Rose Pests on the Run: Essential Tips to Protect Your Garden

Roses are heir to various diseases and pests, but rarely more than one at a time. This is a great blessing.

Furthermore, the means of combating them are easy and take little time. If you can spare 15 minutes a week (in the average rose garden of 50 plants) for prevention and cure, you are set.

It is essential, though, to use the right material at the right time and to continue to do so at weekly intervals—at least.

The infected or buggy garden indicates a lazy gardener or a gardener who has planned way beyond his time allowance. But unfortunately, those of its who are maintaining gardens of upwards of 500 roses without help accept a certain amount of disease and pest damage as a necessary evil.

You have no excuse if you have less than 100 plants, for they require so little time. Almost every problem can be controlled and conquered with the materials we describe.

All these troubles can happen to growing roses. However, most will not; little permanent harm will be done if they do.

Controlling Rose Pests And Diseases

What is more important, rose pests and diseases can be controlled. Let it be said here that, in Richard Thomson’s experience, spraying is far more effective than (lusting. (Helen Wilson is lazier and prefers dusting: also, she has fewer roses.)

Sprayers vary from the $1.50 no-good type, which holds only a pint, to mammoth power machines for orchards. What you buy depends on your pocketbook, but any sprayer holding less than a quart is generally a good use of money.

Pressure cannot be held in a small tank, and variations in Italy clog the spray orifice with sediment. Get a sprayer bigger than you need, and if some solution is left over after the job, throw it out—thankfully.

The waste cost is tiny. And when you mix materials, really mix them, and follow the instructions, even if it takes a few minutes longer.

One word of caution: If you use a weed killer for the lawn, DO NOT use the same sprayer for roses and weeds.

No matter how carefully you clean and rinse the tank, the weed killer will persist, and only a trace is necessary to finish your roses.

(Such injury causes twisted, stunted growth, which may correct itself if not too serious and if left alone, but it also may not!) Use two different sprayers, and mark the one for weed killer with red paint!

All Purpose Preparations

An enormous number of preparations have been manufactured to keep your roses healthy.

For aphids alone, you have ten from which to choose. Then, there is a separate spray or dust to control or cure each thing.

If you are a beginner, not too apt at diagnosis, or have only a dozen bushes, you will do well to get the “all-purpose” preparations.

These are convenience itself, and, like other conveniences in life, they cost a little more than if you use a specific material for a specific ailment or, having collected the specifics, make up your spray.

Also, the all-purpose dust or sprays are bound to be wasteful for, when the only ailment is, say, aphids, you will also be applying controls for beetles and black spots.

If you buy a do-everything “proprietary” preparation, be sure it contains (read that label!) these materials or their equivalents (the man who sells it should know):

Captan
Malathion
Methoxychlor or DDT

We mention these specifics because it is our experience that they do the best job. Various other materials are also good, but we recommend them from personal experience, which could be more encompassing.

If other things have given you good control, by all means, stick with them.

Aphids

Also known as plant lice or green flies, aphids are soft, little, green, or brownish-sucking insects congregating at the tips of growing shoots.

They insert pointed beaks under the bark and draw out the juices. We have seen them in layers three deep.

Since they will not penetrate hardwood, they are only found in weak growth. Unchecked, they cause misshapen blooms and little shoots.

Control: Use nicotine sulfate, Oh teaspoons per gallon, plus a shake of soap flakes. Be careful of the concentrate; it is poisonous. DDT will also kill aphids.

A strong stream of water from the hose will wash off most of them, but they will return. They are persistent, especially in the spring.

Beetles

Rather than enchant you with descriptions of the myriads of these beasts, we lump them under this one heading. The same treatment gets them all—no need to know an echo from a rhabdovirus.

In the East, there is only one serious beetle, the Japanese. Those of you who have yet to make his acquaintance can have no idea what trouble is.

We have seen whole gardens denuded of all bloom and all foliage in three days. However, the Eastern infestation has decreased in recent years, and the spread of this most horrible of all beetles has been slowed to a near stop.

Control: Apply DDT or methoxychlor. This will ensure the demise of beetles of all kinds. Lead arsenate is also used, but if children are around, this is not recommended.

Keep growing shoots covered with spray during infestations, even if this disfigures plants, and do not worry. You will kill thousands of beetles, and the plants will survive the treatment.

A word on beetle traps. These contraptions kill beetles, to be sure, but they seem to attract more than they destroy.

Also, if you want to pick beetles by hand, go ahead. You will get lots of exercise, but it will only reduce the beetle population a little.

You can kill the beetle grubs by treating the soil with chlordane-5 pounds of 5% percent dust per 1000’ square feet, lawn and all. This will help, but you’re wasting your time if the neighbors do not do it too.

Controlling Black Spot

Black Spot

This is undoubtedly the most serious rose disease in the United States, though not serious in California and the desert states. Black spot depends on summer rainfall for its existence and spread.

This fungus is bewildering to the novice and a cause of real concern to the initiated. The symptom is the appearance of fringed black spots on the leaves. The spots enlarge and may coalesce.

Ultimately, leaves turn yellow and fall off. Black spot is infectious, and all your roses may be defoliated in a few weeks if you do not take prompt action.

Spores are spread by splashing water, either by rain or overhead watering. Each spore will germinate and penetrate a leaf if this is wet for six continuous hours.

Since either an evening rain—or heavy rainfall—or later afternoon watering will accomplish this, it is obvious that conditions are frequently suitable in summer. However, this fungus penetrates and grows inside the leaf, so control is difficult under the cuticle.

The first spring infection may come from spores wintered over on old leaves on the ground or—much more frequently—from lesions on the canes.

To be sure, a thorough clean-up of last year’s leaves from the beds is important, but it is not the cure-all. Too often, black spot infections start well up in a plant, even high in a climber.

This condition could not have come from spores splashed from old leaves on the ground. More probably, cane lesions (spots of infection) are the cause.

These are often very small and difficult to detect. Since low pruning is not usually good practice, some infection centers are bound to be on wood remaining from the prior season.

Control: Protect the foliage with a film of captan spray at any time it is likely to be wet for six hours. “Sticker” materials (sold as such) added to the spray will hold a film on leaves through several days of steady rain, so protection is possible.

Captain, used according to the manufacturer’s directions—and used faithfully—gradually eradicate black spot.

Start early in the spring with a double dose before leaves have unfolded. Continue at least once a week, repeating with normal-strength applications.

In 10 years, we suspect the black spot will no longer be serious because of the captain.

Borers

Several kinds of larvae cause damage by burrowing under the bark of rose canes. The type of damage varies according to the pest. This is what to look for:

Rose Sawfly

The larvae of this insect bore directly down into the pith of the cane, starting at some surface cut.

Rose sawfly is common in the East but can be checked by painting pruning cuts with asphalt tree paint. (Damage is rarely severe.)

Rose Stem Saw Fly

This one hatches in the puncture of an egg-laying wasp. Larvae bore into and through the canes, causing dieback.

Giwler

The larvae make long spiral tunnels under the bark. These are visible as raised welts. Often a cane will crack and break off at the infected spot. (Especially bad on R. rugosa and R. hugonis.)

Control: Since the larvae or borers operate inside the plant, the only sure remedy is to cut off the canes below the areas of damage.

Cankers

Spots of dead wood appear. These enlarge and may encircle a cane, destroying life above the circle. Brown Canker: This starts with tiny purple spots on the canes.

Spots enlarge to show a white center. When growth begins, the spots grow to several inches and turn brown with purplish edges.

Control: Spray dormant plants in early spring with a strong or “dormant” lime-sulfur solution. If you discover cankers in the early, minute, or at the larger brown-colored-lesion stage, cut off the canes below the areas of damage.

Stem Canker (Common Canker)

We have yet to find a rose garden where this ailment is somewhat absent. Dark gray to black patches surrounds breaks or wounds in the bark.

Sometimes canes are girdled and die above the lesion. Stem canker is related to wounds in the bark.

Control: Lie carefully with your hot, and you will not have to worry about this. It can be serious where cultivation is careless.

Caterpillars

All of them live by eating foliage, rose foliage included. We assume that every gardener knows a caterpillar when he sees one.

Control: Apply DDT or Methoxychlor.

44659 by Richard Thompson

In their introduction to this article, the authors stated:

“Roses are heir to various and sundry diseases and pests, but rarely more than one at a time. This is a great blessing. Furthermore, the means of combating them are easy and do not take much time. If you can spare 15 minutes a week (in the average rose garden of 50 plants) for prevention and cure, you are set. It is essential, though, to use the right material at the right time and to continue to do so at weekly intervals —at least.”

Varieties Of Rose Pests

Continuing the discussion of rose pests, the following are listed alphabetically.

Dieback

This is often referred to by great wide authority as a disease. However, it seems to us that this is as ridiculous as suggesting that headache is a major human disease.

Headache is a symptom of something else, and so is tieback. Likewise, cankers and borers will cause tieback.

Also, when blooms are cut or snapped off just below the calyx, stems will die back to the first leaf, for no leaf above supports growth. This is another type of dieback.

Control: Look for the real cause of moderate growers. Climbers and strong plants seem to resist it quite well.

Control: It is probably best to dig up and burn infected plants. Since the organism which causes the galls is a bacterium, it also digs out and discards the soil in which the plant

grew.

Midge

This common greenhouse pest has recently become more serious outdoors.

Tiny orange-white larvae feed in the buds and on stems directly below. As a result, older buds may bend to one side.

Control: Apply DDT. Midge is rarely serious but can be annoying.

Nematodes

Nematodes are serious in the South. Longish cylindrical galls on roots characterize nematodes.

Swellings come from within the roots and are not externally (as is supposed with crown gall).

Control: There is no cure; an infected plant will die. Examine your roses for nematodes before planting. If any dug-up rose shows the disease, burn it, and get rid of the old soil.

Powdery Mildew

Anyone who has grown roses is familiar with this one, probably the most widespread of all difficulties, and although not as serious as black spot, a cause of plenty of grief.

In case you do not know, mildew is a felty white mass resembling powder, surrounding new shoots and making patches on foliage.

It has never, in our experience, succeeded in killing an outdoor plant, but it can stunt and deform growth. Mildew is a disease of high humidity.

Unlike black spots, it does not require immersion in water to germinate the fungus spores.

Actually, germination is inhibited by free water on the leaf surface; near saturation is required. Therefore, a warm moist day followed by a cool night is ideal for mildew germination.

Spores are broadcast by wind or by any physical disturbance of the leaf. Spores probably float a considerable distance on a good breeze.

Control: Apply Karathane. This will give complete control if used as directed.

Karathane will not eradicate mildew because the fungus can renew itself from dormant spores that no chemical known to date can touch, but it will kill and control the active fungus on the leaves.

However, do not apply when the temperature is over 85° degrees Fahrenheit; that heat in our gardens has caused some foliage burn.

Red Spider

These are becoming a serious problem indeed. Not spiders at all, but tiny mites. They congregate under rose leaves and suck the juices.

Multiplying and operating best in hot, dry weather, they cause yellowing and browning of leaves that are often mistaken for drought damage.

Examining the underside of affected foliage will often show a faint mass of white cobwebs.

A low-power glass will reveal mites working busily. Plants may be completely defoliated in midsummer.

It is a law of nature that if predators of a pest are reduced, the pest runs riot. Before the use of DDT, red spiders were kept in better control by the insect enemies, which DDT now destroys.

Although essential, DDT has allowed the spider mite to range unchecked. Since DDT does not affect the mite, we must go to other sources for control.

Control: We have three control materials—aramite, dimite, and malathion. Use carefully as directed, for these are somewhat poisonous to humans.

Rodents Mice

The dark-brown pine mouse, a fairly serious enemy in the eastern United States, burrows in rose beds and eats roots.

Plants that have been attacked (usually during the winter) collapse and (lie at the start of the growing season.

A sharp tug at the crown of an affected bush will bring up nothing but a gnawed stump.

Control: Place poison baits (usually strychnine-impregnated grain in small plastic covers) in the burrows.

This is a somewhat effective control. However, the best solution is probably a hungry cat.

Moles and Rabbits

MOLES: The damage they do is more aesthetic than serious.

These are insect eaters; while mole tunnels disturb roots in a rose bed, plants are not physically harmed.

There are dozens of so-called mole remedies, but none are particularly effective.

RABBITS: You may love them, but we do not. When the ground is snow-covered, they gnaw and girdle canes and do considerable damage.

Control: Chase them!

Rust Fungus

Rarely seen in the East, this fungus is serious in California and nearby areas. In spring, tiny orange-to-yellow spots appear under the leaves.

Later the spots enlarge and become powdery orange masses. Finally, the orange spores are replaced by black ones, which carry the fungus through the cool weather.

Rust can defoliate a plant almost as effectively as blackspot, and it is a serious disease in some areas.

Conditions for germination are similar to those for blackspot—splashing water and four hours of being wet.

Control: Use captan as suggested for blackspot.

Thrips

These tiny suckers and chewers are serious about roses with soft petal age and light-colored blooms.

Infested buds ball. Examination reveals rasped and roughened petal edges deep within the bud.

If the bud is opened, many tiny, thin, yellow-to-light-brown insects are discovered. Exposed, they scurry to concealment.

Control: Spray with DDT, which is somewhat effective, but since thrips work between the petals and inside buds, complete control is a problem.

To prevent the many ills, a reasonably exact schedule must be set up and maintained.

While winter is still with us, a “dormant” lime sulfur spray must be used, wetting plants and beds thoroughly.

The regular spraying or dusting program must begin as soon as the leaves unfold and be maintained until frost has defoliated the plants.

Spray Schedules

How often? This has a variable answer.

Black spots and rose rust become more annoying in wet seasons because of their peculiar infection methods.

In dry seasons, spider mites will be more of a problem. Therefore, spray schedules must be altered to suit the prevailing weather conditions.

Normally, with the recently available materials, roses should be sprayed or dusted at least every week and every few days in cases of serious infection or infestation.

If only a few plants are involved, this will consume but little time. However, attention to rose plants must be regular if you want the best results.