GARDEN PESTS IN NEW ZEALAND 



CHAPTER X. 



Principles of Pest Control. 



IN" dealing with the control of plant pests, the objective is to prevent 

 attacks, or, when the attacks have established, to check them as 

 much as possible. In the latter case the term "exterminate" is in too 

 f reqnent use ; it is not usually practicable to exterminate a pest, and the 

 best that can be done is to check or control it. 



In the control of animal pests, it should be borne in mind that the 

 pests are usually associated with other factors inimical to plant life, 

 such as unthrifty plants, due to injury or malnutrition, and fungous 

 and bacterial diseases, any one of which might be either the primary or 

 secondary cause of plant injury. 



Though at times one method may serve as a means of control, 

 generally it is a combination of methods that gives the most satisfactory 

 results, rendering the conditions favourable for the plant and unfavour- 

 able for the pests and diseases. The principles underlying control are : 



(a) Garden management. 



(b) Use of chemicals. 



(c) Influence of natural enemies. 



(a) Garden Management. 



All parts of plants, both above and below ground, are subject to 

 infestation by pests and diseases. Under garden conditions, cultivation 

 is intensive, and plants are grown year after year on the same ground 

 in surroundings much more sheltered and crowded than in the open 

 field. Sound garden management is therefore an important control 

 factor, and the following features are fundamental: 



CONDITION OF SOIL. The vigour of plants is dependent on the soil, 

 which therefore must be kept in the right state; it must be well tilled, 

 and must contain the requisite nourishment and moisture available for 

 plant use, and as far as possible be free of an abnormal population of 

 root feeding pests, such as eelworms and the larvae of many insects. 

 Proper cultivation is therefore the important factor in bringing the soil 

 into .the state most favourable to plant life, as all inimical factors, 

 including pests, are reduced. Wherever practicable, as in glass-houses, 

 soil-inhabiting pests and diseases can be completely controlled by steam 

 sterilisation. 



IMPORTATION OF PESTS. One of the readiest methods of infesting 

 a garden is the importation of pests on plants, and every care should be 

 taken to secure only pest-free stock. In this respect, also, must be 

 mentioned the use of stable and barnyard manure, in which pests such 

 as insect larva?, woodlice and eelworms are introduced; artificial ferti- 

 lisers are therefore safer. 



