570 INSECTS AFFECTING VEGETATION 



superabundance of moisture. Where leaf curl is due to pruning, 

 the pruning should be discontinued, or deep plowing, and plowing 

 rather close to the plant, followed. This plowing will in a measure 

 relievo the soil of the surface moisture, and at the same time do a 

 considerable amount of root pruning. In this way we cut off a 

 portion of the moisture that would otherwise be taken up from the 

 soil. (Fla. E. S. B. 91.) 



Mosaic Disease. The so-called mosaic disease, which is com- 

 mon to tomatoes, is characterized by a peculiar yellow spotting of 

 the upper surface of the leaves. These yellow spots, particularly 

 when exposed to bright sunlight, subsequently become purplish in 

 color, and the margins of the leaves curl up. We have observed 

 many crops badly affected with what is termed mosaic trouble, and 

 in all cases this is associated with too extensive pruning. The more 

 a tomato plant is pruned the more likely it is to be affected with the 

 mosaic disease, and topping or pruning of the leaders induces this 

 trouble more than other methodis of pruning. 



The mosaic disease is apparently a functional trouble, and little 

 is known about it. Similar troubles are associated with tobacco 

 (calico) and are believed to be infectious. The presence of this dis- 

 ease on tobacco is thought by some to be associated with certain 

 methods of transplanting. The disease on tomatoes does not destroy 

 the foliage of the plant, but the abnormal metabolic processes which 

 appear to be associated with this disease apparently affect the yield. 



Sleeping Disease or Wilt. The disease does not usually show 

 itself until the plants have attained full size and begun to bloom. 



Clinton characterizes the disease as follows: At first a lower 

 leaf or two will wilt, turn yellow and finally die. Gradually the dis- 

 ease works up, successive leaves drying up and dying on the vines. 

 Microscopical examination shows a discoloration of the vascular 

 bundles of the leaf petioles and stems, which are more or less filled 

 with the mycelium of the fungus. This causes a clogging of the ves- 

 sels and interferes with the transference of water, resulting in wilting. 

 The fungus infects the plant through the soil, and sterilization might 

 succeed in preventing infection. 



SWEET POTATO DISEASES. 



Sweet Potato Black Rot. The most conspicuous sign of the 

 disease, and the one w r hich distinguishes it from other diseases, oc- 

 curs upon the potatoes themselves. It consists in the presence of 

 dark, somewhat greenish spots, varying from a quarter of an inch 

 to 4 inches in diameter, sometimes covering the greater part of the 

 root and extending some distance into the tissue. These spots when 

 once seen can not be mistaken, as they are simply sunken areas with 

 distinct margins, like spots burned into the potato with a metal dye 

 which has left the skin uninjured. Should the slightest doubt as 

 to the identity of the disease remain after a superficial examination, 

 the removal of a small portion of the skin exposing the olive-green 

 tissue below would dispel it. Among the sprouts, or young plants 

 grown in hotbeds, the disease manifests itself in dark lines upon the 

 lower portion of the shoot and sometimes of the lower leaves, giving 



