24 INSECTICIDES, FUNGICIDES, AND WEED KILLEKS. 



which must be abundant as the immersion exhausts the soil. Sub- 

 mersion was recommended for the first time in France in 186-4 for the 

 destruction of insects in meadows and fields. In 1870 the same treat- 

 ment was applied to vineyards attacked by the phylloxera, and lately 

 it has been used to render forests wholesome. 



Submersion of Fields and Meadows. — The inundation of 

 meadows and fic'lds destroys the larvue of Coleoptera (beetles, weevils, 

 etc.) and the grubs of the Lepidoptera, of which the following are the 

 most important : (1) Melolontha vulgaris (white worm), larvae of the 

 may-bug (cockchafer). — Artificial inundations have been in general use 

 in Hungary since 1888 to destroy this larva. The meadows are sub- 

 insrsed for eight days, and after that time all the white worms have 

 disappeared. De- la Blanchere has, however, seen water remain 

 more than a month on ground infested with white worms without 

 these being destroyed. That is explained by the fact that the larva 

 of the cockchafer, very sensitive to moisture, to avoid contact there- 

 with buries itself at such a depth as protects it from inundations. 

 But it is only in impermeable ground that the white worm has the 

 time to withdraw itself from the action of water. In such ground 

 recourse should not be made to artificial inundation but to carbon 

 disulphide. During the two years of its evolution, the white worm 

 descends into the soil in October, to a depth of about 2 feet, so 

 as to pass the winter, beyond the reach of cold, and it is only in 

 spring that it ascends to the level of the roots to gnaw at them. Ac- 

 cording to the habits of this insect it is, therefore, in spring and in 

 summer that the ground should be flooded. (2) Phytonomus jnmc- 

 tatus, Fb. — The larvae of this weevil are destroyed by flooding almost 

 at the very outset. In America the cotton plantations are flooded to 

 destroy the numeious parasites in the soil. (3) Agrotis segctVDi, 

 W.V. (grey worm grub of the dart moth). — Flooding to destroy 

 this insect ought always to take place in summer. In many cases 

 flooding of the fields by the excess of moisture exerts a vexing effect 

 on plants by retarding the ripening of the crops, or by developing 

 adventitious plants or parasitic fungi. It is not so, however, with 

 all crops, and it has been observed that submerged beets have more 

 vigour and resist the fungi which ravage them better during drought, 

 such as the Plioma tabifica, the disease of the petiole of the leaves, the 

 Pleospora jmtrefaciens or the heart rot, and the bacillus of the hacillary 

 gummosis of vine. These diseases being less intense after submersion 

 the method is advantageous. 



Submersion of Forests. — Anderlind has shown the great service 

 which the submersion of forests can render in the destruction of the 

 insect ravagers of w'oods, the larvae of which find a shelter under the 

 moss and humus surrounding the stocks. In the different countries 

 where submersion is in use the most dangerous insects only occasion 

 insignificant damage, it is therefore one of the most powerful preven- 

 tive measures against great invasions of cei'tain forest parasites. The 

 following insects are destroyed by submersion : Melolontha vulgaris, L. 

 (common cockchafer). Weevils injurious to conifers : Hylobius AbiAis, 

 L. (large spruce fir weevil). The Scolytides so injurious to deciduous 



