KEENEL-SPOT OF THE PECAN" AND ITS CAUSE. 



13 



It is logical to conclude that greater vigilance in protecting the 

 pecan crop from kernel-spot will have to be observed during seasons 

 following winters with no extremely low temperatures, as there will, 

 no doubt, be a lower mortality of hibernating bugs. 



While the information leading to an explanation of the irregular 

 appearance of kernel-spot is meager, it is significant to record that 

 two very severe occurrences of the trouble have followed winter? 

 with no extremely low temperatures. 



There was a greater occurrence of kernel-spot during the seasons 

 of 1916 and 1921 than during any other years on record for southern 

 Georgia, while in this same region there was very little kernel- 

 spot during the seasons of 1917, 1918, and 1919. 



Table 4 shows the absolute minimum temperatures recorded by the 

 United States Weather Bureau at Thomasville, Ga., covering the 

 period from 1914 to 1921, inclusive, together with the prevalence of 

 kernel-spot. 



Table 4.- 



-Minimiim temperatures and kernel-spot prevalence at Thomasville, 

 Ga., 19H to 1921, inclusive. 



Years. 



Mini- 

 mum 

 tem- 

 pera- 

 ture 

 (°F.). 



Prevalence of kernel-spot. 



Years. 



Mini- 

 mum 

 tem- 

 pera- 

 ture 

 CF.). 



Prevalence of kernel-spot. 



1914-15 

 1915-16. 

 1916-17. 

 1917-18. 



23 

 25 

 13 

 15 



Abundant. 



Do. 

 Small amount. 



Do. 



191S-19. 

 1919-20. 

 1920-21. 



18 

 23 

 29 



Small amount. 

 Abundant. 

 Do. 



The correlation of kernel-spot with temperatures may be only a 

 coincidence. However, it is the writer's opinion that future obser- 

 vation will establish a record showing relationship of occurrence of 

 kernel-spot with winters of no extreme low temperature. 



While this investigation seems to clearly demonstrate that the 

 inciting cause of pecan kernel-spot is due to insects, the pathological 

 and physiological changes involved are apparently influenced by the 

 condition of the nuts at the time the punctures are made. Bugs, 

 confined in cages with mature pecan kernels that had been removed 

 from the shells, were observed for several clays by the writer. The 

 bugs feci upon the kernels constantly, but produced no evident in- 

 juries or spots resembling kernel-spot. This suggested that spots 

 can be produced by the bugs only when the tissues of the kernels are 

 soft and the cell walls can easily be ruptured by the sucking effect 

 of the insects involved. 



The history of the investigation of pecan kernel-spot and its path- 

 ological effect upon the host plant is parallel in ways to the disease 

 of carnation leaves -that Woods {8) designated as stigmonose and 

 proved by him to be caused by punctures of aphids, thrips, and red 

 spiders. This carnation trouble had previously been studied by 



