DISEASES of plants are many and varied, some being the result of attacks of injurious insects, while others are caused by fungus growth which comes from improper nutrition and poor circulation or from very sudden atmospheric changes: - for example, from warm, balmy weather which encourages rapid growth, to cold, harsh winds which seem to chill the whole plant while checking its growth. The plant in these conditions suffers particularly from the fact that, on account of the soil being warm, the roots continue sending up supplies of sap of greater quantity than the leaves and soft stems (being so chilled and semi-paralyzed by the cold air) are able to assimilate, and thus there is caused a choking of the sap-vessels which greatly weakens the plant, so that it gets into a condition susceptible to an attack by any disease. Unless the weather moderates so that the plant can again make vigorous growth and throw off the attack, it may suffer severely and take weeks and sometimes even months to recover.
The most common of the fungus diseases is undoubtedly the Powdery Mildew which attacks leaves, stems, flowers and fruits. It appears like a thin white powder at first over the leaves, afterwards spreading to the stems, stopping at once and entirely the further growth of the part attacked. It is propagated by spores which increase with amazing rapidity, often dwarfing and sometimes killing outright the whole plant. There are several kinds of Mildew including the Rose Mildew, the Grape Vine Mildew the Hop Mildew, the Pear Mildew, etc. All varieties of Mildew may be checked by dusting flowers of sulphur over the affected and the adjoining parts of the plant.
As soon as the least speck of Mildew is noticed on any part of the plant, the affected part should at once be given a good dusting, and this work should not be delayed an hour longer than is necessary, otherwise serious damage will be the result: - for example, if the plant attacked is a Rose, the Mildew, if not checked, will ruin the crop of flowers.
Bordeaux Mixture is also a good cure for Mildew, and may be used if sulphur should fail. It should be applied in the same manner as sulphur.
A sulphur bellows made especially for use in this work may be procured from any seedsman at little cost, and it will be found that the use of the bellows economizes the sulphur.
Green Flies (Aphides), sometimes called Plant Lice, are very destructive to the young shoots and foliage of plants, especially Roses on which they congregate in large numbers and send their long sharp feelers into the bark and leaves, sucking the juice from the plants. As they multiply with astonishing rapidity, they, if not destroyed, will eventually cause the destruction of the parts affected, and this in a very short time.
The best remedies for successfully getting rid of these pests are Tobacco and Whale-oil Soap; even common soap-suds, when not too strongly impregnated with soda or chloride of lime, will be found effective for this purpose if the foliage is syringed freely in the evening and sprayed with clear water through the hose the following morning. This should be done three consecutive evenings.
To apply the tobacco, one pound of the common tobacco-leaf should be first soaked in six gallons of hot water to which should be added one-half pound of soft black or whale-oil soap. These should be mixed together by the syringe, and the plant should be thoroughly syringed with the liquid in the evenings and washed by the hose with clear water early the following mornings.
Sometimes it is not desirable to use tobacco in liquid form. In that case the leaves can be dusted freely with tobacco dust which should be left on the foliage for about forty-eight hours, and then washed off with the hose. Should the first application be not effective, a second or even a third application can be made until all the flies are cleared off.
Several prepared mixtures are sold by seedsmen, such as Gis-hurst's Compound, Fir-tree oil, etc., which, if applied as directed on the labels, will be found effective. Often water used freely with the hose under good pressure will clean them off if applied before the flies have got too strong a hold on the plant.
There are other kinds of Aphides some of which are black and attack Cherry and other fruit trees, but they generally yield to the same treatment.
When the Aphides attack plants in a green-house, fumigation with tobacco stems will be found the best remedy. A close, dull evening should be selected and the foliage of the plants should be perfectly dry.
To effectively fumigate a green-house it is necessary to get an iron pot into which should be put a few pieces of lighted charcoal, on which should be spread a few tobacco stems. On top of the tobacco a layer of damp moss should be placed, and the house should be densely filled with the smoke, care being taken that no flame arises in the burning. The house must be kept perfectly closed for twelve hours. Then the ventilator should be opened and the plants syringed freely with clean, tepid water. Should the first smoking not be effective, the operation can be repeated a second evening in the same manner, and, when the fly has had a long hold on the plants, it may be necessary to fumigate even a third time.
A pest which is responsible for a great many of our worst failures in plant cultivation is Thrips, as it attacks some of our most delicate and most finely leaved plants, and, from the fact that this insect is so very small, it is generally not noticed until considerable damage has been done.
It feeds only on the juices and fleshy parts of the leaves, leaving the fibrous parts untouched, this giving the plant a withered, blighted appearance.
This insect may be recognized by its narrow, black or brown body, and its four straight narrow wings which are fringed with hairs in saw-like edges. There are several varieties, but as they are all equally destructive and yield to the same treatment, it is unnecessary to further refer to their identification. When the pest is found to be infesting a green-house, the fumigating treatment as recommended for Aphides produces satisfactory results. When the insect is found on shrubs out of doors, the plants should be well syringed with, tobacco water, care also being taken to see that the plants are well watered at the roots, this watering giving additional vigor to the plants which will tend to render the Thrip attack harmless.