102 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



American vines may probably be prevented by spraying the vines in 

 winter to kill the winter eggs ; but this treatment has no effect on the 

 root forms, which in California hibernate abundantly in the soil. 



All forms of the phylloxera are extremely minute, the root form 

 being about one twenty-fifth of an inch long when it reaches the adult 

 egg-laying stage, and little more than half this length when young and 

 active. It is just large enough to be seen by the unaided eye in a 

 good light when its presence is known, and, by the help of a glass 

 magnifying five diameters, its legs and antennae are plainly visible. 

 Its color is light greenish-yellow in summer, and somewhat darker in 

 winter; so that when numerous the attacked roots appear as though 

 dusted in spots with powdered mustard or cinnamon. The newly 

 hatched insect is fairly active, and at first moves about from place 

 to place on the roots, but finally, when it reaches the egg-laying stage, 

 inserts its sucking-tube into the root and remains fixed. 



Nature of Injury. The amount of nutriment taken from the vine 

 by such minute insects, even when present in the immense numbers in 

 which they sometimes occur, is not sufficient to account for the dis- 

 astrous effect upon* the plant. The death of the vine is due to the 

 decay which sets in wherever the phylloxera inserts its sucking-tube, 

 for a swelling is produced, composed of soft tissue, which soon decays. 

 When this swelling occurs at the end of a young rootlet, growth in 

 length is stopped ; when it occurs on larger roots, a kind of ' ' cancer ' ' 

 or decay spot is finally formed, which soon extends around the root, 

 and all below the point of attack dies t 



During the first year or two after a vine is attacked there is little 

 apparent damage. In fact, the effect of the phylloxera is equivalent 

 to root pruning, and in some cases results in an unusually large crop 

 of grapes. The year after this crop, however, the vine having endured 

 the double strain of heavy bearing and root injury, is unable to 

 recuperate, and generally dies. In rich moist soil the death of the 

 vine is not so sudden, and two or even more crops may mature after 

 symptoms of the disease are evident. 



Methods of Dispersal. The ways in which new vines and vineyards 

 become infested may be classed as natural and artificial. The natural 

 ways may be inferred from what has been said of the life history of 

 the insect. From a vine first attacked the root form spreads through 

 the soil to neighboring vines slowly, but continuously, thus forming 

 the so-called ' ' oil-spots. ' ' A typical oil-spot of several years ' standing 

 will show several dead vines in the center, then a ring of vines with 

 very short growth and no grapes, next another ring where the growth 

 is not of normal vigor, but where the crop may be equal to or larger 



