# The Amateur's Greenhouse and Conservatory/Chapter 24

CHAPTER XXIV.
GREENHOUSE VERMIN.
The insects which infest the plants usually grown in the greenhouse are few in number, but capable of doing an immense amount of mischief if not kept under with a strong hand.
Those which occasion the most trouble are green-fly, black fly, thrips, red-spider, and scale. They are all more or less destructive, and when once they obtain a firm footing in the house are very difficult to eradicate. The first three are, perhaps, the most easily disposed of, as they can be effectually destroyed with tobacco-smoke, or by immersing the plants in tobacco-water. The other two are the most persistent, and a considerable amount of labour and perseverance will be found necessary, as they cannot be dispersed with tobacco-smoke. First of all, it is necessary to consider what the most favourable conditions are for the development of these pests, and these may be said to consist in a dry and confined atmosphere, and an unhealthy state of the plants, especially when brought about by neglect in watering. In fact, it is the easiest matter possible to produce a swarm of green-fly, or to have the foliage of the plants smothered with red-spider, for it is simply necessary to neglect the air-giving and watering for a few days to ensure either of these results. Allow the ventilators to remain closed for two or three hours every day after they should be opened, and insufficiently supply the plants with water, and the cultivator will soon be supplied with sufficient work to employ his head and his hands, and, moreover, tax his patience, for, probably, the remaining part of the season. The opposite of these conditions will, it may be readily imagined, promote a vigorous growth, and check the development of these pests. With a careful system of watering and proper attention to air-givmg, there will not be much trouble with either green-fly or red spider. The keeping ​of unhealthy plants is one of the chief sources of the vexatious mischief done in the greenhouse; and if the amateur would have the moral courage to utterly destroy all plants as soon as they are out of condition there would not be one half the trouble in keeping the occupants of the greenhouse clean. Therefore, if a plant has from any cause become unhealthy, throw it away to make room for others, and thus prevent its being the means of spreading destruction on all sides.
Fumigating with tobacco-paper or tobacco itself is the grand remedy for green and black fly and thrips, but, as it may not always be desirable to fumigate the house, dipping must in some cases be resorted to. Tobacco-paper is cheaper than tobacco, and the cheapest and most powerful tobacco is common shag. A quarter of a pound will suffice to fumigate a medium-sized structure. In using tobacco-paper, it must be made moderately moist; when quite dry, it will burst into a flame and scorch the foliage, but if made too moist it will generate steam, and not be so effective as it otherwise would be. In the preparation of the paper, pull it into small pieces, and separate all that is pressed together singly, and then sprinkle it with water if it requiries moistening. There are several forms of fumigators, but the best is Dresehler’s, for by its means the houses can be filled with smoke from the outside. Appleby’s is a simple contrivance, but it does not appear to present any material advantages over the common flower pot, excepting that it is more easily moved about, and not liable to be split with the heat. When a flower pot is used, knock a hole in the side, about an inch from the bottom, and place a few glowing cinders in the bottom; upon these sprinkle a handful of dry brown paper, then a handful of dry tobacco-paper, and when it bursts into a flame commence to fill the pot with the moistened papers, and take it into the house, and blow it steadily to get it fairly lighted. The grand point is to make a good start, for it will then burn freely without much further attention, and render it quite unnecessary to remain in the house the whole of the time. A sharp look-out must be maintained from the outside, and if it shows signs of bursting into a flame stir up the unconsumed materials and damp it slightly; add fresh if the house is only partly filled with smoke. In practice it will be found more desirable to keep the paper burning briskly until the house is filled, and ​then take the pot out of the house, and remove the unconsumed portion; for when it is allowed to burn nearly out, and then left in the house to smoulder, there is a danger of a portion of the paper becoming quite dry, and then bursting into a flame. In using Dreschler’s fumigator the paper must be ignited in exactly the same manner as in the flower pot, and until it is fairly alight turn the handle connected with the cage rather quickly, but afterwards it must be turned slowly.
Let the foliage of all plants be quite dry when fumigated, for when moist it is invariably more or less injured by the smoke. The evening of a still day is the most suitable for the work, as the house can remain closed for at least twelve hours afterwards. All openings must be closed, and the roofs of small structures and pits covered with mats or canvas, to prevent the too rapid escape o£ the smoke. Usually two fumigations with an interval of one or two days between will suffice, but when the plants are badly infested with thrips it will be necessary to fumigate three times on alternate days. In the morning after the house has been fumigated give the plants a thorough syringing to wash off the dead insects, and to finish off those in a dying state. As the smoke will destroy the flowers in a wholesale manner, all plants in bloom which it is desired to preserve must be removed.
Dipping.—Clear water is the most valuable insecticide, for when the plants are syringed freely during the growing season there will not be much danger of their being infested with green-fly or any other pests. Hot water is remarkably efficacious, and any soft plant may be dipped into water heated to 120° Fahr., while plants of harder texture may be dipped in water at 140°. Gisburst compound, prepared according to the patentee’s directions, is perhaps one of the most effectual and the cheapest of the preparations. Tobacco-water, which can be made by steeping good shag tobacco in boiling water for a few hours, is efficacious and easily made. A little size mixed with any of the liquid mixtures will ensure its adhering to the foliage, and it will do no harm if the plants are thoroughly syringed the following day. Large plants must be syringed, but for those of small or medium size sufficient should be made to admit of their being immersed, for every portion of the foliage will then be thoroughly moistened, and all real waste prevented, provided, of coarse, the plants are held over the ​dipping tub a short time. Quassia chips steeped in water, at the rate of two ounces to the gallon, make a most effectual liquid for destroying green and black fly. Large-leaved plants badly infested with thrips or red spider will require sponging with either Gishurst compound or tobacco-water. It will be tedious work, but unless it is done effectually it would be better to destroy the plants instead of leaving them to form a rendezvous for the pests with which they are infested.
DRENCHING BOARD FOR CLEANSING PLANTS.
The subjoined figure of a drenching board, will suggest a simple means of economising any liquid preparation employed for cleansing plants. The plant is laid on the board, and the syringe is used with some force upon it, and a pail being placed in front, a considerable proportion of the fluid is caught for further use and none of it is conveyed to the roots. A carpenter would make such a board for ten shillings or less.
Tobacco-powder is one of the best remedies for green-fly and black-fly, if applied in a proper manner. First of all, stand the plants to which the powder is to be applied on one side by themselves, sprinkle them with water, and dust the foliage liberally with the powder. The puff’s sold by the trade ​ are most useful, for with their aid the powder can be applied to the under side of the leaves more readily. The powder will injure the foliage if left on too long; twenty-four hours will, as a rule, be found the proper time for it to remain, and at the end of that period wash it off with the syringe and clear water, and in a few days afterwards dust the foliage again, if the first application has not been sufficient to annihilate the fly.