LEAF AND SEEDLING DISEASES 



181 



germinate directly by means of germ-tubes which infect 

 healthy seedlings. 



An excess of moisture is conducive to both these diseases. 

 Consequently good drainage is the most important inhibit- 

 ing factor. When seed-beds are attacked it is advisable to 

 allow the free play of air currents over the beds and to 

 remove any obstructing objects. Spaulding (1908) has 

 carried out trials with various powders and sprays. The 

 most satisfactory powder was either (a) a finely powdered 

 sulphur (that known as ' washed sulphur ' is apparently the 

 best), or (6) a mixture of powdered sulphate of copper 

 (one part) and slowly slaked, very finely powdered lime (ten 

 parts), the two being very thoroughly mixed together. The 

 powders should be applied three or four days after the 

 seedlings have come up, and from then onwards, after each 

 shower, for about two weeks. A weak solution of sulphuric 

 acid (1 oz. to 1 gallon of water) was found to be the most 

 efficient spray. This solution may be applied with an 

 ordinary sprinkling-can before the seeds are sown. 



