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Ornamental

 
                 
 
 
History
Growing roses throughout the year
Integrated pest management
References
Diseases
Pests
Fertilisers
 


Roses

Modern roses

The history of hybrid tea and floribunda roses

The original species of wild rose had a single flower with five (or in some cases four) petals and grew across all of the continents in the Northern Hemisphere.

The first garden roses probably first occurred in the Middle East, spread throughout ancient Greece and Rome, and eventually across Europe. These roses were in groups we now call gallica r oses, damask roses and alba roses.

In the Middle Ages roses were widely cultivated in monasteries, mainly for their medicinal properties. Over the centuries new varieties were produced, mostly from chance seedlings. By the eighteenth century gardeners, mainly in France, had started to select the most desirable seedlings. The speed with which new varieties of rose were created greatly increased after that.

Between the seventeenth and eighteenth centuries another group of roses was added in the form of centifolias (literally `one hundred petals'). These were beautiful, not only for their flowers but also their form and fragrance. With the arrival of this group the rose became the most prized of all garden flowers.

Around 1800 a small group of four China roses arrived in Britain. Little is known of their history but they did have one property that influenced the breeding of roses - their ability to flower repeatedly throughout the summer. It was not long before the China roses were interbred with the European roses. As the hybrid Chinas were interbred, repeat-flowering varieties started to appear and out of these seedlings came the Portland roses and the bourbon roses. Overlapping with the bourbon roses were two more groups called hybrid perpetual roses and tea roses. The origin of the tea rose name is obscure - it is either a reference to their scent resembling fresh tea leaves or to the tea chests in which they were imported from the East.

It was by crossing the hybrid perpetual rose with the tea roses in the latter half of the nineteenth century that the h ybrid tea roses were produced. The hybrid teas quickly became popular and have remained so to this day. In 1870s a French breeder produced a new group called polyantha roses. These produced small, rambler-like flowers in clusters. Polyanthas were then crossed with hybrid teas resulting in a new group called floribunda roses.

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Growing roses throughout the year

 

Winter

June, July and August.

  • Ideal time to plant bare-rooted roses.
  • Winter-prune established plants to remove dead and diseased wood. Prune the remaining growth down by approximately one-third of its height.
  • Spray the bushes and surrounding ground to prevent fungal spores from `over wintering' on the bush or in the ground. Chemicals that can be used for this are copper oxychloride, winter oil or lime sulfur.

Spring

September, October and November.

  • Mulch beds for weed control and moisture retention during drier summers. Use well rotted manure mixed with garden compost.
  • Start spraying for pests and diseases at leaf break and continue at 14-day intervals using either low-toxic organic or chemical controls.
  • Apply base fertilisers in September and three-month slow release fertilisers in October.
  • Start deadheading flowers as needed.

 

Summer

December, January and February.

  • Deadhead old flowers to encourage new growth and repeat flowering.
  • Irrigation: Roses do not like to dry out so maintain soils at field capacity during the hot summer months by watering roses heavily at least once a week. Don't wet the foliage. However, this can be beneficial in that it deters mites.
  • Remove weeds and hoe under rose plants as required. Apply three-month slow release fertilisers after the first flowering flush (usually at the beginning of January).

Autumn

March, April and May.

  • Continue deadheading old flowers.
  • Remove leaves from around the rose bushes to remove disease spores on old leaves.
  • Remove old or dead roses. Order new roses for planting in winter. Prepare planting sites by removing soil where roses have grown because rose roots produce chemicals that will inhibit the growth of rose seedlings and the roots of newly planted plants.

 

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Integrated pest management spray programmes

When developing an IPM or organic spray programme, one easily made mistake is to continue the old calendar spray philosophy but substitute `chemicals' with more user-friendly substances. Many factors need to be taken into consideration when managing the pests and diseases on your rose plants:

  • identify the pests and diseases present on the plants,
  • seek information on the life cycles of all the pests and diseases present,
  • identify any natural beneficial insects that are present,
  • seek information on the life cycles of natural beneficial insects present.

Weather patterns can also have a major influence on the occurrence of diseases.

Because most fungicides are preventive, the key period to control diseases is in the spring/early summer (September to December). By keeping infection levels low during this period, control is not as critical later in the season.

Rose varieties differ in their susceptibility to diseases so identify those that grow best and replace disease-prone varieties.

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Diseases

Fungal diseases present the biggest concern to the rose grower. Of the 13 different fungal diseases of roses listed in New Zealand (Pennycook 1989) six cause the most serious problems.

Listed in order of importance they are:

  • Rust Phragmidium mucronatum
  • Black spot Diplocarpon rosea
  • Powdery mildew Sphaerotheca pannosa
  • Downy mildew Penonospora sparsa
  • Grey mould Botrytis cinerea
  • Silver leaf Chondostereum purpureum.

Rust

Rust derives its name from the orange-brown spore masses that the fungus produces. Rust has been recognised since ancient times. The Romans considered the cereal rusts so important that they believed two Gods, Robigo and Robigus, were responsible for them.

The upper surface of leaves become speckled with yellow patches, which often run together. On the under surface there are correspondingly orange-brown spots. If stem infections are heavy, the stem may be ringbarked, resulting in die back of the upper portion of the stem.

The key to control is the early application of preventive fungicides from leaf break in spring and removal of all infected leaves and stems.

Black spot

Circular black spots up to 1 cm in diameter with fringed margins and in various numbers appear on leaves. A yellowing of a portion or all of the leaflet and then defoliation soon follows the appearance of spots.

The key to control is the early application of preventive fungicides from leaf break in spring. Remove all infected leaves.

Powdery mildew

Affects only the growing tips in dry/hot conditions during mid summer (January to February).

Control can be achieved by applying preventive fungicides to susceptible varieties at the beginning of January, before infection occurs.

A mixture of baking soda/mineral oil used as a preventive has been successful in controlling the spread of this disease.

Downy mildew

Affects old leaves lower down on the plant in cool/wet conditions during spring and autumn.

Spray in early spring and late summer.

Grey mould

Randomly affects flowers in cold/wet conditions. Can also infect the stems. Most infections occur in autumn on plants in shady areas.

Remove diseased flowers.

Damaged stems can be pruned off in winter.

Silver leaf

Randomly infects plants after winter.

A product called `Trichopel G' that contains soil fungi of Trichoderma spp. can be introduced into the planting holes of all new plantings of roses to prevent infection by this pathogen.

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Pests

Pests in order of importance:

  • aphids
  • two spotted mite.

 

Aphids

Monitoring can determine if there is a natural population of beneficial insects (predators of aphids) within the rose garden that might be eliminated by the calendar insecticide spray regime. Only spray with insecticides if aphid populations become too dense.

Some natural aphid predators that may be present include:

  • hover fly ( Melanostoma fasiatum)
  • lacewing ( Micromus tasmanian )
  • ladybirds ( Coccinella undecimpuctata and Adalia bipunctata
  • aphid parasitic wasps ( Aphelinus sp. and Aphidiidae sp.)

Two spotted mites

A number of steps can be taken to prevent mite populations from increasing to levels that require control:

  • use mineral oils to reduce over wintering populations,
  • wet foliage during summer watering,
  • use deterrent sprays (seaweed and neem oil),
  • climate (lower overall temperatures),
  • introduce predator mites.

Insect deterrents

Two natural chemicals with insect deterrent properties can be used with the fungal spray programme:

  • neem oil
  • liquid seaweed

These can be added to all spray mixes and can reduce the need for insecticides over the growing season.

Isolated populations of aphids and mites may occur where good coverage has not been achieved. These populations can easily be controlled by spot applications of insecticides.

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Fertilisers

Seaweed that is applied to deter insects also acts as a liquid fertiliser.

The following fertilisers can be applied before and during the growing season:

  • Base dressing in spring (September):
    • Gypsum
    • Dolomite
    • Potassium sulfate
    • Blood and bone
  • Side dressings
    • At the start of and after each flowering flush (early December to the end of February) use three-month slow release fertilisers.

 

Happy rose gardening!

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