TOMATO DISEASES 143 



denly and dry up. The disease progresses more rapidly 

 in plants that have made a succulent, luxurious growth, 

 while those with hard, woody stems resist it somewhat. 



The disease is due to the invasion of bacteria, which 

 enter the leaves through the aid of leaf-eating insects, 

 or through the roots. They plug the water-carrying 

 vessels of the stem, shutting off the water and food 

 supply of the plant. If the stem of a plant freshly 

 wilted from this disease be severed, the bacteria will 

 ooze out in dirty white drops on the cut surface. 



Remedial measures entirely satisfactory for the 

 control of bacterial wilt have not yet been worked out. 

 The best methods to adopt at present are the following : 



(1) Rotation of crops. The field evidence is that 

 this disease is in many cases localized in old gardens 

 or in definite spots in the field. It appears also that 

 the infection left by a diseased crop can remain in the 

 soil for some time. It is therefore advised that tomato 

 growers should always practice a rotation of crops, 

 whether any disease has appeared or not, and that in 

 case bacterial wilt develops they should not plant that 

 land in tomatoes, potatoes, or eggplants for three or 

 four years. The length of rotation necessary to free 

 the soil is not known, but will have to be worked out 

 by the individual grower. 



(2) Destruction of diseased plants. The bacteria 

 causing wilt not only spread through the soil but are 

 carried by insects from freshly wilted to healthy plants. 

 Diseased plants thus become dangerous sources of in- 

 fection, and it is evident that all such should be pulled 

 out and burned. This is particularly important at the 



