SUBMERSION OF VINEYARDS. 207 



4TH. PERIODICITY OF SUBMERSION. 

 Submersion should be repeated every year. Although this 

 treatment may be considered as the most perfect insecticide, 

 if well applied under proper conditions, and although it is 

 often impossible to detect a single insect on the roots of 

 treated vines in spring, they are always attacked afresh every 

 summer, as proved by Faucon, by the aptrous form travelling 

 over the soil, .and by the winged forms carried by the winds 

 from neighbouring vineyards. It becomes necessary, there- 

 fore, to destroy every winter the insects which arrived during 

 the summer, to prevent their multiplication, which might 

 cause great damage. 



