596 INSECTS AFFECTING VEGETATION 



to seventy bushels of air-slaked lime per acre would be a cheap and 

 effective means of securing the desired alkalinity. It would be pref- 

 erable to make this application in the autumn, or at least before the 

 ground is turned, so that the lime would be well distributed. (N. 

 Y. [Cornell] E. S. B. 163.) 



SUGAR CANE DISEASES. 



The Red Rot of Sugar Cane. This is a disease which is pretty 

 widely distributed in the tropical sugar countries at present, it being 

 known in Java, India, Hawaii, Madagascar, West Indies, and prob- 

 ably in other countries. In places, in certain years, it causes a very 

 large loss. At present also, the trouble seems to be quite widely dis- 

 tributed in the southern United States. I have found it in eight 

 parishes in Louisiana during the past year. Specimens from Cairo, 

 Georgia, where the trouble seems to be causing considerable damage 

 have been seen. It is also present and doing considerable damage in 

 at least two counties of northern Florida. The specimens which were 

 received from southern Louisiana during the past spring have shown 

 the disease to be quite severe in places and to be responsible for part 

 of the poor stands during the season. 



The disease is caused by one of the small imperfect fungi, known 

 to botanists as Colletotrichum falcatum. The fungus does not usu- 

 ally fruit profusely in nature, though occasionally the fruiting pus- 

 tules may be found on dead parts of the plant or in lesions on the 

 main stem. The fruit pustules appear to the naked eye as very small 

 black specks. 



The red rot disease is not easily recognized in a field of growing 

 cane for the reason that the disease is almost entirely on the inside 

 of the stalk. The exterior of the cane may look perfectly normal, 

 while the interior may be badly diseased. Where the disease is very 

 severe, the leaves may turn yellow and wilt ; but it is hardly probable 

 that we will find this condition at present in Louisiana. However, 

 in cane that has been planted or windrowed, the disease may develop 

 so well that it will show on the outside of the cane. Many of the 

 eyes will be dead, and there will be black dead areas extending out 

 from the nodes. There may also be somewhat sunken dead lesions 

 on the stalks, especially on the upper joints. 



However, the disease is 'best told by splitting the stalk and ex- 

 amining for the characteristic red color of the tissue. The whole in- 

 side of the stalk will not be red, but the color will be more or less 

 irregulanly distributed, the red being usually in streaks or bands ex- 

 tending out from the nodal region. There are also frequently white 

 spots surrounded by the red tissue. These white spots are local cen- 

 ters of growth of the fungus. A microscopical examination of these 

 spots will show the cells of the host plant to be crowded full of the 

 mycelium of the fungus. In badly diseased stalks, there are strips 

 also of brown tissue, generally just beneath the rind. Often also the 

 pith of the cane will split, leaving a cavity which becomes filled with 

 the mycelium of the fungus. 



The presence of red rot in cane that has first been attacked by 

 borers cannot be so readily told. Borer attack alone will cause a red- 



