PLANT DISEASES. 



739 



with dilute Bordeaux mixture when the leaves are expanding, and 

 repeated at intervals of ten days if the fungus is observed. 



V. — Watering, Spraying, Mulching, Pruning. 



The title of this discourse will probably suggest the idea that new 

 methods of carrying out the routine work of the gardener are to be 

 ventilated. This, however, will not be the case, and, except incidentally 

 here and there, my remarks will be confined to suggesting the possible 

 danger of introducing or facilitating the spread of disease, through lack 

 of knowledge, in the act of watering, pruning, &c. 



To commence with watering. As a rule, too much water is used, 

 especially in houses, and unless ventilation is very carefully attended to 

 the foliage remains damp too long, and floating spores settling on such 

 leaves germinate readily. Now if such spores happen to belong to 

 Botrytis, or other parasitic fungi that can pierce the cuticle of the leaf 

 or enter through its stomata, there is the possibility of infection. Where 

 open tanks for water are present in a house, such water contains numerous 

 spores of various kinds, many of which are in active germination. When 

 such water is used for syringing, many spores are by this means deposited 

 on the leaves. This is more especially true when the water is collected 

 from roofs. In one such instance it is certain that the Chrysanthemum 

 Rust was introduced into a house by spores carried into a tank from out- 

 side, and spread on to the plants by spraying. It sometimes happens 

 that a single plant in a house is slightly diseased and overlooked, and by 

 syringing, the spores from this one plant are spread, and an epidemic may 

 be started. 



In addition to fungus spores, open tanks, unless very frequently 

 thoroughly cleaned out, contain a large number of moss and algal spores, 

 and the dense green matted growth on the soil in plant-pots is the out- 

 come of using such water. How many seedlings in pots have been 

 suffocated by this felt of moss and alg» gardeners alone can tell. 



So far as the watering of seeds sown in pots is concerned, if water 

 were used that had been recently boiled, no moss or alga would appear. 

 This small amount of extra trouble would well repay, and need only 

 be continued until the seedlings were well established. 



A quart of deep rose-coloured solution of permanganate of potash 

 mixed with the water in a tank once a week would greatly aid in destroy- 

 ing fungus moss or algal spores when germinating, and would also pre 

 vent to a great extent the germination of spores on the leaves. The 

 only objection to this method is the fact that this substance, in 

 common with potassium sulphide, discolours white or light-coloured 

 paint. 



Spraying is such an important matter, requiring experimental 

 work to be of any real value, that it can only be touched upon in the 

 present lecture. There is much misconception as to the object and value 

 of spraying. It is important to remember that spraying is purely pre- 

 ventive work, and will not cure a disease ; but if properly done, and at a 

 sufficiently early stage, it will check the spread of an epidemic. Success 

 in spraying depends mainly on the apparatus used ; the nozzle should be 



I 2 



