172 Journal of Agricultural Research (voi.iii.no. 3 



puted as oxids. Lime was present as both carbonate and phosphate. 

 It will be noted that the magnesium content was low. Considerable clay 

 was present in all these cases and frequently with a considerable admix- 

 ture of creolin. 



The possibility of some relation to soil organisms is not entirely pre- 

 cluded, but it is thought that the direct cause will ultimately be found 

 in some lack of balance in the nutritive supply, or possibly in some 

 toxic organic substance or substances in the soil. The large group of 

 physiological diseases to which pecan rosette seems to belong consti- 

 tutes one of the most bafHing series of problems now before the path- 

 ologist; and although a large number of workers have been investi- 

 gating these diseases, none of them has as yet been fully worked out, 

 either as to cause or control. 



CONTROL 



No great or constant difference in varietal resistance has been observed 

 among the common orchard varieties. In one orchard a certain variety 

 may have a much higher percentage of rosette than some other variety, 

 but in another place the relative amount on the same two varieties is 

 just as likely to be reversed. This has been shown clearly by orchard 

 records in widely separated localities. Evidently the difference in 

 apparent resistance in such cases is due either to a differenc in soil con- 

 ditions in the two parts of the orchard or to a difference in the resist- 

 ance of the stocks to the inciting cause. That there is sometimes a 

 difference in the true resistance of the stocks seems evident from the 

 fact that of two trees of the same variety growing side by side (i foot 

 to several rods apart) one may have rosette and the other appear per- 

 fectly normal. If the cause of the disease lies in the soil, as appears 

 to be the case, such an influence of the stock would naturally be expected. 

 There appears to be little doubt then as to the existence of a difference 

 in the resisting power toward rosette, but orchard records and observa- 

 tions tend to show that this difference is usually manifested through 

 the stock rather than through the variety worked upon it. 



It should be added that until more is definitely known as to the direct 

 cause of pecan rosette little can be said of its control by use of resistant 

 stocks or by other methods. Good care and fertilization are to be 

 recommended, but until more is known of the lime-magnesium balance 

 in relation to rosette, orchardists should test the effects of lime upon 

 a few trees before using it on a commercial scale. The use of copper 

 sulphate upon the soil, though favored by many growers, can hardly 

 be recommended as a remedy for rosette without more conclusive data 

 as to its efificacy than have yet been forthcoming (see p. 162). The results 

 of our experiments have shown that pruning as a remedial measure is 

 of no avail. Since there is no e\'idence that pecan rosette is trans- 

 missible from tree to tree, the cutting out of orchard trees showing 

 only traces of the disease is hardly to be recommended, because they 



