

So- 



used the blue stone solution on the vines bordering the highway in order to prevent 

 passers by from stealing the berries. They soon observed that the treated plants 

 were free from attack by the mildew while the others suffered severely. 



As the resting spores live over the winter in the fallen leaves, it is advisable, 

 when practicable, to burn all atTected parts, and not to leave dead leaves and 

 twigs lying on the ground. 



Forms of Economic Iiiiporta)icc. — Following is a list of the chief economic 

 species. 



The late Blight and Rot of Potato — Phytophthora infestans (Mont.)DeBary. 



The Downy Mildew of the Grape — Plasuiopara viticola (B. and C.) 

 Berl. & DeToni. 



The Downy Mildew of the Cucumber — Plasuiopara cnbensis (B. & C.) 

 Humphrey. 



The Onion Mildew — Pcroiwspora schlcidcniana. DeBary. 



The Downy Mildew of Clover and Alfalfa — Pcronospora trifolioni)ii. De 

 Bary. 



Mildew of Lima Beans — Plasuiopara phaseoli Thaxt. 



Lettuce Mildew — Brcmia lactucae Reg. 



THE DOWNY MILDEW OF CLOVER AND ALFALFA.— This disease 

 is worthy of special mention here, because, as far as I have been able to find out, 

 it has not before been reported as a disease likely to be troublesome in America. 

 In the summer of 19 12, however, it was the cause of considerable injury to the 

 first crop alfalfa on the Macdonald College Farm. 



Symptoms. — The lower leaves of the plants are attacked first and the fun- 

 gus seems to prefer the part nearest the stem, although it is usually spread over 

 the entire leaf. Affected 'leaves turn whitish or yellowish, curl up and fall off. 

 The lower surface of the leaf is grey owing to the presence of a downy covering 

 of conidiophores and conidia. 



Morphology. — This fungus possesses the characteristic mycelium of the 

 family. The summer spores are produced as described above. Resting spores 

 also are developed within the tissues of the leaves. When the leaves fall to the 

 ground the resting spores remain alive throughout the winter and infect the 

 plants' in the following spring. 



Effect on the Host. — The plants are not killed, but the crop suft'ers. directly 

 through loss of leaves, and indirectly through the impaired vigour of the plants 

 owing to the loss of the leaves. 



Control. — Spraying is impracticable in the field. If the crop is cut early, 

 before the leaves containing the winter resting spores fall to the ground, this 

 should prevent, or at least minimise, infection the following year. A systematic 

 rotation of crops will do much to prevent this as well as other injuries. Alfalfa 

 should not be sown on soil that is known to have been infected during the previous 

 year. 



THE LATE BLIGHT AND ROT OF POTATOES. 



This is the oldest, best known and most destructive disease of the potato. It 

 is troublesome throughout Europe, the North-East United States and the potato 

 growing districts of Canada. 



Symptoms. — The disease usually appears after blossoming. The symptoms 

 begin to show about five days after infection. Characteristic spots are developed 



