236 MAINE AGRICULTURAL EXPERIMENT STATION. I907. 



the stems and drying the terminal leaves. See Fig. 25. The 

 time of severest attack apparently varies somewhat, but the 

 infestation for the past 3 years in Maine has not been excessive 

 before early August and is entirely over with before the middle 

 of September. Under conditions favorable to Aphid growth, an 

 attack of less than 2 weeks' duration suffices to kill the potato 

 stalk for a distance from 4 to 6 inches from the tip, and the 

 growth of the tubers on plants thus weakened must necessarily 

 be affected. Aside from the direct weakening of the plant due 

 to the loss of sap and the withering of the tissue, the danger to 

 the health of a plant thus attacked by plant lice is considerable. 

 Although exceedingly minute, the beak of the plant louse makes 

 a wound which becomes in a short time surrounded by a dis- 

 colored area, readily detected by the unaided eye. As these 

 wounds extend for some little distance into the plant, a favor- 

 able location for the entrance of bacterial or fungus disease is 

 thus secured even where the infestation of plant lice is not 

 excessive enough to wither the tips of the stalk. Moreover 

 it is perfectly possible for insects to carry fungus spores from 

 diseased to healthy plants. Where the plant lice are abundant 

 the leaves are covered with honey dew which is soon attacked 

 by a dark fungus, and which together with the molted skins 

 adhering to the sticky substance, gives the leaves an unhealthy 

 appearance and must interfere with their natural function. 



The same species has at times been extremely abundant upon 

 the potato in Canada and the following quotation from Doctor 

 Fletcher's report for 1904 is of interest in this connection both 

 because of the seriousness of the infestation and the fact that 

 the time of appearance at Mahone Bay where the observations 

 were made was earlier than it has been in Maine. 



"Potato Aphis (Nectarophora solanifolii, Ashm.). — Potatoes are not 

 often troubled with plant lice in Canada ; but at long intervals outbreaks 

 have been observed on this crop, and such a one occurred last summer 

 at Mahone Bay, which was closely watched by Doctor Hamilton. 



'Mahone Bay, June 28. — I send you some aphides from potatoes which 

 are abundant enough to have appreciably blighted my potato plants.' 



'July 10. — The aphis on my potatoes has overrun the whole patch, with 

 the result that the potatoes have stopped growing and look very 

 unhealthy. The blossoms have withered up and fallen, the lower leaves 

 have turned yellow, and many others have turned black, just as if smitten 

 with the blight, and are falling. They occur in immense numbers. Their 



