February, '21] fenton: potato tipburn 79 



3. The older the nymphs the greater the amount of injury done, 

 n\-mphs in the first and second instars being incapable of producing 

 any effect on the leaf unless in numbers. 



4. The greater the number of nymphs on a leaf the sooner the injury 

 develops and the more rapidly the leaf or plant is killed. 



5. The adult hopper is not nearly so effective as any of the nymphal 

 stages but will produce the disease when concentrated in large numbers 

 on a given plant. 



6. The disease is produced to the same extent and just as soon under 

 such diverse environmental conditions as type of soil, amount of mois- 

 ture in the soil, presence or absence of sunlight, or reduced leaf transpira- 

 tion. 



7. Tipburn as a disease is localized, being confined to that part of 

 the plant exposed to the attack of the leafhoppers, whether this be a 

 leaflet or entire branch. 



8. Other insects known to feed on potato such as Buffalo treehopper 

 mTnphs, tarnished plant bugs, potato aphis, and flea beetles, produce a 

 type of injury characteristic of the individual species concerned but in 

 no way resembling tipburn. 



9. Bordeaux mixture prevents tipburn by repelling the ovipositing 

 female leafhoppers. 



President Wilmon Newell: This subject is now open for discus- 

 sion. 



Mr. R. L. Webster: I would like to ask if any allowance was made 

 for unavailable soil moisture; that is, sand as compared with loam? 



Mr. F. a. Fenton: We kept certain potted plants in a pan of water 

 all the time, and we also kept them where the sand or loam was dry. 

 There is a difference in the plant growth but not in percentage of tip- 

 bum. 



Mr. R. L. Webster: There would be considerable difference in 

 loam. 



Mp. F. a. Fenton: We found that we got tipburn just as quickly 

 on plants in good rich soil as in sand. I noticed in traveling about 

 the state that the type of soil seemed to make little difference. For 

 instance, one field had but one spot that was badly tipbumed and that 

 was in a low part where there had been much water. Tipburn is always 

 correlated with the number of leafhoppers. We found out, too, that the 

 disease, you might call it such, is not systemic, that is, it does not travel 

 from one part of the plant to another without the agency of the leaf- 

 hopper. 



