DISEASES AND PESTS OP PLANTS. 29 



LEAF-CURL (Exoascus deformans). 



This disease appears to be present wherever peaches are grown. The most 

 characteristic symptom is indicated in the name " leaf -curl." Attacked leaves shovf 

 an excessive growth in the soft tissues between the veins, causing a pocket-like 

 bulging towards the upper surface. If badly attacked the leaf also curls upon itself. 

 The affected areas have a bleached yellowish or a red colour instead of the normal 

 green, and finally become covered with a greyish bloom due to the formation of a 

 minute velvety layer of spore-sacs. In addition to the leaves, young shoots may be 

 attacked, being thicker and shorter than healthy ones. It was formerly supposed 

 that the fungus was carried over from season to season largely as perennial mycelium 

 in such shoots. We now know, however, that this method of over-wintering is only 

 responsible for a very small proportion of the spring infection. Infection takes 

 place almost, if not entirely, while the resting buds are unfolding in the spring. 

 Where an attack has been severe enough to cause extensive defoliation the new 

 leaves that are put out will remain quite healthy. The spores that cause infection 

 are apparently lodged on the bud-scales, and as soon as these are forced apart 

 sufficiently to allow of the spores being washed against the young leaves inside by 

 rain, infection may take place. Cold, wet weather at this time greatly increases 

 the chances of an epidemic, probably because it keeps the leaves from outgrowing 

 the susceptible stage as rapidly as would otherwise be the case. Accurate data on 

 the relative susceptibility of different varieties are difficult to procure, but it seems 

 to be generally agreed that the Elberta is the most susceptible. 



Control.- It has been found that one spraying with any good fungicide will 

 almost entirely control this disease. It is essential, however, that the spraying be 

 thorough, otherwise the spores protected under the edges or amongst the hairs of 

 the bud-scales will not be reached. It is also necessary that the application be made 

 at the right time. If the bud-scales have opened sufficiently to allow of spores being 

 washed by rain against the enclosed young leaves there is danger of infection taking 

 place. Once any green is showing it is too late to prevent some infection. So far 

 as the leaf-curl itself is concerned, good results are obtained if the spraying is con- 

 cluded a week or two before the buds swell. In most cases, however, the grower 

 has also to combat the peach-worm, and this makes it desirable to modify the spray- 

 ing so as to make it effective, if possible, for both purposes. Lime-sulphur, winter 

 strength, put on so that the application is completed at, or just before, the time the 

 buds begin to swell, will not only control the leaf-curl, but will destroy many of the 

 over-wintering larvae of the peach-worm. 



POWDERY MILDEW (&i>li<rr<itltcca ixtnnosa). 



This forms a white mouldy growth over the young twigs, leaves, and fruit. It 

 usually occurs as spots and patches, but may cover the entire surface. Leaves of 

 affected twigs are pale, narrow, and distorted, giving the twig a ragged appearance. 

 The disease was very serious in the Southern Okanagau last year, a large proportion 

 of the fruit being affected. Fruit with large mildew-spots on it is unsightly and 

 hence unsaleable, but a more serious consequence lies in the fact that rot organisms 

 enter very readily through the affected spots. Hence even slightly affected fruit 

 does not stand up well in transit and such fruit should not be shipped. 



Control. Owing to the sensitive nature of the foliage of the peach, the summer 

 sprays, such as lime-sulphur solution, used on other orchard trees cannot be employed. 

 Where thorough spraying for leaf-curl is carried out, however, mildew is often 

 lessened. Dusting the trees with flowers of sulphur when the dew is on, or after 

 rain, at intervals of ten to fourteen days will reduce it, or self-boiled lime-sulphur 

 may be used. It is claimed for Atomic Sulphur that it is very effective against this 

 disease; 4 to 5 Ib. to 40 gallons of water is the strength recommended, to be applied 

 soon after the petals fall, or, at any rate, as soon as the first indications of mildew 

 are observed. Whatever substance is used, special care should be taken to cover 

 the young fruit. 



