Miscellaneous Pests - Pests of Ornamental Trees, Shrubs and Flowers - page 431

1146 1147

1146 Chrysanthemum nematode ( Aphelenchoides
ritzemabosi ) damage to leaves of Weigelia .

1147 Galls of northern root-knot nematode ( Meloidogyne
hapla ).

Migratory nematodes
Migratory nematodes usually feed externally on the
roots of plants, infestations most often occurring on
rosaceous hosts growing in light, sandy soils. Attacked
roots are gnarled and distorted, affected plants lacking
vigour and becoming distinctly stunted. Migratory
nematodes are also capable of transmitting important
plant viruses. Several groups of migratory nematodes
cause damage to ornamental plants. These include
dagger nematodes ( Xiphinema spp.) and needle
nematodes ( Longidorus spp.), which are often a
problem on rosaceous plants, and stubby-root
nematodes ( Trichodorus spp.), which commonly affect
not only woody plants but also bulbs.
Root-lesion nematodes ( Pratylenchus spp.) are also
classified as migratory species, although unlike the
other groups the adults and juveniles enter the roots of
host plants to feed internally; the nematodes also breed
within the host. Roots of infested plants develop short,
elongate lesions which afford ideal sites for the entry of
pathogenic bacteria and fungi; affected plants lack
vigour and wilt under stress. Roots often break off at the
point of damage, particularly once bacterial or fungal
rots have gained a hold. When conditions within the
roots become unfavourable, the nematodes disperse to
seek more suitable hosts. Root-lesion nematodes affect
various herbaceous ornamentals, including Anemone,
Begonia , Christmas rose ( Helleborus ), Delphinium ,
hyacinth ( Hyacinthus orientalis ), lily ( Lilium ) and lily-
of-the-valley ( Convallaria majalis ). More specifically,
the nematode Pratylenchus bolivianus infests Peruvian
lily ( Alstroemeria ), notably in the Netherlands but also
in England, and Pratylenchus penetrans is implicated in
the rotting of Narcissus bulbs, particularly in the

Netherlands and in the Scilly Isles. Other root-lesion
nematodes (e.g. Pratylenchus fallax and P. thornei ) are
of significance in mainland Europe on field-grown trees
and shrubs, especially Rosaceae; finally, Pratylenchus
vulnus , although a pest of greenhouse-grown roses
( Rosa ) in northern Europe, cannot survive outdoors
except in warmer climates.

Root-knot nematodes ( 1147 )
Root-knot nematodes ( Meloidogyne spp.) attack the
roots of various trees, shrubs and herbaceous plants.
Infested roots become distorted and develop rounded or
irregular galls. These galls measure anything from 1 to
20 mm across and often coalesce, causing considerable
distortion. The nematodes also exacerbate the
deleterious effects of pathogenic bacteria and fungi.
Root-knot nematodes are associated mainly with light
soils but most damage is caused under glass, particularly
in hot conditions where certain tropical and subtropical
species, e.g. the Javanese root-knot nematode
( Meloidogyne javanica ), have become established. Pot
plants such as Begonia , Coleus , Cyclamen , Gloxinia and
various cacti may suffer considerable damage, severely
affected plants appearing discoloured, lacking vigour
and wilting under stress. Northern root-knot nematode
( Meloidogyne hapla ) is a widely distributed,
polyphagous pest in northern Europe; it attacks many
different kinds of plant, including various ornamentals.
Root-knot nematodes invade host plants as second-stage
juveniles; these settle down to feed in the young roots
and usually reach maturity about 1-2 months later. Adult
females are translucent-whitish, pear-shaped and about
0.5-1.0 mm long. They may be found within the galled
tissue, often attached to a gelatinous sac that contains