Garden Diseases and Disorders

Mildew

The first symptom of this disease is that the young growths take on a reddish tinge and start to curl; then as the disease develops they become covered with a whitish powder. Fortunately this early stage is easily corrected. An effective spray is ordinary washing-soda at the rate of 1 ounce to 1 gallon of water, or alternatively the whitish covering can be sponged away with a little warm water. It is important to tackle it early, as if neglected it will get progressively worse, spreading from the foliage to the flowers and stems, spoiling the first and distorting the second. A bad attack will also be carried through the winter months on the stems, completely spoiling the following season’s growth and flowering. When this occurs the only thing that can be done is to prune hard in the spring so cutting away the diseased wood. Afterwards the new growth should be closely watched and sprayed at the first sign of recurrence of the disease. A copper white-oil emulsion spray is preferable in bad attacks to the washing-soda solution.

There is no doubt the disease is due to unfavourable weather, hot days followed by cold nights being most conducive to the disease, but poor cultivation, dryness of the roots of the trees, draughty situations and closed-in gardens where the air is stagnant also contribute to its development. The weather conditions referred to are common in the autumn, and as a result it is then that the roses are most often attacked. The tendency is to ignore it so late in the season, but it is not wise to do so, and, after all, washing-soda is inexpensive!

Rust

This is probably the most dangerous of all rose diseases. It first appears in the spring, but to the unscientific eye it is not recognizable until early summer, when it takes the form of individual reddish-orange patches resembling mustard, on the underside of the leaves. These spores turn blackish in the autumn. The disease very quickly spreads from the foliage to the stems, causing canker of the stems and early defoliation. Spray immediately at the first appearance of the disease with copper white-oil emulsion, repeating every ten days until the trouble is cleared up. Take care to see the spray reaches the fungus on the undersides of the leaves.

As a precautionary measure against recurrence of the disease the following year, in the autumn collect all fallen leaves and those remaining on the plant and burn them. Also cut out any cankered stems. Spray in January with copper sulphate at the rate of 1 ounce to a gallon of water, taking care to saturate well both trees and surrounding soil. As the disease is contagious, it is advisable, if only an odd tree is affected, to dig it up and burn it.

A further precaution against recurrence is to cover the rose-beds in the summer with an organic dressing. The value of this is three-fold: it will provide nourishment, protect the roots from the heat of the sun, and act as a buffer between any spores that may be in the soil on diseased foliage from being splashed up on to the trees and starting re-infection. Peat, compost, dung, leaf-mould or grass mowings can be used, either separately or mixed, at a depth not exceeding 2 inches, and it can be maintained at this level throughout the summer with additional grass mowings.

Black Spot

This is very common, but fortunately rarely fatal if measures are taken to mitigate its effects.

The first signs are minute black spots on the leaves.

Unless these are checked in their early stage, they rapidly enlarge until each leaf has its entire nutriment absorbed, when it yellows and falls from the tree. Normally the disease does not appear until August or September, but trying weather conditions can cause an earlier attack. Cold winds in late May or early June which upset the normal function of the foliage render it susceptible to the disease, and if hot, wet weather is then experienced an attack is very possible. The use of a colloidal copper spray when the spots first appear will prevent the disease spreading, but if defoliation should occur syringeing with clean water in lieu of the spray is likely to have better results. Apply at the same time a handful of Epsom salt (magnesium sulphate) round the roots of each affected tree and water it in. The salts will help to promote the formation of new foliage.

The harmful effect of the premature defoliation is that the stems without foliage fail to ripen, and are therefore unable to withstand the hard winter weather. The full programme of treatment to offset the unripeness of the wood and to prevent a recurrence of the disease the following year is as follows:

In September apply to the beds a dressing of sulphate of potash at the rate of 3 ounces to the square yard.

In December prune the trees, cutting away all twiggy growth and shortening the long shoots. Strip the trees of any remaining foliage and collect as much as possible of that which has fallen and burn it.

In January spray the trees with copper sulphate at the rate of 1 ounce to 1 gallon of water, saturating the surrounding soil as well as the trees.

In March complete the pruning, cutting away all wood that has died back and any that is obviously soft.

In April apply a dressing of organic manure.

During the rest of the season, maintain the top dressing as described for rust.

It should be noted, however, that all discoloration of leaves is not caused by black spot; it is very often attributable to other causes, such as mineral deficiencies, cold winds or scorch, the latter due to the action of the sun on wet patches on the leaves. The best advice regarding black spot, should there be any doubt, is first to get it confirmed by a reliable source before starting to spray.

Chlorosis

There are several types of chlorosis, but the one common to roses is lime chlorosis, due to an excess of lime in the soil. The leaves gradually lose their green colour and become a sickly yellow, the yellowing usually beginning between the veins. Occasionally some parts of the leaves remain green, and a speckled appearance results.

As it is known that loss of chlorophyll is due to a deficiency of iron, the treatment recommended is the adding of sulphate of iron to the soil at the rate of 1 ounce for each plant. Apply it as crystals about the size of a pea, and lightly prick it in about the roots. Spraying with a solution of 1 ounce of iron sulphate to 1 gallon of water also turns the leaves green, and it is a good plan to combine the two methods.

Pedicel Necrosis

Rotting of blooms on the plant occurs fairly frequently. It can be caused by thrips, or is due to the fact that some full-petalled varieties are apt to ball in a wet season. If the rotting, however, is accompanied by a blackening of the neck of the flower stem, it is fairly certain that the trouble is a physiological one due to a soil deficiency. The most likely deficiency is potassium, and a dressing of sulphate of potash at the rate of 2 ounces to the square yard should rectify matters. Work the potash into the soil, taking care not to disturb the roots of the plants. To hasten recovery spray affected plants every ten days during the growing season with a solution of sulphate of potash at the rate of 1-1/2 ounces to 1 gallon of water until the trouble disappears.

02. May 2017 by admin
Categories: Featured Articles, Pests and Disease, Plants, Shrubs, Trees, Weed & Pest Control | Tags: , , , , , , , , , , , , , , , | Comments Off on Garden Diseases and Disorders

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