Nov. i6, 1914I Pecan Rosette 171 



and acid phosphate aggravate the disease, while nitrate of soda and 

 sulphate of potash seem to have a beneficial effect upon diseased plants. 

 The fertilizer tests with pecans point toward the conclusion that rosette 

 is also a nutrition trouble. 



PROBABI<E NATURE OF PECAN ROSETTE 



Rosette of pecans evidently belongs among the chlorotic diseases of 

 plants grouped by Sorauer ' into two main classes: (i) Noninheritable 

 and noninfectious diseases due mostly to improper nutritive supply or to 

 injurious physical conditions, and (2) inheritable and infectious diseases 

 due probably to enzymatic disturbances. From the results of the experi- 

 ments and observations outlined in this paper it seems legitimate to 

 conclude that pecan rosette should be placed in the first class of chlorotic 

 diseases — viz, those nontransmissible diseases caused by improper 

 nutritive supply or injurious physical conditions. 



From the definite sequence of a considerable number of symptoms in 

 pecan rosette it would seem more probable that the disease is directly 

 caused by one set of conditions which, however, may be indirectly 

 influenced by other conditions such as amount of rainfall, etc., rather 

 than that this same set of symptoms may in different localities be caused 

 by entirely different sets of conditions. Such a statement can not be 

 laid down as a demonstrated fact, but the general knowledge of both 

 plant and animal pathology renders it extremely probable. 



The spike disease of pineapple, to which reference has previously been 

 made, has been rather clearly demonstrated to be caused by improper 

 nutritive supply, and it seems rather probable that pecan rosette is of 

 a similar nature. From its wide distribution pecan rosette is clearly not 

 confined to any one general soil type, but it is entirely possible that in 

 those soils subject to the disease the proper balance between two or 

 more soil ingredients may not be maintained. For example, the effects 

 of a lack of proper balance between lime and magnesium are fairly well 

 known, and it is possible that some such condition as this may be responsi- 

 ble for rosette. Indeed, the results of our preliminary fertilizer experi- 

 ments point in this direction. The lime used was a high-grade stone 

 lime purchased in barrels, but its content of magnesium was not known. 

 The percentage of rosette was distinctly higher in the plots treated with 

 lime, but in the absence of an exact analysis of the lime used it can not 

 be determined from these tests whether the injury came from the Ume 

 alone or whether magnesium played a part in causing the disease. How- 

 ever, the chemical analysis of subsoil from the Davenport orchard, at 

 Belleview, Fla. (see p. 163), would seem to show that lime of itself is not 

 injurious. In this orchard the only type of subsoil entirely free from 

 pecan rosette gave by analysis 0.58 to 9.68 per cent of lime, 3.44 to 8.32 

 per cent of phosphorus, and 0.82 to 1.09 per cent of magnesium, all com- 



' Sorauer. Paul. Haudbuch der PflanzenkranUieiten. Aufl. j. Bd. i. p. 308. Berlin, [1906]. 



