1920.] 



Insect and Fungus Pests. 



375 



INSECT AND FUNGUS PESTS IN 



JULY AND AUGUST. 



It is proposed to include periodically in this Journal 

 notes on insect and fungus pests which are likely to be 

 troublesome in tlie month following publication. In most 

 cases the damage done by the pests which are obvious on the 

 various plants at this time of the year cannot be checked, 

 but it is hoped that the notes will help growers and others 

 to recognise the pests attacking their crops so that they 

 may take steps in following years to prevent a similar 

 attack. If growers are uncertain as to the nature of any 

 particular pest or disease, a specimen, carefully packed in a 

 tin box, should be sent to the Ministry, 72, Victoria Street, 

 London, S.W. i, for identification and advice. 



Vegetables. — In most parts of the country Potato Blight 

 may be expected to appear about the middle of July ; 

 it had already, b^^ the middle of June, appeared in the south- 

 west. Its general appearance is now fairly well known, but for 

 the benefit of those who have not seen its early stages it may be 

 stated that the disease usually appears first in the shape of 

 one or more blackish spots or blotches on the leaflets. On 

 looking at the under surface a similar spot will be found, but 

 this is surrounded b}^ a white or greyish ring of mould. This 

 mould is composed of the fine filaments or threads of the 

 fungus, which have come to the surface of the leaf to produce 

 the spores or " seeds " of the disease, which the wind spreads 

 broadcast. As the disease is internal, little or nothing can 

 be done to check its course in the plant, but its spread to 

 healthy plants should be prevented by spiaying with Bordeaux 

 or Burgundy mixture. Copper salts, the poisonous constituent 

 of these mixtures, are very deadly to germinating spores, and, 

 if sprayed on the plant in a neutral (non-acid) form, so that a 

 thin film remains on the leaves, the plant is protected from an 

 external attack. Germinating spores coming into contact 

 with the copper salt are killed and, therefore, unable to enter 

 the leaf. 



The question as to whether Potato Disease will become 

 epidemic rests very largely with the climatic conditions. In 

 the south-west and in Ireland, where summer conditions 

 are usually warm and damp, spraying of potatoes is absolutely 

 essential if a healthy crop is to be obtained, but in England 



