DISCOVERY 



131 



" blight year" amongst the potatoes, and it is not 

 unusual for farmers in such a year to lose at least 

 half, if not more of their crop. WTiat this means in 

 figures can be calculated by considering the acreage 

 of potatoes only in 1920. This is reported as 544,000 

 acres, and the crop should average out at 5,440,000 

 tons at the rate of 10 tons the acre. In all probability 

 it will be somewhere approaching 3,264,000 tons, 

 which is at the rate of 6 tons per acre, the average 

 crop usually grown in England. Much of the loss is 

 due to preventable causes. 



In America, the land of big figures, the Codling 

 Moth (the parent of the maggot in apples) is stated to 

 cause an annual loss of nearly 2,500,000 tons, and the 

 Cotton Boll Weevil costs Texas cotton-growers over 

 £5,000,000 annuall}'. A wilt ^ of tomatoes caused a 

 loss of 50 per cent, of the crop in one State, while 

 the loss in other States varied from 10,000 to 25,000 

 tons. Here future losses may be checked, as a wilt- 

 proof tomato plant has been obtained. In the Laredo 

 district of Texas a tiny " fly," known as a " Thrips," 

 reduced the tonnage of onions which were exported 

 by 20 percent., and in Kansas in 1916 it was estimated 

 that 250,000 acres of oats and 100,000 acres of wheat 

 were destroyed by the " green bug." Even greater 

 losses were sustained in Oklahoma, and it is added 

 that " a good part of this infestation could have been 

 prevented by a proper entomological procedure." 



There is another side to the picture. The univer- 

 sities of California, as a result of work on a caterpillar 

 pest of the peach, produced in one year an increase 

 of 500 car loads of peaches, and from Holland comes 

 the statement that as a result of the general use of 

 grease-banding to control the winter moths, as men- 

 tioned above, /io,ooo is put annually into the pockets 

 of the Dutch fruit-growers. It is very difficult to get 

 at the cost of checking pests, but a case from California 

 is quoted where a severe attack of caterpillar was 

 found on grapes. Here the system, which consisted 

 of spraying the vines with arsenate of lead and nicotine, 

 was applied for seventeen days, and the cost of 

 materials, labour, and apparatus was £2,200. This 

 was less than 4 per cent, of the net return, as the 

 crop which was saved was estimated by the owner 

 as being worth £60,000. 



It is therefore obvious from such figures (and many 

 more could be enumerated) that there is great scope 

 for preventive measures in the growing of crops, 

 although there is little hope of ever getting the full 

 theoretical crop from any plant, because the cure of 

 one disease frequently gives another disease or pest 

 an opportunity of establishing itself. Still, by general 

 hygienic methods many plants would be saved to 

 provide food which otherwise would be wasted. 

 1 The withering and death, of a plant. 



The word " Hygienic " connotes cleanliness, and 

 townsmen, with visions of a farmyard and its frequently 

 unsavoury contents, wonder where it comes in. In 

 this connection, however, it means the general tidiness 

 of fields and plantations, and the disposal of refuse 

 therefrom. Quite a large proportion of the pests of 

 the growers have to find a resting- or hiding-place from 

 one season to another, or until the time when their 

 particular fancy in the way of sustenance again grows 

 on the field where they are. Their opportunity arises 

 when the grower leaves the refuse of the crop lying 

 about, whether it be on a farm, garden, or fruit 

 plantation. On this the pest remains sometimes 

 merely hiding, but more often in a resting stage, such 

 as the pupa of an insect or the resting-spore of a 

 fungus. Thus stubble will contain thousands of 

 pupje of tiny fhes, which will ultimately be ready to 

 attack a similar crop in the same field or one near-by. 

 It is to obviate this that the farmers seldom follow a 

 crop by a similar one in or near the same field (rotation 

 of crops). It is, however, apparent that if the farmer 

 could collect up and burn his stubble, he would burn 

 up also its many thousand unwanted guests. In 

 practice this is not deemed possible, and the usual 

 alternative is to plough in and bury the stubble 

 deeply so that flies cannot make their way out of 

 the ground. This, however, is far from being effective. 

 Fruit-growers for the same reasons should cut out 

 the dead and dying wood from their trees and burn 

 it promptly, for it is on this that many of their enemies 

 breed. Thus one disease of plums, known, because it 

 causes the leaves to become silvery, as " Silver Leaf," 

 propagates itself only on dead wood. Consequently, 

 the removal and burning of such wood is a hygienic 

 method of protection, and this is now compulsory, 

 plum-growers being required under a penalty to 

 remove all dead wood each year before April i. 



Many diseases of plants, especially of root vegetables 

 and potatoes, are caused by fungi,' which spend their 

 resting-period in the soil. Here, again, the leaving of 

 vegetables infected by such diseases to rot on the 

 ground means the releasing of thousands, nay, in some 

 cases, millions, of spores into the soil to await the 

 arrival of a fresh crop in a succeeding year. And 

 wait, they will, in some instances for ten years or 

 more. Sometimes such vegetables as infected turnips, 

 potatoes, etc., are fed raw to animals so that they 

 shall not be wasted— only to get back to the land, 

 and frequently to a clean field, with the manure, for 

 the spores pass through the animals unchanged. 



Numsrous similar examples could be given, all 



' A lowly group of plants, of which the moulds on moist 

 bread, cheese, jam, etc., are examples, and which propagate 

 themselves by minute bodies called spores, which act like 

 seeds. 



