CHAPTER IV 

 FUNGOID PESTS 



INTRODUCTION. In the treatment of fungoid pests it is essential to 

 know that parasitic fungi may be placed in two groups, each with a different 

 mode of development, and each necessitating a different method for their 

 prevention or cure. The first, or epiphytal group, includes those fungi which 

 establish themselves on the surface of leaves, stems, or other green parts of 

 living plants, their whole career being external and superficial. Many of these 

 can be held in check or destroyed by powdering or spraying. The Hop Mildew 

 and Rose Mildew are familiar examples of this class, the first being kept in 

 check by the application of sulphur, and the second by spraying with potassium 

 sulphide solution. In the early stages of attack the mildews present themselves 

 as patches of white mould consisting of a stratum of delicate interwoven threads, 

 forming a mycelium, from which arise fertile threads producing myriads of 

 spores to carry on the infection. Later in the season other spores are 

 formed which will rest during the winter, and germinate in the following 

 spring. 



The second group of parasites are endophytal, originating in the tissues 

 of the host-plants, and manifesting themselves externally only when the 

 damage is beyond control. In these cases all efforts must be directed towards 

 destroying the spores, and preventing the future infection of healthy plants. 

 The " rot moulds " belong to this group, and are among the most devastating 

 of fungoid pests. The mature mould, when it appears on the surface, pro- 

 duces a profusion of spores, or conidia. From these there issue minute 

 zoospores provided with delicate cilia enabling them to swim in any thin 

 film of moisture. If this be on a leaf, the zoospore may enter one of the 

 stomata, and give rise to a mycelium within the tissues. From this there 



issue fertile threads, reaching the surface through the stomata, to carry on 



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