PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Cause
A number of viruses have been associated with
roses in Australia including Apple mosaic virus,
Potato Y virus, Prunus necrotic ringspot virus,
Strawberry latent ringspot virus. About 40 viruses
and virus-like diseases affect roses worldwide
including aster yellows phytoplasma.
VIRUS DISEASES OF ROSES
Host range
The host range of each virus is different.
Apple mosaic virus and Prunus necrotic ringspot
virus, the commonest viruses which affect roses,
are mainly confined to Rosaceae, eg apple, Prunus,
rose, strawberry.
Symptoms
The disease is characterized by yellow patterns on
many or only a few leaves (Fig. 148). These
detract from the overall appearance.
Leaves. Symptoms are variable, eg
Chlorotic mottling. A yellow mottle
involving the minor veins of the leaflet which
may gradually spread to a general chlorosis.
Line patterns. Many lines or broad bands of
pale green or creamy tissue, ‘oak leaf’ patterns.
Veinbanding. A narrow band of yellow along
the entire vein network of the leaflet, an isolated
area of the leaflet or only around the margins.
Flowers usually appear normal.
General. Although it has long been thought that
‘mosaic’ has no general deleterious effect on rose
plants, recent work has shown that infection can
lead to a reduction in vigour and flowering.
Diagnostics. Different symptoms associated
with rose mosaic, and can often be mistaken for:
Herbicides injury, the chlorophyll has been
destroyed.
Nutrient deficiencies or toxicities, eg
iron deficiency on new leaves or magnesium
deficiency on old leaves (page 275, Table 54).
‘Overwintering’
In the canes, buds and roots of infected rose and
other host plants.
Rose ‘mosaic’
Spread
All viruses are spread by propagation
(budding and grafting) from infected plants or by
the use of infected rootstocks.
Apple mosaic virus is also spread by contact
between plants and possibly by pollen, its spread
in nature is not known.
Prunus necrotic ringspot virus is also
spread by pollen to seed and by pollen to the
pollinated plant, and may be by seed in some
species, but not by contact between plants.
Not by insects.
Conditions favoring
Vegetative propagation from infected plants.
Symptoms are often more pronounced during
spring and may disappear during summer.
Management (IDM)
Are you a commercial grower or home gardener?
1. Obtain/prepare a plan that fits your situation.
Rose mosaic is not considered a serious disease and is
usually introduced to a plant during grafting by the use
of infected rootstock, budding or grafting material.
2.Crop, region. Control measures will vary
depending on the crop, region or situation.
3.Identification, if there is any doubt, must be
confirmed by diagnostic tests in a laboratory (page xiv).
4.Monitor. Inspect crops regularly for diseased plants.
5.Threshold. There is a nil threshold for commercial
propagators and growers. Home gardeners generally
accept the disease.
6.Action/Control. Commercial growers should
remove infected rose bushes and plan to only use
disease-tested propagation material.
7.Evaluation. Review your program to see how well
it worked and recommend improvements if needed.
Continue regular crop inspections.
Control methods
To minimize losses in commercial plantings:
Cultural methods.
Plant virus-tested and healthy plants some
distance away from older infected bushes to
reduce likelihood of virus infection via pollen.
Sanitation.
Commercial rose propagators, growers and
nurseries should remove infected rose bushes.
Disease-tested planting material.
Only use virus-tested budwood and rootstock for
propagation, purchase virus-tested nursery stock.
Do not use virus-infected plants as a source of
budwood or rootstock.
Fig. 148. Rose ‘mosaic’ – symptoms on rose.
Left: Line patterns. Centre: Chlorotic mottles. Right: Veinbanding. PhotoDavid Olsen
Virus and virus-like diseases 291