All plants have pests. Roses have their share of enemies but you can control them, and get five or six months of bloom, with no more time than that required to keep irises or chrysanthemums healthy for five or six weeks of bloom. Also, roses are pretty tough. They may look rather ratty if you neglect them for weeks on end but they will usually survive to another year when you can treat them better.
For new roses, pest control starts before planting, when you open that package from the nursery. As you remove each bush, look it over very carefully for crown gall, a bacterial disease. This may appear as a fairly large, roundish swelling, with an irregularly roughened surface, near the bud union or as small galls on the roots. Watch also for small swellings in the roots clue to root-/mot nematodes. Diseased roses are the exception rather than the rule but they occasionally slip through inspection. Any reputable nursery will replace such bushes so do not take the chance of getting bacteria or nematodes into your soil.
For established roses, pest control starts at spring pruning. If you prune before winter protection is removed you may have to repeat some of it after all the extra soil has been taken away. Cankers, discolored areas, and rose scales, round, dirty white shells, are usually near the base of canes, which may have to be cut at ground level. Prune healthy canes moderately but make each cut just above a bud. If you leave even half an inch of stub, the cane dies back to the bud and this dead tissue affords entrance to some of the weaker canker fungi.
Many people spend a lot of time painting pruning cuts to prevent entrance by carpenter bees and other borers. I have never painted a pruning cut myself but I sometimes have to doctor roses that have been treated with injurious materials. If you must paint, orange shellac is probably the safest and least conspicuous material. I do, however, often apply a dormant spray right after pruning, one part liquid lime"sulfur to nine parts of water, for this kills most of the scales, some of the canker spores spread around during pruning, and may slightly reduce blackspot, although recent research indicates a dormant spray has little effect. This spray must be applied before the buds have broken into identifiable young leaves; otherwise there will be burning.
A mulch is another way to prevent disease. Apply it after the first feeding and as soon as the ground has warmed up slightly. A good mulch makes a mechanical barrier between infective material on the ground and developing leaves overhead. More important than that, it prevents splashing. The spores of the blackspot fungus can be spread only by water; they are not blown by wind. When rain, or the hose, hits hard-packed earth it can splash a long way; when it hits a proper mulch it sinks in gently with little splashing.
Regular Treatment
Soon after your roses come into full leaf, start using an all-purpose spray or dust and keep it up every single week until hard frost. This may take only a few minutes a week, but the treatment must be regular if you wish fine flowers, unblemished foliage. In most of Mid-America the most important ingredient in a combination pesticide is a fungicide for blackspot. The well-known symptoms of this disease are actual black spots with faintly fringed margins scattered over leaves, and small indefinite dark lesions on canes. VVith some varieties, the leaves quickly turn yellow and drop; with others, there is extensive spotting but relatively little defolia" tion.
Copper, sulfur, ferbam, captan, maneb, zineb, and recently glyodin and phaltan have all given satisfactory control of blackspot under certain conditions. Copper may be injurious in cool, cloudy weather, sulfur in very hot weather. Black ferbam is generally safe but sometimes disiiguring. Widely used captan seems to be more effective in some formulations and areas than in others. Maneb controls blackspot and also Cercorpora leaf spot which is sometimes a problem in Texas, Arkansas, and other Southern states. Zineb is good for blackspot and also rust, which produces orange-red summer pustules and black winter pustules on underside of rose foliage in a few states. Glyodin is promising but, like sulfur, has to be used with caution at high temperatures. Phaltan may be marketed this year; it is still being tested.
The new organic fungicides, with the possible exception of phaltan, do not control powdery mildew, that white coating over buds and tender foliage which distorts blooms and sometimes blisters and curls leaves. Sulfur and copper control mildew fairly well but karathane (sold as Mildex) is specifically for this disease. It is included in some combinations but can be applied separately, at the rate of two-thirds teaspoon to a gallon of water. Actidione and one or two other antibiotics are effective against mildew but are sometimes injurious, causing a yellow Hecking of foliage.
Fighting Aphids
Organic insect pests usually begin with aphids, pink and green plant lice which cover new shoots and deform buds and blooms. Almost any pest spray and contact insecticide will take care of aphids, with the washing action of a spray more helpful than a dust. Still effective but presently out-of-fashion is nicotine-sulfate used with soap. Pyrethrum and rotenone, malathion, and lindane are now in favor. Small bombs, pressurized sprays, can be used to spot"treat infested buds on one or two bushes but are inadequate for general spraying. Despite their recent popularity with home gardeners, I am not yet ready to concede that hoseattachments give as good control of black spot as regular tank sprayers. I do admit that they can be quite useful for aphids, if properly adjusted so there is no danger of too strong a dosage. Malathion readily burns rose foliage unless used at low strength.
Leafhoppers appear soon after aphids. They are small, light-colored wedge-shaped insects, sucking always from the undersides of leaves, causing a white stippled pattern on the upper surface. They disappear in midsummer, come back in greater hordes in autumn. DDT gives excellent control; rnalathion is fairly good. The rose-slug, larva of a sawfly, is another early spring pest. It is very small, velvety green, shaped like a tadpole, and it makes windows in leaves by eating everything except epidermis and veins. It is readily controlled by rotenone, lead arsenate, DDT, or other pesticides, if applied early enough. To my mind, spider mites are the worst of the animal pests on roses.
