Gardening in Californi 



CHAPTER XIX. 



TREATMENT OF THE COMMON DISEASES OF, AND INSECTS 

 INJURIOUS TO PLANTS. 



DISEASES of plants are many and varied, some being 

 the result of attacks of injurious insects, while others 

 are caused by fungus growth which comes from 

 improper nutrition and poor circulation, or from very sud- 

 den atmospheric changes: for example, from warm, balmy 

 weather which encourages rapid growth, to cold, harsh winds 

 which seem to chill the whole plant while checking its 

 growth. The plant in these conditions suffers particularly 

 from the fact that, on account of the soil being warm, 

 the roots continue sending up supplies of sap of greater quantity 

 than the leaves and soft stems (being so chilled and semi-para- 

 lyzed by the cold air) are able to assimilate, and thus there is 

 caused a choking of the sap-vessels which greatly weakens the 

 plant, so that it gets into a condition susceptible to an attack by 

 any disease. Unless the weather moderates so that the plant can 

 again make vigorous growth and throw off the attack, it may 

 suffer severely and take weeks and, sometimes even months to 

 recover. 



The most common of the fungus diseases is undoubtedly the 

 Powdery Mildew, which attacks leaves, stems, flowers and fruits. 

 It appears like a thin white powder at first over the leaves, after- 

 wards spreading to the stems, stopping at once and entirely the 

 further growth of the part attacked. It is propagated by spores 

 which increase with amazing rapidity, often dwarfing and some- 

 times killing outright the whole plant. There are several kinds 

 of Mildew including the Rose Mildew, the Grape Vine Mildew, 



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