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Apple-sucker (Psylla_mali).--It has been estimated that the damage to the apple crop in Worcestershire from this cause in one year amounted to seventy per cent.
Wheat-bulb fly (Hylemyia coarctata).-It is calculated that this insect is responsible for the destruction of about one per cent, of the total crop in England and Wales, say, 70,000 quarters.
Frit fly (Oscinella frit).-Destroys not less than ten per cent. of the oat crop in England and Wales, say, 900,000 quarters.
Turnip fleas (Phyllotreta spp.).—In 1881 the Agricultural Committee of the Privy Council computed the loss of root crops due to these beetles in twenty-two English and eleven Scotch counties at over £500,000.
Hop aphis (Phorodon humuli).—The same authority estimated the injury to hops by this aphis in 1882 at over £2,500,000.
Unfortunately, for nearly all the most serious pests no satisfactory statistics are at present available, and the following list, which includes only some of the really important species, in addition to those already mentioned, will indicate how much has yet to be done in this direction.
Cereals: Gout fly (Chlorops tæniopus), wheat midge (Contarinia tritici). Pulse Black aphis (Aphis rumicis), pea and bean weevils (Sitones spp.). thrips (Kakothrips robustus, etc.).
Roots: Aphis rumicis and A. brassica.
Clover Clover weevils (Apion spp.), eelworm (Tylenchus devastatrix). Vegetables Cabbage root fly (Chortophila brassica), onion fly (Hylemyia antiqua), carrot fly (Psila rosa), white butterflies (Pieris spp.), cabbage moth (Mamestra brassica).
Fruit Pear midge (Contarinia pyrinora), apple capsid (Plesiocoris rugicollis), apple-blossom weevil (Anthonomus pomorum), apple aphids (Aphis pomi, etc.), plum aphids (Aphis pruni, etc.), black currant mite (Eriophyes ribis), raspberry beetle (Byturus tomentosus), winter moth (Cheimatobia brūmāta).
General: Wireworms, leather-jackets, chafer grubs, cutworms.
Losses due to Fungus Diseases.
Rust (Puccinia spp.).—In this country the loss from these fungi is assessed at ten per cent. of the crop, thus amounting to nearly 850,000 quarters in 1915 for England and Wales. The three prairie provinces of Canada (Alberta, Saskatchewan, and Manitoba) are stated to have lost 100,000,000 bushels of wheat in 1916 from black In the United States the loss has been estimated at £13,400,000, and in Australia at £2,000,000.
rust.
Barley stripe (Pleospora graminea).-It has been estimated that this widely spread fungus causes a loss of seven-and-a-half per cent. of the barley crop in the north-eastern counties of England.
Potato blight (Phytophthora infestans).—A conservative estimate for this serious disease is ten per cent. of the crop; this works out approximately at 300,000 tons per annum for Ireland and 700,000 tons for Great Britain. The official figure for Germany is £30,000,000 (probably a good deal over-estimated), and for the United States £7,500,000.
Wart disease and corky scab (Synchytrium and Spongospora).-Owing to the presence of these diseases in the United Kingdom the export of potatoes from this country to America (about 300,000 tons), valued at £1,250,000, has been entirely prohibited. In bad cases the former disease may result in a loss of the entire crop and in some places renders the cultivation of potatoes impossible.
Bunt and smut (Tilletia and Ustilago).These cause considerable injury to In Canada the loss is given cereals in this country, but figures are not obtainable. at £3,500,000, and £4,000,000 in the United States.
Brown rot (Monilia spp.).—Attacks, with disastrous results, large acreages of such apples as
Lord Derby," the principal variety grown on the Weald; from fifty to seventy-five per cent. of the blossom is absolutely destroved.
Apple canker (Nectria ditissima).-This fungus seriously interferes with the commercial cultivation of such good varieties of apples as "Cox's Orange Pippin," "Wellington," etc.
The following general estimates of the damage done to crops of all kinds by insects only are worth noting: --Italy, £40.000,000 Canada, £20,000,000; the State of Wisconsin, £2,750,000 to £8,000,000; the State of Tennessee, £2,000,000.
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As regards fungus diseases, Professor T. B. Wood has quite recently estimated that the world's wheat crop is reduced by thirty per cent. from this cause.
In Great Britain we should probably be well within the mark in assuming that the losses caused by plant diseases and pests amount to ten per cent. of all crops.
It is not contended that the losses cited above can ever be entirely eliminated, but there can be little question that they may, even with our present very limited know- ledge, be materially reduced as a result of well directed and properly co-ordinated effort. That such an effort can be highly successful is shown by the excellent results obtained on the Continent against Phylloxera and in this country in the control of wart disease. The immense sums involved and the increasing importance of the home production of foodstuffs make it hardly necessary to emphasize the necessity for taking effective steps to check this wastage; and there can be little doubt that reasonable expenditure in this direction will be repaid many times over.
In view of the dimensions of the losses which the nation appears to suffer on account of the depredations of insect and fungus pests, the ultimate responsibility This has, indeed, for the control of such pests must clearly rest with the State. been recognized by practically every civilized nation, and while private initiative is often responsible for results of the highest importance, the machinery for the control of plant pests is really dependent on action taken by the State.
So far as this country is concerned, the existing organization for dealing with plant pests came into being as a result of the Development and Roads Improvement The former Acts of 1909, and the Destructive Insects and Pests Act of 1907. resulted in the establishment of machinery for the investigation of pests and for the distribution of knowledge so obtained, while the latter was directed towards the prevention, by administrative measures, of the spread of pests, both foreign and indigenous. The details of this organization can hardly be considered here, but the In the general policy underlying the whole fabric would appear to be as follows first place, investigation and research are not carried out directly by a Government Department, but are delegated to certain independent institutions, universities, and colleges which are subsidized for the purpose. It appears to be matter of prin- ciple that the department concerned the Board of Agriculture-should not under- take scientific research. Secondly, the distribution of knowledge, so far as local problems are concerned, is also carried out by subsidized institutions, while more general questions are dealt with by the Board of Agriculture. Finally, the adminis- tration of Acts of Parliament-the legislative aspect of pest control-though formerly delegated in part to local authorities, is now wholly carried out by the Board of Agriculture.
Obviously, the mainspring of any organization for the control of pests is that section which is devoted to research and investigation; it is impossible to spread knowledge until it has been acquired, or control pests by order unless practical methods have been discovered and proved effective.
The question to be asked, therefore, is whether the present policy as regards An answer to this investigation is alone capable of giving practical results. question can only be obtained by referring to the collective opinion of plant pathologists of many countries, and fortunately such an opinion was placed on This conference was attended by record at a conference held at Rome in 1913. political and scientific representatives from thirty countries, and was called in order to draw up an international convention for preventing the spread of pests by commerce. Countries adhering to the convention were required to fulfil certain obligations with regard to the establishment of an efficient machinery for the control of pests, and, as regards investigation, the minimum requirement considered one or more scientific and technical institu- necessary was the maintenance of tions" for the study of the subject. It was clearly recognized that the scientific institution alone would not bridge the gap between the laboratory and the farm, and that a technical institution was required for this purpose.
The machinery in this country may meet the requirements as regards the scientific institutions-but, unless one institution can fulfil both functions, the technical institution appears to be lacking.
It is therefore suggested that, as regards general policy, the establishment of Success in pest control a technical institution is worthy of serious consideration. depends very largely on overcoming a large number of minor practical difficulties. Broad principles appear as a result of the work at the scientific institutions, but broad principles. are of little direct use to the grower, and a further series of experi- Criticism is ments is required to apply the principles to the needs of the farm.
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