CHAPTER XX. 



By 



SPRAYING AND SPRAYING MACHINERY. 



G. Fox Wilson, Spraying Expert to the Royal Horticultural Society. 



Much debate has taken ph\ce during 

 recent j'ears concerning the advantages 

 of spraying. 



Criticisms have been advanced on many 

 sides, but too often they have been based 

 upon an imperfect understanding of the 

 aims and methods of efficient spraying. 



To say that spraying is an absolute ne- 

 cessity in many cases is perfectly correct; 

 for without this disagreeable, and often 

 costly work, one cannot get the full yield 

 of either fruit or flowers, while the outlay 

 it involves is generally more than recouped 

 by the increased value of the crops ob- 

 tained. 



Spraying is too often unsuccessful, and 

 a few of the reasons for ill-success will 

 help to make clear where so many go 

 wrong. 



1. Ignorance of Pest.— This causes loss of 

 time, labour and money. 



2. Wrong Part of Plant Sprayed. — A 

 knowledge of the disease and the part of 

 the plant especially to be i^rotected are 

 needed for successful spraying. 



3. Applying Spray at the Wrong Time.— 

 e.g., spraying with a caterpillar wash 

 where the damage is actually due to a 

 fungus attack, or applying a summer 

 wash when trees are dormant. 



4. Poor Pressure. — The liquid is made 

 to leave the machine with little force. 

 This means the i:)enetration and wetting 

 power are insufficient to do the work 

 needed. 



5. Nozzles. — Frequently the wrong kinds 

 are used, producing too fine or too 

 coarse a jet for the particular object 

 aimed at. 



These are probably the commonest mis- 

 takes in spraying. 



There is one great difference to be borne 

 in mind in attempting to deal with insect 

 2")ests as compared with fungi. 



Spraying against fungi is almost entirely 

 preventive. 



Spraying against insects is usually for 

 the purpose of staying an attack already 

 begun. 



If insects are not actually present, it is 

 usually waste of time, labour and money to 

 spray. 



If the invasion of a fungus is permitted, 

 it will be likely to establish itself so firmly 

 in so short a time that spraying will gener- 

 ally be too late to check its serious 

 advance. 



Knowledge is required by horticulturists 

 as to the habits of the pests that attack 

 plants. 



Without this knowledge one cannot suc- 

 cessfully combat them, e.g., insect pests 

 may be divided into two great classes : — 



1. Insects that take their food by biting 

 or chewing, and 



2. Insects that take their food by sucking 

 the plant juices. 



The former, the caterpillars, weevils, 

 chafers, &c., must be killed by poisoning 

 their food, that is, by stomach poisons ; 

 the latter, aphis, psylla, scale, red spider, 

 &c., must be killed by a contact wash, and it 

 is in the latter case that penetration and 

 wetting i^ower of the spray fluid are 

 specially needed, and these can only be 

 obtained by the use of considerable 

 pressure. 



Stomach poisons should be made to 

 remain on the leaves, when they are dry, 

 preferably on the under surface, which is 

 often hairy or woolly, and therefore holds 

 the poison better than the shiny upper sur- 

 face, and there it is less easily washed off 

 by rain. Contact poisons must be put on 

 so that every insect is hit, and therefore 

 the under surface of the leaves must be 

 sprayed, as that is usually where the 

 insects are. 



