Garden Plant Diseases, Soil Diseases and Plant Viruses

Garden Plant Diseases



The most common garden plant diseases are those which affect the foliage, and thus cause a severe check in growth, unsightliness or, in bad attacks, the death of the plant.

It is well known that plants which are of a very soft nature, i.e. over leafy, due to over feeding with nitrogenous fertiliser, are very much more likely to be attacked by fungus troubles than are sturdy, well-grown plants which have received an adequate supply of potash, although the presence of this latter factor will not guarantee immunity.

One of the materials used against fungus diseases of foliage is Bordeaux Mixture. There are several different variations in the make up of this fungicide, but a usual mixture is 8ozs. of copper sulphate and 8ozs. of hydrated lime to 5 gallons of water. The copper sulphate is dissolved in water, in a wooden tub, and the lime in a separate vessel. Add the copper solution to the lime, stirring well. Test with blue litmus paper, and add more lime if the litmus paper turns blue. Strain the mixture and use the same day. One can purchase the necessary ingredients in the same package, in two sections, and here, makers directions should be followed regarding mixing for use.

clematis-leaf-spot Other garden plant diseases which may appear are :


This disease, which can affect chrysanthemum blooms under glass, and cause the petals to “damp” and rot, is very largely due to insufficient ventilation and too damp an atmosphere. The spread of the grey fungus spores can be minimised by cutting off infected blooms and avoiding shaking the spores on to nearby plants. If this trouble appears, keep the atmosphere rather drier and do not wet the foliage whilst watering.

Rust of Antirrhinums

This disease can be serious enough to damage severely the foliage. The symptoms are dark brown spots on the undersides of the leaves. Foliage can be so badly affected that it becomes “scorched” and the plants die off.

Fortunately, where this disease is troublesome, there are now resistant varieties, e.g. Wisely Golden Fleece, which is yellow with a pink flush; Pink Freedom, and Wisely Cheerful, which is also pink. This is the best answer to the problem.

Rust of Chrysanthemums

This may put in an appearance under glass, particularly if plants are not given sufficient ventilation. The chocolate brown spots on the undersides of the leaves cause a severe check to the foliage and the entire plant is weakened. When the plants finish flowering, make sure that no infected leaves are left in the greenhouse, under benches, it pipes or staging, where they might serve as a source of reinfection the following year. Dusting the foliage with yellow sulphur is of some benefit, but aim at growing the plants sturdily, with ample ventilation, and pay close attention to watering.

Rust of Sweet Williams

This garden plant disease is common in the southern counties, and appears as brown spots in the undersides of the leaves. The varieties with dark red flowers and dark foliage are very resistant. Set the plants so that there is a good air circulation between them and aim at sturdy growth.

Soft Rot of Iris

This is not uncommon. The foliage of attacked plants turns yellow at the edges and, later, the rhizomes decay. This disease is worst in wet, heavy soils, especially if drainage is poor. These conditions should be corrected and new plantings, the rhizomes planted shallowly, made on a drier site.


There are several species that attack a fairly wide range of plants. Often mildew is induced by very dry conditions; an example of this is the mildew found on michaelmas daisies. If the plants are well grown, and obtain adequate moisture from compost dressings, little or no trouble is experienced. At the end of the season, make sure that no infected foliage is allowed to remain on the crowns of the plants, should the trouble appear in late summer.

Chrysanthemums under glass can be affected by the trouble, induced by draughts and dry conditions. A light dusting with yellow sulphur on the foliage will help.


Soil Diseases

So far as flowers are concerned, the trouble most frequently met with is “damping off”, which affects small seedlings grown in pots or boxes. Where this method of propagation is employed as under glass, make sure that clean water is used, especially if this is being taken from tubs or tanks.

The use of sterilised soil such as that in John Innes Composts, should ensure freedom from these diseases. On a small scale, one can partially sterilise the seed compost being used by saturating it with boiling water and then allowing it to dry out sufficiently before sowing the seeds concerned.

In severe cases, the boxes or pots can be watered with Cheshunt Compound (1 oz. in 2 gallons of water), but this measure will not cure seedlings already affected. The symptoms of attack are: the rotting of the seedlings, at soil level. Large patches can be affected in a seed tray, resulting in a total loss of plants. Where losses have been experienced with small seedings, coat the surface of the seed mixture with 1/8 in. of fine sand and cover the seed with the same depth. Make sure that too much water is not given and that clean cans are used.

Wilt of Asters

There are two types of wilt disease which affect these plants. One is often called “blackleg” which causes the stems to turn black at soil level and the plants to wilt and die. A heavy soil, especially a heavy, wet soil, will cause serious losses, particularly in a wet season. All infected plants should be pulled out, and asters should not be planted on infected soil for at least 3 or 4 years.

Wilt, caused by a different fungus, gives similar symptoms, but there are now several wilt-resistant varieties available, and full use should be made of these.


Virus Troubles

The two crops most likely to be affected, in each case by more than one virus, are chrysanthemums and dahlias. To describe the symptoms of each would take almost another book but, in general, affected plants become stunted or flowers distorted and so severely checked that they are useless.

It is essential, with both these subjects, to purchase plants from a clean source, so that no virus-infected material is introduced. Do not take cuttings from plants known or suspected to be showing virus symptoms.

Aphides and other sucking insects can spread these troubles by sap transference, as may taking out side shoots from affected plants and carrying infected sap on the fingers to neighbouring subjects.

Virus-infected plants should be removed before further infection can take place. So long as it is certain the material will be well heated up in a properly made compost heap, it can be used for this purpose; if doubt exists, I would prefer to burn such infected material.


09. September 2010 by admin
Categories: Garden Management, Pest Control | Tags: , | Comments Off on Garden Plant Diseases, Soil Diseases and Plant Viruses


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