56 



SCIENTIFIC AGRICULTURE 



October 



of terminal leaflets. As the injury pro- 

 i^re.sses the yellow areas become brown, 

 curl up and dry out. Thus the leaflet fin- 

 ally possesses a dark-brown, dried, up roll- 

 ed margin with a band of green in the mid- 

 dle bordering the midrib (see plate). The 

 remaining leaflets gradually become af- 

 fected so that the whole leaf is involved 

 (plate). When the season is hot and dry 

 such leaves shrivel comi)letely, the petiole 

 gradually dries towards the stem and 

 hangs limp so that a touch will cause it to 

 drop. Whole fields may succumb to this 

 injury in a period of two dry, hot, Aveeks 

 so that a "burned over" appearance is 

 given to the crop. Usually, however, the 

 upper, young parts of the plants escape 

 burning for a time owing to the fact that 

 the adult females prefer young growing 

 tissues for oviposition. It is not until the 

 eggs hatch and the nymphs begin to feed 

 that injury is noticeable in these parts. 

 The nymphs, because they do not migrate 

 rapidly, are restricted in their feeding to 

 the area in which they were hatched, con- 

 secpiently causing severe injury in that 



area. Adults, on the other hand, fly at the 

 slightest disturbance and thus their effect 

 is more distributed. 



During ccol moist weather the burning 

 is checked and this also applies to plants 

 which have' been sprayed with Bordeaux. 



Effect on Plant. 



The eggs are laid on the midrib and pe- 

 tiole of the potato leaf and when hatched 

 the nymphs feed mostly by sucking juice 

 from the larger veins in the upper part of 

 each leaflet. This reduces the supply of 

 sap for the smaller veins at the margin and 

 tip of the leaflets and accounts for the fact 

 that broAvning, rolling and drying out oc- 

 cur at the tip and margin. There is thus 

 a direct loss of sap from the leaves fol- 

 lowed by the death of large areas of leaf 

 tissue. This occurs at the time when max- 

 imum growth rate of tubers should occur. 

 Consequently, the tubers suffer and the 

 greater the area of foliage affected the 

 more severe the effect on the tubers. In 

 cases where defoliation is complete, o»r 

 nearly so, the crop is a total loss. 



I'JLATE I. 

 A. — Normal potato leaf. 

 B. — Leaf affected with hopperhurn. 

 (After N. Y. (Geneva).) Technical Bulletin 



