BULLETIN 192. INSECTS INJURIOUS TO THE VINE. 103 



than that of the healthy vines. Such a spot enlarges its area year after 

 year at a gradually accelerating rate as the front of the invading army 

 becomes longer. The rate of advance will vary with the soil and climate, 

 but will probably never exceed forty or fifty feet annually. If this 

 were its only method of spreading, the insect could be controlled or even 

 exterminated with comparative ease. Unfortunately, it is able to 

 spread much more rapidly by means of the winged form; and the 

 rapidity of its extension over the south of France was due principally 

 to this agency. In California, though the winged form has been found, 

 it seems to be rare, especially in the central valleys, which probably 

 accounts for the comparative slowness with which new districts have 

 become infested. The artificial methods of dispersal here are probably 

 more effectual in spreading the insect than the natural. The insects 

 are taken from one part of the vineyard to another on pieces of the 

 roots of infested vines adhering to the plows or other implements used 

 in cultivation; while they are introduced into new localities on rooted 

 vines or cuttings brought from infested districts. 



METHODS OF COMBATING THE PHYLLOXERA. 



The methods to be used in resisting this foe of the vineyardist may 

 be divided into groups corresponding to different stages of infestation 

 and to varying local conditions. There are three cases to be distin- 

 guished, viz : 1. When the district is uninf ested ; 2. When a few small 

 infested spots are known in the district; 3. When the district is badly 

 infested; i. e., shows many and widely distributed infested spots, even 

 though none of the spots are large. 



1. In the first case, all efforts should be directed to keeping out the 

 pest, and the only effectual means is a rigidly enforced embargo on all 

 material capable of introducing it. Although the phylloxera, so far as 

 known, feeds on nothing but the vine, there is always danger of eggs 

 or insects being contained in the earth attached to any kind of root. 

 This measure, consistently carried out, has kept the province of Algiers 

 free from infestation, though the neighboring province of Constantine 

 has been a prey to the pest for many years. 



2. In the second case, where the insect has already obtained a foot- 

 hold, the first step to take is to determine as nearly as possible the 

 exact extent of the infested area. If it is found to be confined to a 

 small, isolated vineyard, an effort should be made to completely eradi- 

 cate the pest. This can be done only by destroying the vineyard, by 

 subjecting it to what is called the "death treatment." This is best 

 done (after grubbing up the vines and burning them on the ground) 

 by making an embankment around the whole vineyard and then 

 running water on to it until it is converted into a lake. The water 



