PECAN ROSETTE. 15 



muriate of potash, in the other with nitrate of soda. The two limed 

 plats free from rosette received in addition cottonseed meal and 

 Thomas phosphate, respectively. In the five plats without lime no 

 rosette at all developed with the exception of doubtful signs in two 

 trees immediately contiguous to a limed plat. The four lime-free 

 plats showing no traces of rosette were the control, untreated, and 

 three plats treated respectively with muriate of potash and acid 

 phosphate, stable manure alone, and stable manure with ground 

 iDone. During this period no other cases of rosette developed in the 

 vicinity of the experimental block, though cases appeared in other 

 parts of this orchard of 700 acres. In two other fertilizer tests where 

 the disease was already present at the start, it increased somewhat 

 in severity of attack or in the number of new cases in the plats 

 receiving lime. 



Analyses of the subsoil around normal pecan trees in parts of an 

 •orchard free from rosette gave 0.5 to 9.5 per cent of calcium. It 

 appears then that the disease is not caused by the presence of lime 

 alone, since more lime occurred here than in parts of the orchard 

 -where rosette was present. Ash analj^ses of normal and diseased 

 leaves and twigs showed only slight or highly variable differences. 

 Apparently, however, the percentage of potassium is greater in the 

 diseased leaves and twigs. 



In one spray test with Bordeaux mixture on rosetted trees nega- 

 tive results were obtained. 



It is evident from numerous orchard records covering periods of 

 2 to 12 years that pecan rosette fluctuates from year to year without 

 any variation in fertilization or cultural methods. The diseased 

 trees may apparently make a complete recovery and remain normal 

 for an indefinite period, or after one or more years may again con- 

 tract the disease. However, in the majority of cases of recovery 

 observed, the trees had not reached the stage where the branches 

 were dying back. It seemed thus (56, p. 165, 169) highly probable 

 that seasonal climatic changes, such as variations in precipitation or 

 moisture content of the soil, might have at least an indirect relation 

 to the prevalence of rosette. In large orchards the more or less 

 simultaneous appearance of rosette in patches, and its usual limita- 

 tion to these areas, suggested some connection with soil phenomena. 



From the apparent nontransmissibility through the seed, negative 

 results in attempts at isolation of organisms, the apparently nega- 

 tive results of budding and grafting between normal and diseased 

 trees, and the results of transplanting tests it was concluded that 

 the disease was probably nonparasitic. 



From pruning and " dehorning " tests, transplanting and fertilizer 

 experiments, dynamiting of soil around rosetted trees, and from 

 orchard records of disease fluctuation it was at that time considered 



