78 PROTECTION OF PLANTS, 1917-18 



Groundsel {Senecio vulgaris L.) Several sprayings with 20% iron sulphate 

 will prevent seed-development. 



Bachelor's Button or Bluebottle (Centaurca cyanus L.)- This weed can be 

 checked by spraying with a 10% solution of sulphuric acid applied at the rate of 

 89 to 134 gallons per acre. 



Canada Thistle {Cirsium arvense Scop.). This plant when growing in grain 

 crops may be prevented from seeding by spraying with sodium arsenite (2 pounds 

 in 52 gallons of water) or common salt (150 pounds in 52 gallons of water) or iron 

 sulphate (130 pounds in 52 gallons of water). 



If sodium arsenite is used it should be applied when the grain is quite young 

 so that the poisonous compound may be all washed off the straw by rain before 

 harvest time. 



Summary. 



1. As in other parts of the country, weeds are a serious problem in the Prov- 

 ince of Quebec. 



2. Chemical methods are specially applicable in grain crops and on stony 

 or waste ground that cannot be cultivated. 



3. Most useful chemicals for the purpose, strength used, and amount per 

 acre. 



4. Results of some experiments at Ottawa. 



5. Destroying weeds by heat. 



6. List of Quebec weeds that can be checked by this method , 29 species in all. 



