Chapter 13 - Pests And Diseases

Read, ye who run, the awful truth, With which I charge my page...A worm is in the bud.

Dean Reynolds Hole

It is a very curious thing that the indigenous roses of this countryside, when growing naturally in the hedgerows or their usual habitat, act as host plants to very few of the many insects which attack other kinds of tree and plant. For instance, the caterpillars of most of the moths found in this country show a decided preference for the foliage of one plant over another, and many, if deprived of that particular plant, would become extinct unless there was another closely allied plant near at hand. Now, although the rose in its wild state has so few caterpillars feeding on it, it is largely because there are nearly always several members of the rose order near at hand, which they greatly prefer. The hawthorn, sloe and wild plum are hosts to more moth larvae in this country than any other plant, with the possible exception of the oak. It is this which makes our garden roses so vulnerable to attacks from so many of these unwelcome pests. It may be that the unnatural conditions in which our roses are grown has some bearing on why these pests turn up their noses at the rose in the open country, and yet show such relish for the same thing in our garden, for I find that they seem to be quite as happy chewing away at the foliage of the briar stocks as they do on the hybrid types. It is quite possible that most gardens contain other members of the rose order in the form of fruit trees, which are so near to their natural food that they find a change of diet very suitable and a pleasant change.

Pests

The caterpillars of moths I have observed feeding on my roses are as follows: the winter moth, mottled umber, gold tail, buff tip, lackey, grey dagger, and rose tortrix, the last being the only one peculiar to the rose; This and the winter moth are the only ones likely to give serious trouble.

The caterpillar of the winter moth shows a decided preference for standard rose trees, the wingless female carrying out its natural habit of crawling up the stem or trunk of a tree to deposit her eggs in the branches. Dwarf roses are attacked, but not to quite the same extent.

Weather conditions undoubtedly govern the severity of the attack by insect pests. In congenial weather, when the plants are growing strongly without a check, it is rare to be troubled in any way, but let the wind get round to the north-east and all the pests that are peculiar to the rose will be there. This is such a usual happening that many old gardeners believe that the 'blight', that is, greenfly, is airborne from the continent. The fact is that these pests that prey on our garden plants prefer those that are not too healthy and vigorous, in the same way that a rabbit will ignore a fine fresh cabbage but will eat off those that have wilted after transplanting.

Although one is powerless to do anything to alter the weather, it is possible to ensure that the plants are given every inducement to grow well, by affording good soil conditions, and not planting in unsuitable positions. In the rose fields where many thousands of plants are grown for sale it is very noticeable how little trouble there is from the pests and diseases which are so common in the great majority of gardens. The reason is plain. The soil is not over-rich, it has probably not grown a crop of roses for perhaps four or five years, and the plants are all maidens, that is to say, the first growth from the previous year's budding, and also the plants obtain all the sun and air that is possible. Contrast these conditions with those that prevail in the average garden where the soil may have grown roses for a number of years, over-manured, with several old decrepit plants that it would be an act of charity to have consigned to the fire, and a draught may be blowing through the passage between adjoining buildings. These are some of the reasons why, if roses are to be grown, constant warfare must be waged in order to allow the plants to win through.

It is unnecessary for me to enumerate all the pests that are only remotely likely to give trouble, so I shall confine my remarks to those against which it is essential that action should be taken.

Aphides or greenfly

If a census of opinion were taken as to which was the worst pest that those who grow roses had to deal with, I think the result would show that aphis or greenfly is the one. It is very rare for a season to pass even in gardens with the very best conditions, without one having to take some measures to keep it in check. The damage aphides can do is considerable if allowed to go unchecked. I have seen Ramblers almost completely denuded of their flower buds by these pests, and when one realizes that the bodies of hundreds, clustered on a shoot, are made up of the very life-blood of the plant, it is easy to imagine the great harm they do. Fortunately, it is not a very difficult pest to deal with, neither does it stay on the plants for very long, so spraying with one of the many insecticides containing derris, pyrethrum, malathion or nicotine, once a week for two or three weeks should suffice to keep the plants free.

Two of the principal enemies of aphides are the ladybird, both larvae and adult insect, and the common sparrow. At nesting time, when the birds are rearing their offspring, enormous quantities of aphides are collected and taken to the nests, and it has always been a matter of amazement that the structure of the young sparrow could be built up of such frail material.

It is not wise, however, to leave the aphis problem entirely to the sparrows, for they seem to make no attempt at reducing their numbers until they are on the plants in sufficient numbers to warrant the trouble.

Winter moth caterpillars

The caterpillar of the winter moth is the next one of importance in the list of pests. The tiny grubs hatch from the eggs some time in April and in a little while draw the leaves of the plant together for a measure of protection. It is this habit that makes it difficult to observe the grubs until the eaten foliage shows their presence. These grubs, like so many of their kind, feed mostly at night, leaving the protection of their daytime home, and anyone who cares to inspect their plants by night with the aid of a torch, can see them busily engaged in partaking of their main meal. They can then be removed and destroyed but such a procedure would only be effective where the plants are few. In the case of Ramblers or other large plants spraying would have to be carried out.

As a means of keeping the plants free from nearly all the pests that suck and bite, I have found that a pyrethrum insecticide containing DDT is most effective. It can be used at any time of the day and does not harm tender growth or foliage.

Rose tortrix moth

There are two species of rose tortrix, one with a green grub and the other brown. The brown one is the worse pest of the two, since it always attacks the flower buds when they are quite small, sometimes eating them right away. It is not easy to detect their presence until it is noticed that the bud on the end of the plant is not growing as it should. Closer examination will show that the grub is doing its work right at the base. As it is well protected, spraying is not as effective as it might be, but as the grubs are not present in large numbers as a rule, dispatching them by hand-picking is as good as anything.

The species with the green grub rolls the leaves together and feeds hidden from view. It is easy to deal with these grubs by simply giving the rolled leaves a squeeze.

Most of the pests that I have mentioned so far are not likely to give much trouble after the first week in June, with the possible exception of aphis, which sometimes puts in a late appearance and stays longer.

Rose chafer

Of those which are likely to give trouble during the summer the rose chafer and thrips are the worst. The former would appear to be rather local, some districts being free from their attentions. They can be a great nuisance, as they fly from plant to plant eating the petals of the blooms. Spraying with pyrethrum and DDT prevents destruction of the petals, at the same time poisoning the beetles. The spraying will have no ill effect on*the blooms, but as with all spraying it is best undertaken in the evening when the sun has lost some of its power.

Thrips

The damage to roses by thrips is confined to the flowers. These tiny insects, just over one-sixteenth of an inch long, invade the blooms at the time when the sepals divide and show the petals. Once inside they penetrate deeper as the petals loosen, sucking the juices and thereby causing destruction of the bloom. I thought at one time that the insects showed a preference for varieties of the Ophelia family, for the blooms of these varieties are often badly distorted by their activities. It seems as if they attack any rose indiscriminately, but some varieties are not affected to the same extent. Hot, dry weather favours them, for they give very little trouble in damp spells. Spraying the plants, as for the rose chafer, or with DDT, lindane or malathion should be carried out at intervals, as the thrips, being winged, fly in from other plants when the effects of the spray have worn off.

May bug or large chafer

On light soils the large chafer or May bug can be a terrible pest, the greatest damage being done by the insect in its grub state. It works underground, living on the roots of plants, the rose being one of its especial favourites. The grubs do not congregate together but prefer to work singly over a wide area. In my garden it is pest number one and is particularly fond of newly-planted briar stocks, eating all the roots away and then going on to the next plant, and so on. As a rule the grubs are not difficult to discover and are usually to be found when the plant that has wilted is dug up. Applying aldrin or DDT dust to the soil gives some control, or you can soak the soil round affected plants with liquid DDT, BHC or lindane. The grubs being white and nearly two inches long are easily seen when the soil is being dug, and destruction at this stage is probably the best and surest way of keeping their numbers down.

Rose sawfly

Rose sawflies, although not to be classed as a major pest, can give trouble sometimes. One species feeds on the epidermis of the leaves, leaving them almost transparent. Another is responsible for causing the leaves to roll up. The latter prefers to give its attention to certain varieties and also to those plants growing near trees. Spraying with DDT or BHC at intervals will quickly put a stop to the activities of this pest.

The list of pests I have given by no means exhausts the many different kinds which are liable to attack roses. No good purpose would be served by making the list include those which only occasionally give minor trouble. In any case the treatment for them would be very similar to that already given, and, provided the plants are given as good growing conditions as possible, keeping the plants free from pests should not present very great difficulties.

Diseases

The rose is not subject to many diseases. Those that are the greatest concern to the rose grower are mildew, rust and black spot. Mildew is rather more of a disfiguring disease than a very harmful one. Rust, when it is present in epidemic form as it was in and about 1930, is by far the worst of all. Black spot, only too well known, has, owing to a succession of wet seasons, been rife in many gardens throughout the country.

I do not propose to go into details of the life history of these fungoid diseases, but merely the best way of dealing with them. After all, the great majority of those who grow roses are only interested in keeping their plants free from diseases rather than in acquiring any academic knowledge of them. In any case, much has yet to be learnt about them. For instance, there must be a tremendous mortality of the spores and yet I have never read of it being discovered what is responsible for their death. That very few of the countless numbers that are produced do actually live to carry on the propagation of the kind, there can be no question, as it happens to all forms of life, that the greater the increase the greater the mortality. Whether the knowledge of determining the natural causes of this mortality will be helpful or not, I leave it to those who are more able to give the answer.

Rose mildew

This disease is not nearly as common as it was some years ago. The old Hybrid Perpetuals were very liable to it, and it was a common sight to see beds of these varieties looking as though a flour bag had been shaken over them. Of latter years the number of roses badly subject to the disease has considerably lessened, so much so that those likely to be affected to any great extent could be counted on one hand. By that I mean those varieties that are regularly attacked every year and not those which are only susceptible when the conditions are very favourable. For mildew, like nearly all fungus diseases, is governed almost entirely by weather conditions and humidity. At the same time it would be extremely difficult to give the reason why some plants are badly attacked by the disease, while similar varieties in other situations escape. Sometimes an outbreak will follow a long dry spell and often a wet one, which makes it all very confusing when trying to arrive at a cause.

The disease itself is not difficult to control provided steps are taken soon enough. To wait until the foliage is curled up and powdered white is to make the task very hard indeed, for, although the fungus will be killed on the infected leaves, they will always have the same distorted appearance. The best time to prevent the disease giving trouble is to begin spraying as soon as the first crop of bloom is over. It is unusual to be troubled with it before the end of the first week in July. Moreover, the plants, having had all their spent blooms removed, will be in a better condition for spraying.

Varieties such as Comtesse Vandal, Else Poulsen, Madame Joseph Perraud and George Dickson should be given early attention, for, no matter what kind of weather is experienced, these are almost sure to show early signs of disease.

Powdered sulphur is often recommended as a means of checking the disease. It is not altogether satisfactory and the colloidal copper or sulphur washes are more efficient and not as unsightly as the powder. Karathane, one of the newer fungicides, can also be used.

Rust

This disease, as I have mentioned earlier, has not given a great deal of trouble since 1930. During that time, it was so widespread and severe that very few of the measures taken had any appreciable effect in checking it. Gradually the disease got less and then ceased to give trouble. Nearly all roses were affected, except the Ramblers. It was believed by some authorities that the laxa stock was responsible for the spread of the disease, for R. laxa is very subject to it, but whether that belief was correct or not is open to question. At the present time the laxa stock is very largely used and gives every satisfaction. Whatever the true reason for the outbreak of the disease, it was very bad while it lasted and many rose gardens were almost ruined in consequence. Plants affected were defoliated and the young wood took on a reddish color, followed by weakening of the plants. Some of the more vigorous varieties managed to withstand the disease, but those less vigorous succumbed. The treatment advocated was to spray with a mixture of colloidal sulphur and colloidal copper, and this advice was probably good, and would suffice where the attack is only a mild one.

Black spot

The disease that is giving the greatest amount of trouble with our roses is black spot. Undoubtedly, since the so-called Austrian briar was used for crossing with the Hybrid Teas to give us the brilliant yellow and flame colours, the disease has become much more troublesome. Although these roses are very susceptible to the disease they are by no means entirely responsible, for there are scarcely any roses that are immune, even the common briar. What makes the disease particularly bad in the case of the yellow roses and others of the Austrian briar parentage is that the wood of the plants is soft and sappy and dies back in the winter, especially if the plants have been defoliated in the late summer.

There are many who grow roses and yet have never seen the disease in their gardens. Generally, those who reside in districts where the air is impure would never have reason to worry about taking any precautions to prevent the disease from attacking their plants, as the fungus requires a fairly pure air in which to live. For instance, anyone growing roses in a garden five miles from the centre of London would not be troubled; at ten miles perhaps slightly; at fifteen there would be a liability to serious attack. In the industrial areas of the midlands one can go for miles visiting gardens and nurseries and yet never see a trace of the disease, and yet, in the more rural districts, one will meet with it often.

Since black spot is a fungus disease, its life is governed by weather conditions. In seasons when there are no prolonged wet spells, attacks are slight unless the garden is so situated as to be subject to heavy dew formation that does not dry quickly. The spores, which are airborne, settle on a wet or damp leaf and will make an entry if the leaf remains damp for a few hours; this is why black spot has been such a scourge in the wet summers of the past few years. The spores are reputed to live in the soil or on the plants during the winter. Whether this is so in the latter case I should not like to be too sure, since I know of two personal experiences where the beds had been dug out and the soil replaced with sterilized loam and planted with new plants from a source where the disease is never seen, and yet these plants were completely defoliated by the early autumn. I have known of other instances of heavy infection in beds on new land far removed from other roses.

The fact that the disease is most prevalent in wet weather makes it very difficult to control, for, although it can be done by spraying with colloidal copper or captan, the operation must be repeated as soon as the material has been washed off by the rain. Unlike most diseases which confine their attentions to the unhealthy plants, black spot will more often than not attack plants which appear to be thriving, which has given rise to the belief that lack of potash in the soil makes the plants more susceptible. Whether this is actually so has not been definitely established.

For those whose plants habitually suffer from the effects of black spot, the elimination of those varieties which are most prone should be the first step in dealing with the problem. Roses might be divided into three categories: varieties that are very resistant, those which, while being susceptible, are tolerant, and those which are susceptible and are unable to withstand the effects of defoliation, and get weaker until they die. As a general rule, varieties having a greater amount of foliage are able to tolerate the disease much better than those with less. For example, Mrs. Henry Bowles and Mrs. Sam McGredy are both very susceptible varieties. The former has a fairly long life in the garden, while the latter has a life that is all too brief. A comparison of the amount of foliage of the two varieties will be sufficient to understand my point of view. As it is by the foliage alone that a plant can live and grow, it is reasonable to expect that a rose with a great amount of foliage must have a sounder constitution than one with less, and as far as I have observed this is so. Varieties which I have found weaken considerably and do not recover after being attacked severely by the disease are as follows: The Doctor, Barbara Richards, Phyllis Gold, McGredy's Yellow, Mrs. Sam McGredy, May Wettern, Julien Potin, and Percy Izzard. It will be noticed that among these there are five roses which are constantly being recommended for beginners. This is a pity because, good as they can be in some gardens, they can be an utter failure where black spot gives trouble. Moreover, susceptible varieties, whether they are tolerant or otherwise, are the first to show signs of the disease and soon infect varieties that would otherwise be free from it. Kirsten Poulsen is a sinner in this respect, and is responsible for the spreading of the disease as much as any rose in the garden. Some years ago this rose was almost indispensable, but now it is hopelessly outclassed by the present red Floribundas.

Disease Control By Spraying

Rose mildew and black spot can be kept under control by spraying regularly with captan and karathane. Rust may be checked with colloidal copper or with thiram. Do not be led to believe that these diseases can be kept in check by one spraying or that, after allowing the disease to get a firm hold on the plants, spraying will put a stop to it, for it cannot be done. Spraying, if it is to be successful, must be carried out early and systematically. The first spraying should be given directly after pruning, thoroughly wetting the plants and the surrounding soil and should be repeated when the first leaves have begun to unfold. If the weather remains fairly dry, spraying could be discontinued, but, should there be a wet spell, it should be carried out again on the first suitable occasion. The evening is the best time of the day for this operation. It should never be done in bright sunshine or burning of the foliage may result.

The mulching of the beds with peat or grass mowings is recommended for keeping black spot in check, the idea being that the spores in the soil are prevented from rising. The fact that growing roses in new, spore-free soil does not prevent an attack, seems to discredit this theory. That the practice does have the effect of keeping the disease down is not open to question, but, I fear one must seek other explanations for the reason. One great objection to the use of grass mowings is that if annual meadow grass is one of the constituents of the lawn, a great deal of trouble is given by seeds of this grass growing in the beds. Peat, on the other hand, has the effect of keeping weeds down and at the same time gives a pleasant appearance to the beds.

Sprayers

There are a great number of sprayers on the market, from the small canister type to those used in orchards and nurseries and operated by mechanical means. The efficiency of sprayers is governed by their ability to wet the whole of the tree or plant and for that a certain amount of force is necessary. For use in average-sized gardens, I have found the syringe type with a double action and a length of hose, which is fed from a bucket containing the spraying mixture, easy to use. Other sprayers suitable for use in small gardens are those that have a pressure pump attached. All that is required is to put in the liquid and pump the pressure up to about 80 1b. per sq. in. For the young and active this pumping business will have no terrors, and once it is done, the machine will go on spraying until the sprayer is empty. Not being in the first bloom of youth I find pumping rather tiresome, so much so that I have devised a sprayer on similar lines which can be pumped up by the use of a car foot-pump, and that is the sprayer I now use. One word of caution: in the use of the syringe type, care should be taken to clean it thoroughly with clear water, especially if tar oil wash is used for fruit-tree spraying, since this substance will tend to make it sticky and hard to work when used later.

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