This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Within the past fifteen or twenty years commercial gardeners have taken a much keener interest in the various diseases and pests that prey upon their crops than their predecessors did. During that period great changes have taken place in cultural conditions, and all crops are now grown not only in larger quantities and on a more extensive scale, but in many cases under what may be called an "express" or "intensive" system. Every grower wishes to be first in the market, so as to secure the highest price; and this very craze to be first with everything has brought about insensibly and gradually changes in the constitution in the various kinds of plants grown for market purposes. At one period of the year they are forced or rushed into growth in great heat; at another they are retarded or kept in check in a freezing atmosphere; while in other cases, where neither forcing nor retarding is employed, some crops are so drenched with chemical manures that it is not at all surprising that some of them become so soft and tender in tissue as to fall an easy prey to fungoid diseases and to insect attack.
No crop is now immune from attack, and this knowledge keeps the commercial gardener constantly in a state of fear and apprehension. To add to his troubles, some diseases, notably the American Gooseberry Mildew, have been scheduled by the Board of Agriculture and Fisheries, and a grower having any bushes affected with this disease is liable to heavy penalties unless he reports the same. In some cases indeed, where the orders of the Board of Agriculture have been treated lightly, some market gardeners have been fined as much as £50.
Attacked by insect enemies and fungoid diseases on all sides, the market grower has called in the aid of the entomologist on the one hand and the chemist on the other, and has spent much money in experimenting with various remedies that have been recommended either to check his enemies or get rid of them altogether. The entomologist has assumed a prominent position in describing the habits and marriage customs of the various insects that are a plague to the gardener. And the mycologist or fungologist tells of the wonders he has discovered through the microscopic lens about the various fungi that make themselves unwelcomely at home on the roots, stems, leaves, flowers, and fruits of various crops.
With the aid of the mycologist, the entomologist, and the chemist, telling him what to do under every conceivable method of attack, the commercial gardener ought to be pretty well safeguarded by now, and the war he has been carrying on for years on insect and fungoid diseases ought to have decimated the ranks of his foes over and over again. But, alas! it is not so. The various injurious insect pests and fungi appear to be, if anything, in greater force than ever, and they infest our crops with as great persistence as in former years.
Enormous sums of money are spent annually in emulsions, mixtures, insecticides, fungicides, and poisonous nostrums of all sorts, in addition to grease bands, smudging materials, &c; and the trade in these remedies seems to be getting larger instead of smaller. One would imagine that, if the various anti-pest remedies on the market possessed any efficacy at all, there should be very few insects left, and the trade in the remedies would naturally contract instead of expand. One must, of course, recognize that commercial growers are taking a keener interest in the diseases afflicting their crops than they used to, and this would account in a measure for the vast quantities of insecticides and fungicides that have been used of late years. The hard fact, however, remains, that there seems to be no diminution in either the numbers or attacks of the grower's persistent foes; and this indicates the impotency rather than the destructive power of the remedies.
While not wishing to minimize the value of the various insecticides and fungicides on the market, the writer is of the opinion that they are not always used to the best advantage and at times when they would be most likely to perform the work expected from them. Owing to the different natures and periods of destruction of the various insect pests and diseases, it is essential that different remedies must be adopted at the times when they are likely to prove effective.
Taking the insect pests first, they may be roughly divided into (1) pests under glass, and (2) pests in the open air.