W. F. Bewley 129 



from a series where the wilt was just commencing to a series in an ad- 

 vanced stage after 30 days' wilting. All the plants recovered in the 

 shaded house, but only a portion in that which was not shaded. The 

 plants which did not recover in the unshaded house, being the badly 

 wilted ones, were probably desiccated before they had a chance to recover. 

 These observations appear to justify the conclusion that temperature is 

 a most important factor in controlling the Verticillium Wilt Disease of 

 tomatoes, while shading is valuable because it assists the plant, probably 

 by reducing transpiration. The minimum, optimum and maximum 

 temperatures for growth in pure culture of the strains of Verticillium 

 albo-atrum utilised for the inoculations were 4-4° C, 23-3° C. and 30° C. 

 respectively, and it will be seen that the optimum temperature for 

 infection coincides approximately with the optimum temperature for 

 growth in pure culture. Verticilliufn wdlt is distinctly a disease of 

 moderately low temperatures and is therefore most severe in the spring 

 and autumn. 



Soil factors. 



Experiments carried out with different soils show that there is no 

 obligate relation between Verticillium wilt and any particular soil type. 

 Generally speaking, however, plants on soils which contain a large amount 

 of humus show more disease than those growing on soils of a poorer 

 nature. Clay soils, in virtue of their greater water-holding capacity, are 

 cooler than sandy soils, and plants grown upon them are more prone to 

 wilt than those grown on the latter. 



III. CONTROL. 

 Investigations to determine the chemical agents best suited to 

 eliminate the disease organisms from the soil and also to ascertain the 

 efiect of different manurial treatments upon the incidence of the disease 

 are in progress and will be reported upon later. 



1. Cultural methods. 



Cultural methods for controlling the wilt disease have been devised 

 and tested with promising results in the Lea Valley. In places where 

 the disease has been common in previous seasons it is advisable to grow 

 a highly resistant variety such as Manx Marvel or Bide's Recruit. Care 

 should be taken to protect the plants from any check in their develop- 

 ment and to encourage slightly soft rather than hard growth. When 

 Verticillium wilt appears, the temperature should be raised until the 

 average day and night temperature is above 25° C. This may be done 



