Curly leaf on roses

Tiny mite spreads ugly disease by feeding on roses

Roses are typically viewed as one of the most beautiful flowers, but in rare cases a tiny pest can cause gnarly looking, new growth on rose bushes.

Rose leaf-curl mites feed on roses and cause rose rosette virus, also known as RRV. The extremely small eriophyid mite feeds on plant sap from the tender stems and leaf petioles. The pest alone causes little damage while feeding, but if it is a carrier of RRV, symptoms begin to appear in the rose typically within one to three months.

There is no cure for RRV and it is not always preventable, since there are no vaccines for plant viruses.

Causes thick, succulent stems

Infected roses exhibit reddened terminal growth on infected branches, and the stems become thicker and more succulent than those on unaffected parts of the plant. These stems exhibit an abnormally high number of pliable thorns, which may be either green or red.

Infected rose bushes produce less flowers and the petals may be distorted and fewer in number. Rose leaves that develop on infected branches are smaller than normal and may be deformed similarly to herbicide injury by 2,4-D.

Lateral branches may grow excessively from main stems and create a witch’s broom symptom, much like injury from herbicide glyphosate (Roundup and other brands).

Treat nearby rose bushes

To reduce the spread of leaf-curl mites from the site of an infected rose, nearby roses can be treated with an insecticide spray containing bifenthrin or a horticultural summer oil every two weeks between April and September. This may help prevent additional plants from becoming virus infected by any sap-vectoring mites.

Symptoms of the virus generally become evident in the late spring to early summer and progress during the growing season. By late summer or fall, the plant will have a noticeable amount of abnormal, gnarly growth.

Once the rose becomes infected, RRV moves throughout the plant and the entire bush becomes infected. By the time symptoms are evident in a rose, the virus may have spread to adjacent roses by the movement of the mites.

Only affects roses

Infected plants typically die within a couple of years. The good news is RRV only affects roses, so other plants in your garden won’t get this disease unless they are closely related to the rose plant.

Since there are no treatments for plant viruses, infected roses should be immediately removed, then burned or bagged for disposal. Also remove any roots that might re-sprout later. Do not leave an uprooted, infected plant in the garden, as the mites may leave this bush for other nearby roses.

When planting new roses, space plants far enough apart so that they do not touch in order to minimize potential spread of these types of diseases.

Because RRV is systemic within the infected rose plants, grafting infected stems onto other rose plants will transmit the virus. Nursery growers may infect roses this way through poor propagation practices.

Pruning shears and other tools used on diseased roses should be disinfected with rubbing alcohol or a 10 percent diluted bleach solution before being used on healthy plants. Sap left on the pruners can contaminate other roses.

For more information on growing roses, refer to the University of Georgia Cooperative Extension publications at www.caes.uga.edu/publications/.

Rose problems

Fungal problems

Black spot

Black spot, one of the most common diseases of roses, is caused by the fungus Diplocarpon rosae.

Early black spot on rose leaves.

Infection results in irregular black spots with fringed margins developing on leaves and young stems. Affected leaves turn yellow and drop prematurely and if defoliation is severe stem dieback can occur. Spores are spread by wind and water-splash.

To control black spot remove and destroy all diseased material. When new growth occurs spray bushes with mancozeb, myclobutanil or triforine. Organic controls include sprays containing bicarbonate of soda (potassium bicarbonate).

Powdery mildew

The fungus Sphaerotheca pannosa causes the disease powdery mildew on roses. New growth is most susceptible. Leaves, stems, and flower buds develop a pale grey powdery coating, leaf edges may scorch and curl inwards, and buds may be deformed. The fungus can overwinter in infected buds. The disease spreads by wind-borne spores.

Powdery mildew.

To control powdery mildew, remove and destroy diseased material. During the growing season spray bushes with mancozeb, lime sulphur, tebuconazole, myclobutanil or triforine. Organic sprays contain bicarbonate of soda (potassium bicarbonate). Make your own spray by mixing one part full cream milk with ten parts water and spray at the first sign of the disease.

Botrytis

The fungus Botrytis cinerea affects most above ground plant parts. Flowers often become spotted or may fail to open, eventually becoming covered in a grey or brown mould. Purple lesions occurring on canes are often caused by botrytis. Spores are wind-borne and also can be spread on garden tools like secateurs.

To treat botrytis remove and destroy diseased material. Spray bushes in late summer and autumn with mancozeb. When pruning, disinfect secateurs in bleach before progressing to the next bush, and apply fungicide immediately to protect wounds from infection.

Downy mildew

The fungus Peronospora sparsa causes downy mildew. Purplish-red or dark brown, irregular, and often angular, blotches develop on leaf surfaces, and during humid weather a blue-grey, downy growth of fungus may appear on the undersides.

The leaves droop, turn yellow, and may drop. Stems and calyces develop purple or blackish spots, streaks, or blotches. Petals have brown, dead areas. Infected buds may produce deformed flowers. Spores are wind-borne but need free water on the leaf surface to germinate.

To control downy mildew remove and destroy diseased material and spray bushes with a copper fungicide.

Get out your notebooks – it’s time for a lesson in flower anatomy! Most of us know about petals and stems, but for you with curious minds, here’s a more thorough rundown of what makes a flower a flower.

Petal

Petals are what give a flower its unique shape, and are often brightly colored to attract insects and critters, which unwittingly aid in the fertilization of ovules through pollination.

Sepal

These are the small, leaf-like parts growing at the base of the petals. They serve to protect the flower before it blossoms.

Peduncle

This refers to the stem or stalk of a flower.

Receptacle

This is the thickened part at the bottom of the flower which holds its major organs.

Pistil

This is the female organ of the flower. It consists of four major parts:

  1. Stigma – The head of the pistil. The stigma receives pollen, which will begin the process of fertilization.
  2. Style – This is the name for the stalk of the pistil. When pollen reaches the stigma, it begins to grow a tube through the style called a pollen tube, which will eventually reach the ovary. The style therefore acts as a buffer against pollen contamination, since only compatible pollen is able to grow a pollen tube.
  3. Ovary – The base of the pistil. This organ holds the ovules awaiting fertilization.
  4. Ovules – These are the flower’s eggs, located inside the ovary. Upon fertilization by pollen, they will eventually grow into a seed. In fruit plants, pollen will not only spark the growth of a seed, but a surrounding fruit as well.

Stamen

This is the male organ of the flower, consisting of two major parts:

  1. Anther – The head of the stamen. The anther is responsible for the production of pollen, which will hopefully be transported to the pistil by animals or insects, such as bees. This is a crucial part of the reproduction of the plant.
  2. Filament – This is the stalk that holds the anther and attaches it to the flower.

Making More Flowers

It’s amazing for nature to provide a flower with the ability to reproduce without the need for a mate, but not all of them do!

Some flowers have only male or female organs, and require a separate flower of the opposite gender to reproduce. We call these Imperfect Flowers. Perfect Flowers, on the other hand, have both a stamen and a pistil, and are able to reproduce on their own.

Parts of a Flower

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Flower

Form and types

Basically, each flower consists of a floral axis upon which are borne the essential organs of reproduction (stamens and pistils) and usually accessory organs (sepals and petals); the latter may serve to both attract pollinating insects and protect the essential organs. The floral axis is a greatly modified stem; unlike vegetative stems, which bear leaves, it is usually contracted, so that the parts of the flower are crowded together on the stem tip, the receptacle. The flower parts are usually arrayed in whorls (or cycles) but may also be disposed spirally, especially if the axis is elongate. There are commonly four distinct whorls of flower parts: (1) an outer calyx consisting of sepals; within it lies (2) the corolla, consisting of petals; (3) the androecium, or group of stamens; and in the centre is (4) the gynoecium, consisting of the pistils.

  • flower partsParts of a flower.Encyclopædia Britannica, Inc.
  • (Left) Generalized flower with parts; (right) diagram showing arrangement of floral parts in cross section at the flower’s baseEncyclopædia Britannica, Inc.

The sepals and petals together make up the perianth, or floral envelope. The sepals are usually greenish and often resemble reduced leaves, while the petals are usually colourful and showy. Sepals and petals that are indistinguishable, as in lilies and tulips, are sometimes referred to as tepals. The androecium, or male parts of the flower, comprise the stamens, each of which consists of a supporting filament and an anther, in which pollen is produced. The gynoecium, or female parts of the flower, comprises one or more pistils, each of which consists of an ovary, with an upright extension, the style, on the top of which rests the stigma, the pollen-receptive surface. The ovary encloses the ovules, or potential seeds. A pistil may be simple, made up of a single carpel, or ovule-bearing modified leaf; or compound, formed from several carpels joined together.

pistilLily with a pistil surrounded by stamens.iStockphoto/Thinkstock Get exclusive access to content from our 1768 First Edition with your subscription. Subscribe today

A flower having sepals, petals, stamens, and pistils is complete; lacking one or more of such structures, it is said to be incomplete. Stamens and pistils are not present together in all flowers. When both are present the flower is said to be perfect, or bisexual, regardless of a lack of any other part that renders it incomplete (see photograph). A flower that lacks stamens is pistillate, or female, while one that lacks pistils is said to be staminate, or male. When the same plant bears unisexual flowers of both sexes, it is said to be monoecious (e.g., tuberous begonia, hazel, oak, corn); when the male and female flowers are on different plants, the plant is dioecious (e.g., date, holly, cottonwood, willow); when there are male, female, and bisexual flowers on the same plant, the plant is termed polygamous.

A perfect flower with floral structures in multiples of three, Tulipa (tulip) has a three-lobed stigma, six stamens, and six distinct perianth parts.© Harry Haralambou/Peter Arnold, Inc.monster flower; titan arum; corpse flowerAn overview of the world’s largest blooms: the monster flower (Rafflesia arnoldii) and the titan arum (Amorphophallus titanum). To attract pollinators, both produce a rotting-meat scent, which has earned them the nickname “corpse flower.”Encyclopædia Britannica, Inc.See all videos for this article

A flower may be radially symmetrical (see photograph), as in roses and petunias, in which case it is termed regular or actinomorphic. A bilaterally symmetrical flower, as in orchids (see photograph) and snapdragons, is irregular or zygomorphic.

  • The radiate head of the treasure flower (Gazania rigens), a daisylike inflorescence composed of disk flowers in the centre surrounded by marginal ray flowers.E.S. Ross
  • Bilateral symmetry of the orchid (Vanda)E.S. Ross

Rose bush curling leaves

Thanks for contacting Ask an Expert about your rose question.

Wrinkled leaves can be attributed to a variety of causes. Early season attack by aphids can result in twisting and curling of new leaves, as the insects feed. The rose midge can also cause leaf curling, but usually attacks the flower buds, as well.

The disease powdery mildew can cause distortion of the leaves, though you might see whitish spots on the leaves, in that case.

Some common herbicides can cause twisted and misshapen leaves. If any weed control work was done around your condo, wind drift might be responsible.

Local weather conditions can also have an impact. Cool weather slows growth, then warm weather speeds it up, perhaps in an irregular pattern. Light frosts can have growth repercussions.

If the new leaf growth appears normal as the weather warms, I would put it down to an early season event and not as an on-going problem. If the leaves continue to be affected. Please send along a photo and we will attempt further diagnosis.

Have a great gardening season.

Dog rose

What does dog rose look like?

A thorny climber, dog rose has strongly hooked, or curved prickles, to gain a purchase as it weaves in between other shrubs and uses them to support its growth. It can grow up to 3m tall when well supported.
Leaves: on alternate sides of the stem, and divided into 2–3 pairs of smaller, toothed leaflets. Leaf buds can be affected by a gall known as robin’s pincushion. This looks like a ball of fibrous red threads and is caused by a gall wasp.
Flowers: large pink or white with five petals and many stamens. They have a faint sweet smell.
Fruit: striking red, oval, berry-like hips (15–20mm) form in small clusters. Each hip contains many hairy seeds.
Not to be confused with: the many species of wild rose found in the UK which are all very similar and difficult to identify. Roses are also commonly planted in gardens and some of these have escaped into the wild. One of these similar species is Rosa rugosa which flowers earlier than dog rose. Another is harsh downy rose (Rosa tomentosa), which has hairy leaves and fruit and straight prickles.

How to: remove rose suckers

Photo – photolibrary.com

Rose suckers can overtake a precious rose if you don’t act early.

Sandra Ross explains how to identify and remove them.

What is an understock?

Understock is the rootstock onto which a rose is grafted or budded. A good understock will grow in a variety of soil types and offer more vigour than roses grown from cuttings. Many roses are grafted onto ‘Dr Huey’ or Rosa multiflora. ‘Dr Huey’ is a vigorous, tough rootstock that grows well in hot dry areas, and can be readily budded or grafted. Its flower is deep maroon with a cluster of golden stamens. Rosa multiflora is an understock better suited to areas of higher rainfall, especially to Sydney and coastal NSW. Its flower is white. Both these understocks promote vigorous new growth, called water shoots, growing 2-3m in a matter of weeks during summer. These should not be confused with suckers.

]What is a sucker?

A sucker is a growth that originates from the rootstock of the rose, below the bud union where the rose was grafted. With bush roses, suckers may grow from rootstock below soil level. With standard or weeping roses, the suckers may grow from the trunk or stem of the rose. Foliage of a sucker differs from that of the budded rose, helping with identification. Suckers grow from a point on the rootstock where there has been an injury or trauma. Digging for weeds around a rose can cause such injury, so beware!

Why remove it?

If allowed to develop, suckers grow as long arching canes, with significantly more vigour than the rose itself. If suckers aren’t removed they will eventually take over the rose. Flowers produced from sucker growth are not the flowers of the rose variety purchased.

How is it done?

Suckers are best removed when the soil is moist. Scrape soil back to expose the sucker. Using thick gloves and brute strength rip the sucker off. With luck it will come off with a ‘heel’ (a piece of the older wood) and the point at which the sucker is removed from the rootstock will scar and ‘heal’. Suckers are more easily removed when new. If you wait until they are several years old and have had a chance to establish, it is a difficult task and you may not succeed. Cutting the sucker off will encourage more suckers to grow.

Exceptions

Wild roses and some old heritage roses are not grafted but instead are grown from cuttings on their own roots. Suckers of these roses are identical to the parent plant and can be dug up and transplanted when the rose is dormant.

Tetx: Sandra Ross

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