Agriculture Reference
In-Depth Information
Oesophageal
bulb
Egg
Egg containing
nymph
Spear
Mouth
FEMALE
NEMATODE
(
150)
Intestine
Released
egg
Cyst containing eggs
in the soil survives
many years
Nematode larvae hatch
and enter potato roots
Autumn
and
Winter
Spring
(
15)
summer
LIFE CYCLE OF
POTATO CYST NEMATODE
Spring
Early summer
Male leaves root
and fertilizes female.
Female eventually turns
into a cyst and drops
from the root. (Magnified)
Male and female
nematodes induce
giant cells (stippled)
in vascul
a
r tissues
(shaded) of root.
(Magnified)
Female nematode begins
to swell. (Magnified)
Figure 18.29
Generalized structure of a nematode, and life cycle of potato cyst nematode
brown, while in the other species,
G
.
pallida
, no
yellow phase is seen. The significance of the species
difference is mentioned later in the control section.
Eventually, the female changes to a dark brown colour
and falls from the root into the soil. This stage, which
looks like a minute brown onion, is called the
cyst
, and
the many eggs inside this protective shell may survive
for 10 years or more in the soil.
Spread
. This nematode spreads, as cysts, with the
movement of infested soil, on boots and tyres. In
peat-soil areas, the cysts often travel along with the
wind-blown soil.
Control
. Several forms of control are available against
this pest. Since it attacks only potatoes and tomatoes,
rotation
is a reliable way of helping control. Growing
potatoes one year in five will often greatly reduce this
pest.
Early
cultivars of potatoes are lifted before most
nematodes have reached the cyst stage, and thus
escape serious damage. Some potato cultivars, such
as 'Pentland Javelin' and 'Maris Piper', are
resistant
to
golden nematode strains found in Britain and Ireland,
but not to
G. pallida
. Since the golden nematode is
dominant in the south of Britain, the use of resistant
cultivars has proved more effective in this region.
Growing a mustard crop to the flowering stage, and
then incorporating it into the soil as a '
green manure
'
encourages the increase in soil fungi that entangle
and parasitize the nematodes. No chemical forms of
control are available to the gardener.
Other nematode pests
Stem and bulb nematode (
Ditylenchus dipsaci
)
can damage onions (causing a soft puffy appearance
called 'bloat'). Affected carrots have a dry mealy rot.
Stems of beans are swollen and distorted. Narcissus
bulbs show brown rings when cut across and their
emerging leaves show slightly raised yellow streaks.
Weed control of the chickweed alternate host is
recommended. Rotation with resistant crops such as
lettuce and brassicas reduces pest numbers. Use of
planting material from infested soil should be avoided.
All these cultural methods help to reduce this pest.
Chrysanthemum eelworm (
Aphelenchoides
ritzemabosi
)
causes a blotching and purpling of
the leaves that spreads to become a dead brown,
V-shaped area between the veins of the leaves. The
lower leaves are worst affected because the eelworm
invades initially from the soil. This nematode also
attacks
Saintpaulia
and strawberries. For control, all
chrysanthemum plant debris should be disposed of.
Warm-water treatment of dormant chrysanthemum
stools (e.g. at 46°C for five minutes) is effective for
outdoor-grown plants.
