Agriculture Reference
In-Depth Information
Table 19.1 Levels of resistance to honey fungus in garden
shrubs and trees
Plant species
Latin name
Resistance level
Maple
Acer spp.
Susceptible
Box elder
Acer negundo
Very resistant
Birch
Betula spp.
Susceptible
Box
Buxus sempervivans
Resistant
Cedar
Cedrus spp.
Susceptible
Cypress
Chamaecyparis lawsoniana
Susceptible
Cupressocyparis leylandii
Susceptible
Eleagnus
Eleagnus spp.
Resistant
Holly
llex aquifolium
Resistant
Privet
Ligustrum spp.
Susceptible
Lonicera
Lonicera nitida
Resistant
Mahonia
Mahonia spp.
Resistant
Apple
Malus spp.
Susceptible
Pine
Pinus
Susceptible
Cherry and plum
Prunus spp.
Susceptible
Laurel
Prunus laurocerasus
Resistant
Rhododendron
Rhododendron
Susceptible
Sumach
Rhus typhina
Resistant
Lilac
Syringa spp.
Susceptible
Tamarisk
Tamarix spp.
Resistant
Yew
Taxus baccata
Vert resistant
Figure 19.16 Fireblight on cockspur hawthorn
( Crataegus crus-galli )
rapidly. They are important in the conversion of soil
organic matter (see Chapter 13), but may, in a few
parasitic species, cause serious damage or losses to
horticultural plants. In hotter, tropical countries, bacteria
are much more common as the cause of plant diseases.
June to September, favour the spread. Natural plant
openings such as stomata and lenticels are common
sites for infection. Flowers are the main point of entry
in pears. The bacterial slime mentioned above is an
important source of further infections. Fireblight, once
notifiable nationally, must now be reported only in
fruit-growing areas.
Control . The compulsory removal of the susceptible
'Laxton's Superb' pear cultivar in the 1960s eliminated
a serious source of infection. Preventive measures
such as removal of badly infected plants to prevent
further infection, and removal of hawthorn hedges
close to pear orchards, help in control. Careful pruning,
60 cm below the stained wood of early infection,
may save a tree from the disease. Wounds should be
sealed with protective paint, and pruning implements
should be sterilized with liquids such as those
containing citrus oils.
Fireblight ( Erwinia amylovora )
Damage . This disease, which first appeared in the
Britain and Ireland in 1957, can cause serious damage
to members of the Rosaceae family. Individual
branches wilt, the leaves rapidly turning a chestnut
brown (see Figure 19.16). When the disease reaches
the main trunk, it spreads to other branches and
may cause death of the tree within six weeks of first
infection, the general appearance resembling a burnt
tree (hence the name of the disease). Badly infected
plants produce a bacterial slime on the outside of the
branches in humid weather. On slicing through an
infected stem, a brown stain will often be seen. Pears,
hawthorn and Cotoneaster are commonly attacked,
while apples and Pyracantha suffer less commonly.
Life cycle and spread . The bacterium is spread by
bees as they pollinate, by harmful insects such as
aphids and by small droplets of rain. Humid conditions
and temperatures in excess of 18°C, which occur from
19
Bacterial canker of Prunus
( Pseudomonas mors-prunorum )
Damage . This disease affects the plant genus Prunus ,
which includes ornamental species, and fruits such as
 
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