98 DISEASES OF CROP-PLANTS 



distributed, and this in turn depends on the form of nozzle and 

 the amount of pressure apphed. 



Spraying machines range from power outfits with petrol 

 engines, through various forms of hand-operated tank or barrel 

 pumps, to knapsack types and hand-syringes. In the choice of 

 a type the nature of the ground to be worked over and the 

 spacing and height of the plants are first considerations. There 

 are few local crops to which power or traction sprayers can be 

 adapted. The most practical is usually some kind of wheeled 

 tank with a hand-pump attached, and, according to the power 

 of the pump, one or two 50-feet lengths of hose. Additional 

 wheeled tanks of convenient form may be used to keep the 

 sprayers supplied with fluid. 



Knapsack sprayers of the ordinary type require in the tropics 

 more than ordinary endurance on the part of the carrier to 

 maintain a satisfactory pressure. The compressed-air type, 

 consisting of tanks charged by a separate pump, is the best for 

 use in situations out of the reach of wheeled tanks, and may be 

 used by climbers for sprajdng coconut trees. The Abol type 

 of syringe is very useful for small spraying jobs in gardens. 



The mist-like discharge required for good spraying will not 

 carry far, consequently the nozzles have to be raised to nearly 

 the height of trees to be sprayed by means of bamboo rods, 

 which can be used up to about 10 feet in length. 



The aim in spraying should be thoroughly to cover the plant, 

 while keeping the drip from the leaves to a minimum. The 

 quality of the work can only be judged after the spray is dry, 

 and expertness is only to be acquired by practice. 



Spray injury. 



Damage to foliage from Bordeaux mixture is notoriously 

 erratic. It is agreed that the scorching effect which may develop 

 from properly prepared mixture depends a good deal on the 

 weather, being often increased by dull humid conditions. The 

 susceptibility is greater when the leaves are young and when 

 they are approaching senescence, and may be much increased 

 by insect injuries which in themselves are little noticeable. 

 Different varieties of the same plant species often show great 

 differences in susceptibility. There is little information on the 

 subject with regard to tropical plants and conditions. On 

 cotton the effect of too strong an application is the shedding of 

 the incipient flower budo 



Lime sulphur injury is less dependent on external conditions, 

 and may be met by reducing strength or in extreme cases by the 

 use of the self-boiled wash. 



Both copper and sulphur sprays often show a distinct tonic 

 effect on vegetation apart from their fungicidal action. 



Dusting. 



The application of fungicides in the form of dust has been 



