14 BULLETII^^ 1102, U. S. DEPARTMENT OF AGRICULTURE. 



Arthur and BoUey {1) who concluded that the disease was caused 

 by a bacterium. In the case of pecan kernel-spot, Eand first con- 

 cluded that the trouble was caused by a fungus, and it is now proved 

 by the writer to be caused by insect punctures. 



Since the initial cause of pecan kernel-spot is entomological and 

 the result pathological, control measures can possibly best be worked 

 out by considering both factors. 



SUMMARY. 



Pecan kernel-spot has been reported from North Carolina, South 

 Carolina, Georgia, Florida, Alabama, Mississippi, Lfouisiana, and 

 Texas. 



Owing to the fact that the spots can not be seen until the shells of 

 the nuts are removed, and also because pecans from planted orchards 

 are usually widely distributed in small quantities to consumers, the 

 extent of the loss caused by kernel-spot is difficult to estimate. While 

 the nuts in some orchards will be entirely free from this disease, in 

 other orchards such a large percenfage of the nuts will be spotted 

 that the crop will be unmarketable. 



Kand conducted a laboratory investigation of kernel-spot in 1912- 

 13 and concluded that it was caused by C oniothyrium caryogenum. 



The result of the work of Turner in 1917 indicated that the spots 

 were caused by punctures of insects. 



In the present investigation, 250 clusters of Schley and Curtis 

 pecans were incased with wire cages. From five to seven specimens 

 of southern stinkbugs {Nezara mridula L.) were confined in 200 

 cages during a period of approximately five weeks for the Schley 

 nuts and two months for the Curtis. Fifty clusters were caged as the 

 others, but no bugs were placed in them. These served as checks. At 

 the end of the experiment none of the checks showed any signs of 

 kernel-spot. Of those nuts caged with bugs, 97.6 were spotted with 

 typical kernel spots. 



Nuts with which bugs were confined in a laboratory developed 

 typical kernel spots within 65 hours. No microorganism developed 

 from these spots in Petri dish cultures. 



Of 416 cultures made of kernel spots, 80 developed colonies of 

 bacteria, 71 grew fungi, and 265 remained sterile. 



No one organism was found constant in pecan kernels affected with 

 kernel-spot. Eight species of fungi and three of bacteria were iso- 

 lated in this experiment and considered to be saprophytic. 



All 11 forms isolated from affected kernels were inoculated into 

 healthy pecans. None produced spots resembling typical kernel-spot. 



The cause of pecan kernel-spot is attributed entirely to the me- 

 chanical rupturing of the host cells, to the sucking of the plant juices, 

 to the injection of toxic substances into the tissues, or to all three 

 types of injury. 



Possible control measures are suggested. 



