418 



SCIENTIFIC AGRICULTURE 



August, 1922 



defined we have the "blotch" type and this is 

 often found in the cortical tissues. 



Frost injury before or during harvest may 

 give rise to any of these types or modifica- 

 tions of them biit as a rule the ring type pre- 

 dominates if exposure is short since vascular 

 tissues are more sensitive than parenchy- 

 matous, while the blotch type is common 

 with long exposures to chilling temperatures. 



(e) Net Necrosis or Vascular Discol- 

 oration 



In discussing Leafroll, Fusariose, and 

 Frost necrosis it was pointed out that the 

 term "net-necrosis" is applicable to any of 

 these tuber troubles if the delicate vascular 

 network is discolored. In discussing vascu- 

 lar discoloration Edson in 1920 says, "A 

 popular impression has prevailed that any 

 except the most superficial stem-end discolor- 

 ation might be taken as a trustworthy indi- 

 cation of the presence of Fusarium, or, at 

 least, that the stock was grown on vines af- 

 fected with Fusarium or Verticillium. Some- 

 what extensive preliminary observations and 

 cultural studies, made by the writer both at 

 the time of harvest and during or at the close 

 of the rest period, on stock grown in sec- 

 tions where Fusarium blight and wilt do not 

 occur, as well as in sections where they are 

 known to be general, show that, while Fusar- 

 ium and Verticillium undoubtedly do cause 

 vascular discoloration of potato tubers, dis- 

 coloration can not be accepted as proof of the 

 presence of Fusarium or, indeed, of any other 

 organism, nor can the absence of discoloration 

 be confidently accepted as proof of the ster- 

 ility of the vessels near the stolon attachment. 

 There seems to be reason to think that vas- 

 cular necrosis may often arise from purely 

 physiological causes and that it need not 

 necessarily be seriously abnormal, though 

 frequently it is." 



This author found that out of 3,042 plant- 

 ings from discolored tissues 1,352 gave no 

 growth. 



(d) Internal Brown Spot 



In this disease brown spots are scattered 

 through the flesh of the tuber and are not 

 confined to the vascular ring. The spots 

 consist of dead brown cells surrounded in 

 many cases by cork cells. It is possibly 

 something like stii)i)en in apples and is as- 

 sociated with unfavourable soil moisture con- 

 ditions at a critical jjcriod in the growth of 

 the tuber. 



(e) Spindling Sprout 



Weak spindling sprouts are likely to de- 

 velop frc m tubers affected by mosaic, leaf- 

 roll, fusarium necrosis, etc. and in all in- 

 stances such weaklings are best eliminated 

 from the crop. It is also found that potatoes 

 grown under unfavourable soil or climatic 

 conditions tend to give rise to spindling 

 sprouts when used for seed. Similarly the 

 same strains grown year after year will gra- 

 dually lose vigour and "run out" resulting in 

 weak progeny. It is advisable to sprout 

 potatoes before planting and to discard those 

 with thin, straffgling. spindling sprouts. 



(f) Hollow Heart 



This condition occurs as a result of the 

 too rapid growth of the tubers. Some va- 

 rieties, such as the Rural New Yorker, when 

 grown in rich soil frequently develop hollow 

 heart. The tissues surrounding the irregular 

 space in the heart of the tuber are brown 

 and lined with a corky laj'er. The trouble is 

 not serious from a pathological point of view. 



(g) Arsenical Injury 



This is not serious <when ordinary pre- 

 cautions are observed. Arsenic oxide is the 

 base of any arsenical spray used in control- 

 ling chewing insects and its use alone would 

 cause severe burning to the foliage. It is 

 therefore necessary to use it in a combined 

 form such as Paris green, lead arsenate, cal- 

 cium arsenate, etc. The arsenate is better 

 used in combination with Bordeaux so that 

 sufficient lime is present to prevent burning 

 of the foliage. Burning occurs where in- 

 sects have made injuries and in the axils and 

 margins of leaves where the insecticide is 

 likely to be held in quantity. The use of a 

 finer spray from high pressure nozzles will 

 usually prevent such accumulations of mater- 

 ial on the plant. 



GENERAL CONSIDERATIONS 

 IN CONTROL. 



1. Control of potato diseases by the grow- 

 er involves as a first essential that the grower 

 know the diseases which have to be control- 

 led. Every grower of potatoes on a large 

 scale ought to familiarize himself with sym- 

 toms and with the major points in the life 

 history of the causal organism if such ex-~ 

 ists. To do the right thing at the correct 

 time necessitates accurate knowledge. Infor- 

 mation can always be obtained from Mac- 

 donald College in Quebec, from the Ontario 

 Agricultural College in Ontario, from other 

 agricultural colleges throughout the Dominion 



