CHAPTER I. 



COLD WATER— SUBMERSION— SPRAYING HOT WATEE^ 

 IMMERSION— SPRAYING— HYDROGEN PEROXIDE. 



I. Water, H.^0. — Water is necessary to the plant (1) as food, (2) as 

 solvent of nutritive matters. To a certain extent crops increase in 

 proportion to the water used in the cultivation. Want of water 

 injures the plant, causes deformities, anomalies, and troubles of which 

 the chief are : pilosis, excess of hair on the stem and leaves, formation 

 of tart substances (piquants), stony pears, lignification of the roots ; 

 nanisme, potatoes with filiform rhizomes, fall of flower-buds, pre- 

 mature drying of the leaves, honey -dew, barren flowers in the case of 

 cereals. But on the other hand, if water is useful and even necessary 

 to the plant, in excess, however, it is injurious thereto. In the latter 

 case it is the cause of the following diseases : frisolee of the potato, 

 rhytidome of the potato, germination of the same plant before potato 

 lifting, hollow fruits, stems and roots, premature formation of seeds, 

 dropsy, gourmands, hypertrophy of the roots, cellular rottenness, 

 frondescence, phyllodia or chloranthia, asphyxia of the seeds and 

 roots, putridity of the seedlings. 



Use. — Water serves as a solvent or vehicle for most of the agents 

 used to combat plant diseases ; but it can by itself alone serve as an 

 insecticide in many cases, and as it is cheap it is profitable to use it. 

 Cold or hot water is used as follows, according to circumstances : 

 Cold water : Submersion ; spraying. Hot water : Immersion ; spraying. 



(a) Cold Water, Submersion. — Submersion or artificial inunda- 

 tion asphyxiates the insects living or refuging in the soil. It consists in 

 placing the area of the ground to be treated under water for a period 

 of from two to sixty days, according to the nature of the soil and the 

 kind of parasites to be destroyed. The soil must only be slightly per- 

 meable, the ground must not be on a slope, and it must be near a source 

 of water capable of furnishing 6000-30,000 cubic metres per hectare (2| 

 acres), and to maintain it at that for a certain time. Submersion is not 

 efficient unless it be complete, so that it may soak deeply into the 

 inundated ground and be executed under certain conditions. The 

 submersion of fields and vineyards is in use in different countries of 

 the globe, and everywhere gives encouraging results. The costs of 

 submersion are not great when near a river from which the water can 

 be led ; the expense in that case only amounts to 41 francs per hectare, 

 say 13s. per acre. But when the water has to be brought by elevating 

 machines then it may amount to 200 francs (£8) per hectare, say -63 4s. 

 per acre. To this amount must be added the co=t of manuring. 



