11 Feb., 1918.] Disease!^ of Fruit Treei^. 101 



DISEASES OF FRUIT TREES AND THEIR TREATMENT. 



Bn H. [!'. Davty, F.E.S., Orchard Supervision Branch. 



The number of pests that attack cultivated plants is legion, many of 

 which are now cosmopolitan, and this to such a degree that their country 

 of origin is not alwayr; known for a certainty. It is well known that 

 many plants and animals thrive better in a new country, than in the 

 one to which they are indigenous. Some of the reasons for this is the 

 absence of natural controls such as climate or the absence of parasites, 

 either insects or fungi. An abundant food supply always favours^ this 

 increase, and it is easily seen that where such crops as fruit trees are 

 grown year after year thif/ ensures an unbroken food supply to the 

 pests attacking them, whereas the same pests attacking plants under 

 purely natural conditions would have to travel greater distances to find 

 suitable host plants:. 



In dealing with insect j^ests it should be borne in mind that the 

 mission of many insects is to assist nature in removing trees that are 

 low in vitality, so as to make room for healthy ones. This can easily 

 be proved by ringbarking a perfectly healthy tree, and noticing how 

 readily it is attacked by insects that previously left it alone. From 

 this we learn the necessity of keeping trees and plants in as thrifty a 

 condition as possible. In the economy of nature, many insects are 

 useful in lessening the seed production of some plants, and thus aid in 

 preventing their undue increase, but unfortunately they show no dis- 

 crimination when plants of a kindred nature are being grown for profit. 

 In combating injurious insects bv means of spraying, it is of the 

 greatest importance that this should be done thoroughly, and care 

 taken that no part of the sprayed plant is missed by the material, other- 

 wise such insects as aphides are in a very brief time able to again infest 

 the tree from a few surviving individuals. 



With insects that secrete waxy filaments such as Woolly aphis, the 

 nozzle of the spray pump should be held close up to the parts to be 

 sprayed, so that sufficient force may be applied to wash away the floc- 

 culent protective covering beneath which the insect shelters. 



The time of application, together with thoroughness, if combined 

 with some knowledge of the pest to be fought, is the essential for 

 success. Clean cultivation is also important, as, apart from its physical 

 effect on the soil, it also destroys cover for pests of various sorts. The 

 head-lands should be cultivated, for if allowed to support a riot of 

 weeds, these are a prolific source of invasion of enemies to the fruit- 

 grower. 



The chief insects which the horticulturist has to combat may be 

 grouped as follows: — 



1. Chewing insects that feed on exposed leaf surfaces. 



Examples. — Pear and Cherry Slug, Pumpkin Beetle and most 



caterpillars. 

 Treatment. — Spray with arsenate of lead. 



2. Chewing insects that are exposed for only a short time. 



Examples. — Codlin Moth, Light Brown Apple Moth. 

 Treatment . — Arsenical sprays. Picking affected fruit, and 

 bandaging. 



