Rose Pests – Pests Affecting Rose Plants
Pests Affecting Rose Plants
The most common and most prolific of pests. Most gardeners are familiar with these tiny insects, which are found on under the flower buds, particularly on young soft growth. They are also called greenfly, although there are many species which may be amber, reddish, black, or grey as well as green. Natural predators such as ladybirds, sparrows, and tits — or a sharp squirt of water from a hose—will certainly dispose of some aphids but will not as a general rule control them completely.
Aphids reproduce rapidly, so it is wise to spray them with an insecticide twice within three days to ensure eradication. Early in the season a fine, mist-like spray of malathion is effective; in warm summer temperatures of 18°C (65°F) or more I find that nicotine is still one of the most effective cures. Alternatively derris, which is harmless to most animals, may be used. (But note that it is deadly to, so avoid using it if your garden contains an ornamental pond or running water.) A more recent preparation, formothion, is an effective systemic insecticide — that is, a poison that a plant is able to absorb without any harm to itself and that will attack a sap-sucking insect such as an aphid. Formothion can be watered into the around the plant and will be taken up by the plant’s roots.
The presence of these insects is indicated by the tattered and often contorted appearance of shoot tips. The adult insect, about 6 mm in) in length, is metallic green in colour. It moves rapidly if disturbed, and is best dealt with by use of a systemic insecticide such as fenitrothion. Spray both plants and soil.
Caterpillars of various butterflies and moths feed on rose leaves and also attack buds on occasion. Generally shot-holed leaves are the most familiar sign, but leaf edges also suffer some damage. If only a few plants are affected, you can usually pick off the caterpillars by hand — but make sure to look on both sides of every leaf. If damage is more widespread, use a systemic insecticide such as fenitrothion.
FROGHOPPER OR CUCKOO-SPIT INSECT
An insect easily identified by the frothy sap or spittle-like mass which gives the small yellow nymph protection. If only a few are present, you can kill them by squeezing them between your finger and thumb. Larger numbers will require the use of an insecticide sprayed with enough force to penetrate the protective spittle. Malathion is effective as an insecticide; a systemic insecticide will also aid control.
The leaf-rolling sawfly has become something of a menace in recent years, particularly in rose gardens that have sheltered corners or are overhung by trees — areas in which the fly likes to hover. The pest, the adult of which looks rather like a flying ant, causes rose leaves to roll or curl up. Once this has happened, it is too late to spray, and picking off by hand and burning becomes the only remedy. Preventive spraying in May and June, using either malathion or trichlorophon, should help to lessen the damage.
THRIPS OR THUNDER FLIES
These tiny, black-winged insects damage petal margins in very hot weather, and sometimes cause discoloration and distortion of young growth and buds.
Damage is generally confined to roses with light-coloured, particularly the ‘Ophelia’ group. Spray early in the season, applying derris, malathion, or nicotine, concentrating especially on the tips of young growths and buds.
Red-spider mites can be a serious pest in very hot, dry seasons on roses in warm, sheltered situations. The almost microscopic mites are difficult to detect; moreover, they live on the under- side of the leaves, which soon become an unhealthy blanched bronze in colour and later fall prematurely. A fine silky web is a sure pointer to the presence of this pest, which quickly builds up a resistance to some pesticides (as I have found with malathion). Systemic insecticides or liquid derris can be tried. Preventive measures include the clearing away of any weeds or rubbish around the plants.
Leaf-cutting bees are similar in appearance to ordinary hive bees. The female cuts semi-circular portions neatly out of rose leaves, which she uses in the brood cells of her nest. The damage done, however, is not extensive enough to warrant destruction of the nests.
ROSE SLUG SAWFLY
The rose slug sawfly lays its eggs in May on the edges of young leaves. The resulting larvae, almost transparent, devour the internal tissues of the leaves until only a silvery skeleton is left. Spray both sides of the leaves with malathion or trichlorophon in May and June; a second spraying in July or August may also be necessary.