Agriculture Reference
In-Depth Information
(a)
(c)
(b)
Figure 1.10
Three invasive non-native plant species; (a)
Fallopia japonica
(Japanese knotweed) at Myddleton
House where E.A. Bowles fi rst planted it in his garden; (b) Clearing
Rhododendron ponticum
from a woodland,
note the lack of other plant species in the cleared area; (c)
Impatiens glandulifera
(Himalayan balsam) along a
river bank.
rootstock for grafting. It was fi rst recorded in the
wild in 1893 and has spread to woodland and
moorland, particularly on acid soils. The toxins in
its leaves mean that it is undamaged by insects
and can also harbour fungal diseases such as
Phytophthera ramorum
and
P. kernoviae
(see p.
44) which can spread to oaks, beech and nursery
stock.
X
Impatiens glandulifera
(
Himalayan balsam
) can
grow to 3 metres tall and is a serious problem
along riverbanks (Figure 1.10c). It was introduced
in 1839 from Northern India and grown for its
attractive pink and white slipper-shaped fl owers.
Its seed pods can project the seed explosively
up to 7 metres away and the seeds are carried
downstream to colonize new areas. The dense
stands shade out other species and it produces
more sugary nectar than any other European plant
species, attracting pollinating insects such as bees
away from native plants. When it dies back in late
autumn, it leaves riverbanks exposed and liable to
erosion.
Invasive species are particularly troublesome along
and in waterways where it is difficult to use chemical
control. Aquatic species such as water fern, Australian
swamp stonecrop, floating pennywort, Canadian
pondweed and parrots' feather are particularly
invasive. Others include
Buddleja
,
Cotoneaste
r, some
broadleaved bamboos and some exotic honeysuckles.
Gardeners can best prevent the spread of these
damaging weeds by knowing precisely which plants
they are buying, choosing non-invasive species and
disposing of plant material carefully. See 'Invasive
Plants' on the companion website.
The global trade in plants has also led to the
introduction of many new '
alien
'
pests and diseases
(see Chapters 18 and 19). Ash dieback (
Chalara
fraxinea
) is just the latest in a series of fungal diseases
affecting our trees.
'
Greenhouse gas
'
emission
, largely due to the burning
of fossil fuels and conversion of land for agriculture, has
been identified as the major cause of global warming.
The fruit and vegetables we eat and the plants we
grow will all have a
carbon footprint
made up of the
