Keeping roses healthy

My friend seems to spend half of his gardening life dealing with rose pests and diseases. I want to grow roses too, but is it possible to buy varieties that are likely to be trouble-free?

It is certainly true that some varieties are inherently healthier than others. However, it is not possible to be very precise about the healthiest roses, for their resistance to disease can depend on the conditions under which they are grown, the type of soil, how well they are looked after, and even the part of the country in which the grower lives.

Unfortunately, regarding the last factor, there is not a set pattern of ‘healthy’ and ‘unhealthy’ localities. A wise gardener looks around other local gardens, parks, and nursery display beds to see how the roses are doing before he buys any for his own garden. One or two varieties often stand out with shining, healthy foliage in the midst of a sea of mildew on those surrounding them. It can be taken for granted, however, that a rose that is well looked after and that grows strongly will be less likely to suffer badly from disease.

Despite what has been said above, there are certain roses that have been shown to be reasonably disease-free in most parts of the country. Among the best of these are the LARGE-FLOWERED ‘Adolph Horstmann’, ‘Alec’s Red’, ‘Alexander’, ‘Alpine Sunset’, ‘Blessings’, ‘Double Delight’, ‘Ernest H. Morse’, ‘Grandpa Dickson’, ‘Just Joey’, ‘My Choice’, ‘Peace’, ‘Piccadilly’, ‘Pink Favourite’ (outstanding), ‘Silver Jubilee’, ‘Sunblesf, ‘Troika’, and ‘Wendy Cussons’. Of the CLUSTER-FLOWERED varieties, the healthiest ones include ‘Allgold’, ‘Anne Harkness’, Arthur Bell’, ‘City of Belfast’. ‘Dame of Sark’, ‘Fragrant Delight’, ‘Korresia’, ‘Living Fire’, ‘Margaret Merril’, ‘Mantangi’, ‘Mountbatten’, ‘Queen Elizabeth’, ‘Rob Roy’, ‘Southampton’, ‘Trumpeter’.

Healthy CLIMBERS include ‘Mermaid’, ‘Compassion’, and ‘Aloha’. And among the rugosa family of shrub roses disease is virtually unknown.

How do I go about spraying roses?

Except where a few exceptions are cited in the five answers that follow this, spray only when the first signs of a disease or pest are seen. Sprays with the longest-lasting effect (several weeks) are the systemics, which enter the plant tissue and so cannot be washed off by rain.

Evening is the best time to spray; never spray in hot sunshine, or scorched leaves may be the result.

How can I recognise and deal with blackspot?

This fungus shows as round, black spots with fringed edges on the leaves, at first usually on the lower, older ones, towards the end of June or in early July. If neglected, the spots rapidly enlarge, the rest of the leaf yellows, and it will drop to the ground. Such defoliation weakens the plant, and the fungus spores will spread rapidly to neighbouring bushes. Spray with fungicide based onbenomyl, triforine, triophanate-methyl, bu-pirimate-triforine (almost certainly the best), or fenarimol.. In bad blackspot areas -your neighbours will soon tell you if you are in one – preventive spraying maybe needed every 10 days or so from the second half of June onwards. Always remove affected leaves that drop on the beds. Spray the dormant bushes and surrounding earth with Bordeaux mixture two or three times in winter to kill over-wintering spores.

How do I recognise and deal with mildew?

This is a greyish, powdery-looking covering, usually first seen on young leaves and the flower stalks. It will spread rapidly over the whole bush and to others. It is not fatal, but if bad it will distort the foliage and flowers and it is very unsightly. Spray at first signs with the fungicides listed for blackspot (above) and give the same winter treatment to the beds.

How do I recognise and deal with rose rust?

This is much less common than mildew and blackspot, and many varieties seem immune to it. First signs are small orange pustules under the leaves, and these gradually turn black. Rust can be a killer if neglected, but the only really effective remedy, an oxycarbon spray, is not at present available in the small quantities needed by the average gardener. However, zineb, mancozeb, thiram, or maneb are worth trying.

How do I recognise and deal with sap-sucking pests?

These include aphids or greenfly, which are tiny green (sometimes brown) insects that cluster on young shoots, leaves (often on the undersides), and flower stems, and increase with incredible rapidity. There may also be froghoppers, which are large greenish-yedllow insects which hide in easily-seen blobs of foam. Spray both with derris (norsystemic), manazon, fenitrothion, dimethoate, or formothion.

How do I recognise and deal with leaf- and petal-eating pests?

These include chafers (green flying beetles which nibble petals and anthers), thrips or thunder-flies (tiny brownish insects, more common in hot weather, which nibble flower buds), and the trotrix moth and other caterpillars. Some of the last hide in rolled-up leaves, and the lacky moth caterpillar makes a silken ‘tent’. With a mild infestation, caterpillars can be removed by hand. Otherwise spray both these and chafers with trichlorphon or fenitrothion; the latter will deal with thrips as well. The leaf-rolling sawfly lays eggs in the leaf margins, and the leaf rolls into a tapered cylinder that protects the grub. To deal effectively with this pest, you must act before the leaf rolls. Spray it in late April and again in early May with trichlorphon or fenitrothion if infestation has been bad in previous years; otherwise, simply pick off the affected leaves and burn them.

11. April 2017 by admin
Categories: Featured Articles | Tags: , , , , , , | Comments Off on Keeping roses healthy

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