DISEASES AND PESTS OF PLANTS. 41 



cases the fruit may wither up before the cane as a whole dies. Fruit-spurs and 

 leaves are commonly sent in for examination by those ignorant of the nature of the 

 disease, in the belief that the cause of the trouble will be found there. This is not 

 the case, however, the drying-up of the berries, leaves, and other portions of the cane 

 at one point being due to the failure of the sap-supply, which in turn is due to the 

 destruction of the sap-conducting tissues at some point lower down the stem. Such 

 canes, if examined carefully below the wilted portion, will show the presence of dead 

 brittle areas, lighter in colour than the healthy parts, and which may extend all 

 around the cane. Fruiting-bodies are formed in the outer layers of the bark of the 

 aftectt-d areas and are visible as minute dark-brown or black points. The surface of 

 the cane in their vicinity is often covered with a smoky-brown powder of escaped 

 spores. The fungus probably gains entrance in most cases through wounds. It is 

 probable also that it can exist for an indefinite time on fragments of dead canes in 

 or on the ground. 



Control. This is a difficult disease to control. In starting a plantation every 

 care should be taken to secure healthy stock. Affected canes should be removed as 

 completely and as soon as possible and burned. Refuse, such as broken canes, etc., 

 should be collected and burned. Raspberries should not be planted again for a 

 considerable time on land that has borne a badly diseased plantation. Spraying has 

 so far proved of doubtful value. 



CROWN-GALL. 



Raspberries often suffer severely from this. Such plants can be detected by the 

 yellow, unhealthy foliage and stunted appearance of the plant. They should be dug 

 out carefully and burned and only some non-susceptible variety of plant put in their 

 place. Any plant found infected when the plantation is being set out should not be 

 planted, but destroyed. 



ROSE. 



POWDERY MILDEW ( Spit wroth eca pannosa). 



This is well known to rose-growers, being the commonest fungus enemy of the 

 rose. There is a great difference between different varieties in regard to suscepti- 

 bility, the Crimson Rambler being. one of the worst. The fungus, like other powdery 

 mildews, forms a white or grey mouldy growth over the leaves, young shoots, and 

 flower-buds. On this mycelium numerous spores are produced through the season, 

 and by means of these the fungus is enabled to spread rapidly. Affected leaves 

 wrinkle and curl up and the young shoots are distorted. Later in the season little 

 black fruiting-bodies may be formed in the mycelium, but commonly these are not 

 noticeable. Sudden changes of temperature render the plants more liable to severe 

 attacks of the disease. 



Control. In mild cases dusting with flowers of sulphur when the dew is on or 

 after rain is of benefit. Spraying with potassium sulphide (liver of sulphur), */& oz. 

 to a gallon of water, is more effective, but the sulphur in this form acts upon the lead 

 in white-lead paint to produce a black-lead sulphide. Hence, if used to spray rose- 

 bushes against a verandah or other structure painted white, the results may be very 

 disconcerting. In such cases the flowers of sulphur should be tried. The potassium 

 sulphide solution must be made up afresh each time, as it decomposes on standing. 

 When lime-sulphur is on hand it may be used instead at a dilution of about 1 to 30. 

 It may be necessary to discard the most susceptible varieties. 



RUST (Phragmidium subcorticium ) . 



This is a very common disease. In the early part of the season it appears as 

 orange-red pustules on the stems, leaf-stalks, leaf-veins, and calyx. The orange-red 

 colour is due to the formation at these points of enormous numbers of summer spores. 

 Later in the season these are replaced by black masses of resting spores. No satis- 

 factory control measures are known, one difficulty being the abundance of the disease 

 on wild roses. However, although disfiguring, it rarely causes serious injury. 



