68 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



EECENT DEVELOPMENTS IN THE TREATMENT OF DISEASES 

 AND INSECTS INJURIOUS TO ORCHARD CROPS. 



By Professor S. A. Beach, New York State Experiment Station, 



Geneva, U.S.A. 



The last quarter- century has witnessed remarkable changes in the means 

 and methods used for combating injurious insects and plant diseases. 

 Greater achievements appear to have been made in this direction than 

 along any other line of general horticultural practice. During this period 

 investigators have continually been adding to our knowledge of the habits 

 and life histories of insects and parasitic fungi which are of economic 

 interest to the horticulturist. Many new fungicides and insecticides have 

 been tested. The best of these have been adopted by progressive 

 gardeners and fruit-growers in various parts of the world. Their practical 

 value is now generally acknowledged, even by those who do not avail 

 themselves of their benefits. 



These achievements have stimulated the progress of certain horticul- 

 tural industries, because they have established them upon a more secure 

 foundation by making it possible to protect plants and plant products 

 from the ravages of certain destructive enemies hitherto practically beyond 

 control. 



The introduction of Arsenical Insecticides. — Is it not strange that 

 former generations bequeathed to us so little knowledge of the use of 

 poisons for killing leaf- eating insects ? The introduction of Paris Green 

 for this purpose marked a new era in the use of insecticides and in the 

 development of spraying machinery. It is but little more than thirty 

 years ago that Paris Green was first used for poisoning insects. The 

 people of the northern portion of the United States of America, east of 

 the Mississippi River, were then regarding with grave anxiety the resistless 

 progress of the Colorado Potato Beetle, Doryjjhora decemlineata, from its 

 original home in the Rocky Mountains across a stretch of 1,800 miles of 

 territory to the Atlantic Ocean, threatening destruction to one of the most 

 important of the food plants of this region, the Potato, Solanum tubero- 

 sum. The discovery that a paint pigment known as Paris Green could be 

 relied upon to poison this insect without injuring the Potato plant was 

 naturally hailed with delight. It was finally demonstrated that this 

 remedy could be applied without poisoning the portion of the plant 

 which is used for human food and without sterilising the soil. So once 

 again an evident calamity proved to be a blessing in disguise. The much- 

 dreaded Potato Beetle drove men to the discovery of means of fighting 

 successfully not only this but many other injurious insects. Arsenical 

 compounds in one form or another are to-day largely depended on in 

 fighting leaf-eating insects as a class. 



Fungicides. 



The introduction of Bordeaux Mixture. — It is but little more than 

 fifteeh years ago that the discovery was made near Bordeaux, France, 



