. Canadian journal of agricultural science. Agricultural Institute of Canada; Agriculture. 56 SCIENTIFIC AGRICULTURE October of terminal leaflets. As the injury pro- i^ 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 th
. Canadian journal of agricultural science. Agricultural Institute of Canada; Agriculture. 56 SCIENTIFIC AGRICULTURE October of terminal leaflets. As the injury pro- i^ 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
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