CHAP. XI.] NIK CONTROL OF [NSEI I PESTS OF CROPS. ng 



care being taken to sec that mosquitos cannot breed in them. After 



use, the whole machine should always be thoroughly cleaned out 

 .Hid washed through with clean water; this is especially necessary 

 with regard to hose alter using kerosine washes, as kerosine attacks 

 rubber and will quickly rot the hoses if these are not washed clean. 

 When in use rubber hose should not be bent at a sharp angle nor 

 should it be left lying about in the sun when the machine is not 

 actually working. As noted above, all insecticides must be well 

 strained before thej are placed in the machine-, to avoid unnei 

 sary wear of valves and the clogging of nozzles. It is useless to 

 keep a spraying equipment if it is not in efficient order when 

 required for use. but by attention to the above points it should 

 be found ready whenever wanted at short notice. 



Special Methods. 



Under the heading of special methods may be included various 

 means for tin- control of crop-pests which are. as a rule, only appli- 

 cable by entomological experts or at least under their direct control 

 and which are therefore scarcely within the reach of the ordinary 

 cultivator because they require specjal knowledge or precautions 

 or apparatus. Of such methods reference is made here to the 

 fumigation of living plants, the control of termites and burrowing- 

 animals by poisonous gases pumped into their galleries by special 

 machines, and the control of insect-pests by fungal and bacterial 



ases and by means of parasites. Legislative measures may also 

 be included here. 



Fumigation of living plants and trees for the control of pests, 

 such as Stales, which are very resistent to insecticidal sprays, is 

 used extensively in other countries especially in the case of fruit- 

 trees and has been applied in India with successful results. The 

 only reason why this method has not been used more extensivelj 

 in India appears to lie in the fact that Scale-insects do compara- 

 tively little damage to fruit-trees in India. In some cases, however, 

 it is a useful method for the treatment of a small number of affected 

 plants or trees to prevent extension of attack. The fumigant 

 commonly used is Hydrocyanic Acid j;as. produced by the action 

 of Sulphuric Acid on Potassium Cyanide, and this is found very 

 Onable precautions are taken. Plants should 

 never be fumigated when the foliage is wet ; the best time to fumi- 

 gate is in the early evening, so that the gas may act whilst the 

 leaves are dry and during the night. In the case of small plants 

 they may be covered with anj gas-tight shade, such as a light 

 framework covered with paper tightly pasted over. For trees a tent 

 of some sort is generally used and, if the work is being done on 



