286 



Potato Spraying Trials. 



[JUNE, 



Blight was present on all the plots before the second spraying, 

 and was much more prevalent on this variety than on the 

 Evergoods. It spread very slowly until the second week in 

 September. Just after the middle of September the unsprayed 

 plots were killed off by blight, whereas the sprayed plots did 

 not die off for some time. On September iSth the percentage 

 of green in the tops was roughly as follows : — 



Per cent. Per cent. 



Plot I 2 Plot 5 . . . . 20 



,, 2 . . . . . . 20 ,,6 • . . . ID 



"3 50 7 •• •• 50 



,.4 2 8 .. ..2 



Up to that date Plot 5 looked the worst, owing to scorching. 

 Taking the season throughout, Plot 7 looked the best plot. 



The above table shows that there was a big variation in the 

 yields of the unsprayed plots. At the time of spraying it was 

 noticeable that the end of the field where the plots started was 

 not so good as where they ended, and as a consequence three 

 control plots were left. 



Spraying early with Bordeaux mixture made little difference 

 to the yield as compared with the nearest unsprayed plot. 

 Plot 7 was estimated before weighing to be the highest yielding 

 plot, as there was practically no scorching, and the tops lived 

 longer than Plot 8, which actually gave a higher yield. 



It is not possible, however, to account for the low yield of the 

 plot twice sprayed with Bordeaux, as there was little scorching 

 on this plot, and it was expected that its yield would be only 

 slightty lower than that of Plot 4. Plot 5 was expected to give 

 the lowest yield, as the scorching reduced the leaf area. 



Conclusion. — The above figures suggest that it is unsafe to 

 spray potatoes in the Fens in a season like 191 9. Many growers 

 throughout the Fens scorched the tops by spraying. 



After a period of hot, dry weather the leaves of potatoes are 

 hable to attacks of green fly (aphis), and under the same con- 

 ditions are liable to scorch when sprayed. It has been suggested 

 that the scorching is due to the entrance of the spray into the 

 punctures ■ caused by these insects. Until this question is 

 settled by experiments, growers are warned that by spraying 

 in hot, dry weather, when the foliage is attacked by green fly, 

 they risk a loss of crop through scorching. 



