18 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
second or third year of phylloxeration. Such a vine as has been 
portrayed generally dies in the fifth or sixth year from the initial 
attack. 
As has been pointed out above, the decline of a vine is influenced 
by many conditions, and the hypothetical case given shows the mini- 
mum longevity of an established susceptible vine after phylloxeration. 
Under favorable conditions infested vines live much longer, and in 
extreme case? their length of life seem? hardly affected by the con- 
tinued presence of the insect on their roots, a slight decrease in the 
size of the crop being the only evidence of injury. 
HOW THE PRESENCE OF PHYLLOXERA IS INDICATED. 
The existence of the phylloxera in a vineyard is indicated by the 
well-known areas or " oil spots." so termed because oi their man- 
ner of spreading. A " spot " appears first in the form of one or 
two vines showing a slight shortening of the canes and a premature 
seasonal yellowing of the leaves, although the latter symptom may 
be caused by the red spider (Tetranyehus bimaeulatus Harvey), or 
by alkali in the soil. The year following this indication the vines 
originally infested exhibit a more noticeably stunted appearance. 
while other vines surrounding them show slight shortening of canes 
and premature discoloration of foliage. After this the " spot " in- 
creases in size, in course of time the vines in its center die. and 
finally the vineyard may become totally destroyed. The writers have 
never observed the " spots " to increase as rapidly in California as 
they are reported to have done in the vineyards of France after the 
time the insect first reached that country, when 2,500,000 acres were 
destroyed in 25 years, and vineyards frequently have been observed 
in California which had phylloxera " spots " of more than 20 years' 
standing to have vines still living. 
The " oil spot " generally is circular in shape, but sometimes it 
assumes other forms. At times it is oval or narrowly elongate, the 
latter form occurring on hillside vineyards through which water 
rills run in the spring. In such cases spread of the " spot " is often 
rapid in a downward direction, indicating that running water is 
an extra factor in the spread of infestation. The writers have 
demonstrated by experiment (see "Diffusion of phylloxera." p. 100) 
that the phylloxera? can be carried in water from one vine to another, 
and when the rains of March and April occur there are plenty of 
active phylloxera? on the roots. In other cases the spread of a " spot " 
follows the direction of the prevailing winds and it aj^pears that this 
spread is caused by wind agency in the transportation of wandering 
larva? in summer and autumn. In vineyards where vines are planted 
rectangularly (i. e.. S by 1:2 feet), instead of square, the infestation 
