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.
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.
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.
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.
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.
