection must be given from the onset of the new growth. Continuous applications of such materials as colloidal sulphur in cool weather, copper oxychloride when hot, or captan, ferbam, or thiram at any time will provide a suitable safeguard. Burning of fallen leaves and prunnings is also worth while. Susceptibility

AU parts of the rose bush above ground level are susceptible to powdery mildew fungus disease and in particular young leaves. Infection of the latter may cause them to curl, become more purplish, redden, yellow and finally fall. Young canes may be infected for some length from the tips and may die in cases of severe attacks. Badly infected flower buds may not open as sepals and petals become welded together. Although a damp atmosphere is conducive to infection, germination of disease spores is greatly inhibited by moisture on the leaves and overwintering on the plant in colder regions such as Canterbury is also greatly reduced.

Excessive nitrogen feeding should be avoided as this reduces the hardening of plant foliage, thereby making it more prone to attack by powdery mildew. The use of the specific material for combating this disease, karathane, can be recommended while sulphur as a dust or spray has proved most satisfactory in the past and can still be used.

Not all species are susceptible to attack by rust, a disease which becomes most conspicuous from now on. It is a disease which is not as widespread as the previously mentioned two, but, as it can produce fresh spores every 10 to 14 days under suitable conditions on leaves which have been moist for at least four hours, its damaging effect is often far greater. Red pustules are noticeable on the underside of infected leaves during the summer and these turn black with the changing season. Premature leaf fall can occur and existence can continue in young green wood. Early dusting or spraying is advisable where outbreaks are regular. Materials already recommended other than karathane can be used, although sulphur is best after rain. Other Menaces Silver leaf, virus and grey mould may also be problematic at times and, although cutting back and pruning of infected areas is the only cure for silver leaf, the fungicides already mentioned are effective against the others.

Aphids, or “the blight,” are an ever-present menace to the well-being of roses and their sap-sucking activities cannot only transmit virus

from a diseased to a healthy plant but can also cause severe weakening of the subject. Where inspection and protection are not regularly maintained the first sign of trouble usually noted is a severe puckering of the leaves. Malathion, lindane, and parathion are some suitable remedies to apply.

Discolouration of leaves from a healthy green to various hues of brown betray the presence of infestation by red mite. These can be observed either feeding by sucking or running about on the underside of the leaf. Prevalency is increased under dry conditions; control by using such materials as the specific miticide, kelthane. Various scale insects, which are also found on other plants, may attach themselves

to the stems of roses. Again sucking is the mode of injury and winter, or red oil, applied during the late winter —or white oil at any time during the present and following month —will get rid of it. It is a pest likely to be found more usually on neglected subjects. A number of caterpillars are predacious on roses and, with the exception of leaf roller caterpillar, cabryl or D.D.T. will prove effective against them: D.D.T. is preferable where leaf roller is evident.

During hot, windy weather scorching can occur while wilting and growth retardation are likely under such continuous conditions when beds have become too dry and mulching has not been carried out.