PLANT HYGIENE. 



73 



PLANT HYGIENE. 

 By F. J. Baker, A.E.C.S., F.E.H.S. 



[Read March 8, 1910.] 



The dread of plant diseases and pests is ever with us. If at the 

 moment free from actual attack, the warnings of investigators and the 

 advertisements of insecticides, &c., remind us of the existence of 

 innumerable minute foes that are stated to be ready to destroy our 

 treasures. The Conference on Spraying, held in October 1908, gave 

 an indication of what diversity of opinion there is concerning plant 

 diseases and the utility of the common methods of deahng with them. 

 We are continually being asked what should be done for this or that 

 trouble; and although quite easy to specify what is, for the time being, 

 considered the orthodox remedy, one has the feehng that more real 

 service could be given if it were possible to investigate the predis- 

 posing causes. If the exciting cause were removed, the effect would 

 tend to disappear. Generally, though not always, a specific fungus or 

 insect pest is present, but a thorough search will often reveal a general 

 unthriftiness, mistaken probably, in many instances, by the untrained 

 obsei-ver for unusually vigorous growth. Something may be learned 

 by going into glasshouse, garden, plantation, and field and searching for 

 plants apparently less thrifty than the majority, and comparing as 

 minutely as possible their surroundings with those of the more healthy- 

 looking. 



The important question to my mind is : What are the predisposing 

 causes of disease? Why is this plant the first or most badly attacked, or 

 w^hy is the disease more virulent in it? Very frequently, if seen soon 

 enough, there is no specific pest present, although usually an attack is 

 not long delayed. The endeavour to destroy pests by spraying often 

 results in ill-effects upon the plant, and not infrequently some other 

 trouble ensues. 



The chief causes of unthriftiness in plants are : Heredity, or in- 

 herited weakness ; structural imperfections ; adverse physical conditions 

 of climate, temperature, water, and soil; and last, but not least, mal- 

 nutrition. A plant of weak hereditary constitution may, under the 

 most favourable conditions of food, soil, and climate, develop into a 

 mature and useful plant. On the other hand, a plant of strong consti- 

 tution may be rendered useless by adverse conditions. It is very bad 

 policy for a cultivator not to take care to secure stock of the most 

 vigorous constitution, but it is worse to ruin that stock by improper 

 management. 



There appears to be very little doubt that in the near future scientific 

 research will do much towards breeding plants of strong constitution 



