314 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



increasing rapidity of transport nowadays is leading to the importa- 

 tion of plants from abroad in ever-increasing amount, with the result 

 that fungoid pests are introduced with them. These may, or may 

 not, obtain a hold in this country, but when they succeed in establishing 

 themselves, as the potato disease and American gooseberry mildew 

 have, the consequences are often particularly serious. Unfortunately 

 these unwitting importations of disease are often made by persons 

 with little or no knowledge of the harm that may result, and the disease 

 is established ineradicably before it is recognized and means taken to 

 stamp it out. Such a state of affairs can only be dealt with by legis- 

 lation and a thorough control of such importations by the State, 

 though even under such conditions it is very problematical whether 

 diseases we do not at present possess can be kept out indefinitely. 



I propose then to deal briefly with the methods which are being 

 tried, for the most part experimentally, for the control of plant diseases, 

 limiting the subject to diseases caused by the attacks of parasitic 

 fungi. 



The most popular method unquestionably is to coat the plants 

 on which disease has either appeared or is expected to appear with 

 a dust-like film of some fungicide, appMng it in the form of a fine 

 spray or as a powder, preferably the former. Many fungicides are now 

 in use, some suitable for one disease, some for another. No universal 

 specific has yet been found, in spite of endless investigations during 

 the last decade or so. 



Of all the fungicides now in use, Bordeaux mixture is unquestion- 

 ably the most important. It can be relied upon to keep more than 

 one of the worst of the fungoid diseases in check, yet even in the case 

 of the potato disease (Phytofihthora infestans) large growers are occa- 

 sionally met with who consider that the drawbacks to its use are 

 greater than the undoubted benefits it confers. They argue that in 

 wet seasons, when the disease is most prevalent, spraying can only 

 be carried out with difficulty ; that the repeated sprayings frequently 

 necessary are costly ; that the preparation of the mixture requires more 

 skill than their employees possess ; and finally that spraying so delays 

 the maturation of the crop that it cannot be lifted until some three 

 weeks later than an unsprayed crop. The cumulative effect of these 

 drawbacks is that many prefer to risk the partial destruction of their 

 crops season by season. Yet this particular disease is perhaps more 

 readily kept within limits than any other serious one attacking our 

 crops, and moreover the mere coating of the plants with the fungicide 

 undoubtedly, apart from all questions of preventing losses, increases 

 the crop considerably. 



In such circumstances it is hardly to be wondered at that there 

 is a tendency nowadays to look for other methods of controlling the 

 outbreaks of disease caused by parasitic fungi. 



Where crops are grown under glass, and consequently such condi- 

 tions as temperature, water-content of the atmosphere, and again of 

 the soil are largely capable of control, a certain amount can be done 



