KEENEL-SPOT OF THE PECAK" AND ITS CAUSE. 11 



ANALYSIS OF RESULTS. 



Of the 313 nuts confined with bugs in the field and IT in the 

 laboratory (a total of 330), 323 had typical kernel-spot and most 

 of these, especially the Curtis, were very severely spotted. Of the 

 91 checks in the field and 15 in the laboratory, totaling 106 nuts, 

 all were entirely free from any evidence of kernel-spot. The results 

 reported seem to leave little doubt as to the association of pecan 

 kernel-spot with sucking insects, therefore confirming the investiga- 

 tions of Turner (6). 



It has been suggested that the insects involved may possibly trans- 

 mit with their piercing mouth parts some microorganisms to the 

 pecan kernels which cause the characteristic spotting effect. With 

 this supposition in view, the cultural work in the laboratory was 

 carried out. Of portions of over 400 separate spots that were 

 planted on beef and corn-meal agar, more than half proved to be 

 sterile. Rand's Coniothj^rium was not observed in any of these 

 cultures. If either a fungus or a bacterium was responsible for the 

 spotting, it is logical to assume that a large percentage of cultured 

 kernel spots would in suitable media develop the causal organism. 



Cultures from affected kernels have shown that most of the spots 

 are sterile, while among those developing fungus or bacterial growth 

 no single type of organism has been found constantly associated with 

 the diseased condition. Furthermore, typical kernel spot's can be 

 produced readily by confining stinkbugs with immature pecans. It 

 is, therefore, also logical to conclude that pecan kernel-spot can be 

 d'rectly attributed to injuries inflicted b}- sucking insects, in this case 

 to the southern stinkbug {Xesara viridula). The pathological result 

 m.ay be caused by the mechanical rupturing of the host cells, by the 

 sucking up of plant juices, by injection of toxic substances into 

 the tissues, or by the combined result of all three types of injur;y. 

 No study was made to determine the pathological effect of the punc- 

 tures, but Figure 5 would lead one to suspect that the injury is due 

 to the extraction of juices from the tissues affected and to the me- 

 chanical injury of the cells. 



CONTROL MEASURES. 



The writer has done no work in view of demonstrating the practi- 

 cability of controlling pecan kernel-spot. Dr. C. A. Van Duzee, an 

 extensive pecan grower of Cairo, Ga., has been practicing clean culti- 

 vation in his orchard for several years. He reports that since this 

 practice was adopted his nuts have been free from kernel-spot. 



It is the writer's opinion that clean cultivation can not be recom- 

 mended unless stable manure can be supplied to the orchard soil 



