DISEASES AND PESTS OF PLANTS. 



means that the protective structures and living matter are reduced to a minimum, 

 while the cells are charged with sugars, acids, and other substances which stimulate 

 the growth of parasitic fungi. Every effort should be made by the grower to secure 

 varieties which are not only commercially desirable, but which have been shown by 

 experience to be resistant under local conditions to the diseases of the locality. In 

 the case of short-lived plants, it is often possible for a grower, by the use of a little 

 care in the selection of seeds or tubers from resistant plants, to develop a strain 

 greatly improved in resistance under the grower's own conditions. 



GENERAL METHODS OF PREVENTION. 



(1.) Endeavour by proper cultivation, pruning, fertilization,, etc., to keep the 

 plant in a thrifty, vigorous condition. This does not mean forcing. The production 

 of an excessive sappy growth is one of the most important conditions predisposing 

 to disease, and one which the cultivator in irrigated districts is especially tempted 

 to bring about. 



(2.) Collect and burn diseased parts of plants, crop refuse, primings, etc. Many 

 parasitic or partially parasitic fungi can exist for an indefinite time as saprophytes 

 on such material, only waiting the opportunity to once more attack living plants. 

 Such refuse also harbours all manner of insect pests. 



(3.) Try to avoid the first introduction of disease into your land or orchard. Go 

 to sonic pains to get your stock from a nursery or other source free from disease, 

 lleject any plants that are diseased at the time of setting out. Many diseases are 

 carried in or on seeds and may be widely spread in this way. In some cases it may 

 be advisable to disinfect the seed by soaking it for fifteen minutes in a 1 to 1,000 

 solution of corrosive sublimate. This will do much to prevent the introduction into 

 this Province of such diseases ,-is club-root or tinger-and-toe of cruciferous plants. 



(4.) Practise rotation wherever possible. Where a crop has been attacked by 

 some disease, follow it, if possible, for two or three years by crops immune to that 

 disease. In this way many parasites may be starved out. Even where this is not 

 possible owing to the omnivorous character of the parasite, much good may yet be 

 done, since a fungus capable of attacking different crops often becomes increasingly 

 virulent towards one particular crop if allowed to grow and reproduce for generation 

 after generation on that crop. 



(.".) Xitnn/hi!/. This is dealt with more fully in another part of the bulletin. 

 Sprays applied to woody deciduous plants during the dormant season are generally 

 made strong enough to kill all spores with which they come in contact. Such sprays, 

 however, are usually so strongly caustic or poisonous that they work serious injury 

 to the soft green parts of plants. Hence sprays adapted for use during the growing 

 season have to be made much weaker. The spray material in this latter case forms 

 a continuous thin layer over the surface of the plant through which the fungus-hypha 

 from a- germinating spore must make its way. and in attempting to do so is killed. 

 Sj traying of this kind is entirely protective, and must obviously be repeated often 

 enough to keep the film of spray material there and to protect the new growth. It 

 must also be even enough to avoid the occurrence of unprotected spots large enough 

 for a fungus-spore to fall and germinate without coming in contact with the spray 

 film. When the minute size of fungus-spores is considered, it will be realized that 

 this means very thorough spraying. Once a parasite has obtained entrance to a plant 

 spraying can do little or nothing. It is now amongst the cells of the host-plant, and 

 anything which would reach and kill it there would also kill the plant-tissue, so that 

 in a very real sense the cure would be worse than the disease. Superficial parasites 

 like powdery mildews may, however, in some cases be killed by spraying even after 

 they have got a foothold. 



(6.) Promptly report and send in for identification any disease with which you 

 are unfamiliar. By doing so you may be rendering the Province a service in report- 

 ing the first appearance of a disease which may still be prevented from establishing 



