If they are discovered before multiplying to any great extent, exterminate them with a fine brush or feather dipped in alcohol, coal-oil or kerosene, any of which, if applied directly to them, will kill them on the spot.
Scale. The scales infesting house plants are of two kinds. The more common is the brown scale, which has a hard, slightly convex, circular shell, one-quarter of an inch or so in diameter. The white scale is much smaller, and soon forms quite dense colonies. Both attack the thick-leaved, smooth-barked plants, such as palms, ferns, lemons, and abutilons. They do not appear to be doing any damage, but invisibly suck the juices of the plant. They should be destroyed at once. This is accomplished by the use of fir-tree-oil soap, whale-oil soap, or kerosene emulsion and a stiff brush.
Thrips. These do not often appear in the house, but may where plants are crowded in a shady place. They eat the substance of the leaves, leaving only the skeleton structure. They are small, about a quarter of an inch long, and brown or black. Aphine, kerosene emulsion or Paris green (one teaspoonful to twelve quarts of water) will keep them quiet.
Root Aphis. Sometimes the leaves of a healthy plant will begin to look sickly with no apparent cause. It may be found upon examination that the blue root aphis is at work, clinging in clusters to the rootlets. Remove and wash away the soil, and then wash the roots in whale-oil soap suds, and repot in fresh soil. If no fresh soil is available, tobacco tea or tobacco dust should be washed into the soil every other day for a week.
Soil Worms. The common earthworms sometimes find their way into a pot, and while they do not seem to bother the roots, I should judge from observation that they render the soil next to useless, especially in small pots. Another worm, or rather larva, sometimes to be found, is very small and hatches into a small white fly. If numerous, they do a good deal of damage. The treatment recommended for root aphis will get rid of them; or lime water (slake a piece of fresh lime the size of an apple in a pail of water, drawing off the water after settling), if used freely will kill them.
DISEASES
There are but two plant diseases likely to attack plants in the house: fungus and mildew. The first seems to be a sort of decomposition of the leaf, leaving a black, powdery residue. It is combated by spraying with bordeaux. Bordeaux can now be had in paste or powder form, which for small quantities is much better than to try to mix it yourself.
Mildew causes the tenderest leaves to curl up and some of them seem to be covered with a white powder. Flowers of sulphur, dusted over the plants while the foliage is damp, is the standard remedy.
For the sake of ready reference, the foregoing is condensed in the following simple table of plant insects and diseases.
======================================================================= INSECT | CONDITIONS | OR | SUPPORTING | REMEDIES DISEASE | GROWTH | —————————-+———————————+—————————————— Aphis, green and | Shade; poor | Aphine; tobacco-dust black | ventilation; | or tea; kerosene | thick foliage | emulsion; hot | | water bath; insect | | powder. | | Aphis, blue | Stunted growth; | Whale-oil soap | lack of water | solution; repotting; | | tobacco tea applied to | | roots. | | Thrips, 1/4 inch, | Shaded places; | Kerosene emulsion; long, brown or | crowded plants | Paris green—1 black; they eat. | | teaspoon to 12 quarts Mealy bugs } | | water. Other scale } | Corners; close, | Brush off; coal-oil; insects } | dry air | kerosene emulsion; | | hot water. | | Red spider | Hot, dry | Moisture, sulphur, | atmosphere | hot water. | | Rose-beetle | | Hand picking; wood | | ashes. | | White flies | Dry foliage | Kerosene emulsion. (Aleyrodes) | | | | | | Slugs | Dark corners; | Air-slaked lime. | dampness; | sweetened bran and | decaying wood | Paris green. | | Ants | | Insect powder; | | molasses traps. | | Angleworms | Dampness; heavy | Lime; lime-water; | soil | tobacco tea, and | | tobacco dust washed | | into soil. | | | | White grub | Manure not old | | enough. Destroy. | | | Fungous leaf spot | Shocks; checks | Bordeaux; Fungine. | | Mildew | Checks | Flowers of sulphur; | | Fungine. =======================================================================