130 



DISCOVERY 



subject to an attack of bli^lit, if it were in such an 

 amount as to darken the air. The east wind also 

 gets credit for bringing " Wight," and this is no new 

 idea. Witness the blasting of the cars by the east 

 wind in Pharaoh's dream. 



When, however, some knowledge of the life-history 

 of the various pests and diseases found on plants 

 was obtained, attempts were made to check at least 

 the damage done. At an early date various poisons 

 were used as insecticides, such as solutions made by 

 soaking tobacco or by dissolving soap, and the 

 accidental discovery of " Bordelaise " gave an impetus 

 to spraying generally. 



Bordelaise, or Bordeaux mixture, as is well known, 

 was first used to cover grapes growing alongside paths 

 and roads to prevent " finger blight." It was dis- 

 covered, however, that vines treated in such a way 

 were free from attacks of mildew, and the habit of 

 spraying the whole of the vineyards with this mixture 

 of blue vitriol and lime became general. Later it was 

 found that it not only prevented attacks of mildew 

 on vines, but many other diseases caused by fungi 

 on plants generally. Nowadays it is commonly used 

 to prevent attacks of ordinary potato disease 

 (Phytophthora). 



With the increase of spraying, came the develop- 

 ment of spraying machines for distributing the fluids, 

 originally put on in a primitive way by sprinkling it 

 on the plants with a brush of twigs. Nowadays a 

 big industry has sprung up, and all kinds of machines, 

 from small hand-pumps suitable for an amateur's 

 greenhouse, to large complex motor-tackle for use on 

 farms, are produced. In addition, numerous firms 

 have specialised in the providing of suitable sprays 

 and washes, and other material connected with the 

 checking of plant pests. 



Old growers frequently say that there were not so 

 many pests in their young days. As a matter of fact, 

 most of the pests abundant at the present- time were 

 present, but not in sufficient numbers to attract the 

 ordinary growers' notice. On the other hand, there 

 has been an increase in the opportunity for the spread- 

 ing of such pests. Half a century ago, orchards were 

 scattered and few in number. Since then, especially 

 in certain districts such -as Kent, Wisbech, and 

 Worcestershire, the planting of fruit trees has gone 

 on to such an extent that orchard meets orchard for 

 miles, while plants have been collected from all 

 countries. It is, therefore, not surprising that pests 

 which were confined to isolated districts, with a limited 

 amount of food material, made the most of their 

 opportunity. The great increase of food plants 

 enabled them to perpetuate themselves on a large 

 scale. Coincident with this, nurserymen and others 

 have introduced plants from abroad with their respec- 



tive pests, and in many cases the pest has not been 

 content to remain on its original food plant, but has 

 adapted itself to other varieties, so that new pests 

 on our native plants have been introduced. In some 

 instances, good examples being American gooseberry 

 mildew and wart disease of potatoes, these pests have 

 made the industry a precarious one, and great losses 

 have been incurred. 



Growers on a commercial scale have been passing 

 through a period where pests were unheeded until 

 obvious damage was done, and have then attempted 

 to check or kill the pest by spraying. The latter will 

 still be necessary, but nowadays efforts are being made 

 to lessen the labour involved by a little forethought 

 on the part of the grower. He is finding that it pays 

 him to learn the life-history and appearance of the 

 enemies of his crops, so that he can not only recognise 

 them at an early stage in their existence, but also 

 know the most vulnerable point in their life-history. 

 Such knowledge tells him that general untidiness and 

 carelessness in the orchard and field means the propa- 

 gation and protection of his enemies. Hence the 

 science of Plant Hygiene is coming into being. " Pre- 

 vention is better than cure " applies here as elsewhere. 



As an example of the help given by a knowledge of 

 the life-history of a pest, that of the winter moths 

 might be quoted. These moths, as their names 

 imply, are in the moth or adult stage during the winter 

 months, and they are singular in having females which 

 are wingless, or practically so, and which therefore 

 cannot fly. In order to lay their eggs they have to 

 climb up the trees, and most trees are a prey for them. 

 Up-to-date growers take advantage of this stage to 

 place around the trunks of the trees a band of parch- 

 ment paper on which a thick and sticky grease is 

 placed. If properly done, the moth is unable to pass 

 over the band, and is caught there. Each moth would 

 lay from two to three hundred eggs, a large proportion 

 of which would hatch out to the famihar green cater- 

 pillars that so frequently eat the trees bare in the 

 spring and early summer. Where this grease banding 

 is not done, the alternative is to allow the moths to 

 lay their eggs. These hatch in due course, and the 

 trees are then sprayed with a poisonous wash in the 

 spring, so that in eating the leaves the caterpillars 

 also partake of their share of the poison, which is 

 usually arsenate of lead. 



The necessity for dealing with pests cither by the 

 method of prevention or of cure is realised when one 

 considers the amount of damage such pests can do to 

 the food supply of the country, and it is no exaggera- 

 tion to state that on an average, approximately one- 

 tenth of every crop is lost annually through one or 

 more diseases or pests. Frequently this percentage 

 rises considerably, for example, when one gets a 



