PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Disease cycle
Root knot nematode is a sedentary and endoparasitic
nematode (Fig. 137 below). Most nematodes are
found in the root zone from 5-25cm below the soil
surface. Only 2 nd stage juveniles can infect a
susceptible host. Life cycle in 25 days at 27 o C,
longer at higher or lower temperatures.
‘Overwintering’
Egg masses in soil, infected root debris, etc.
Dormant infections in roots of perennial hosts.
Spread
By infested flood or drainage water, infested
soil (on tools, machinery, containers, footwear,
soil deliveries), manures. Potting media.
Nematodes are often introduced into soil by
planting seedlings, cuttings, tubers or young
plants already infected with root knot.
Purchased plants.
By movement of nematodes through soil,
under optimum conditions this may not be more
than a few centimetres each season.
Infested crop and weed debris.
Conditions favouring
Warm moist conditions, but strains occurs
which prefer cool moist weather.
Sandy soils (contain air spaces for respiration).
Infested annuals may survive and produce
flowers if they never suffer from moisture stress.
Root knot can be a serious greenhouse pest.
Crops grown in soil. Should not be a problem
where soil-less media is used.
Continuous cropping with susceptible hosts.
Infested soil not treated in some way prior to
planting.
Depends on the stage of development of the crop
or its place in a cropping sequence. A well
grown crop can withstand a significant root
infection with nematodes, but a following similar
crop in the same ground will certainly develop a
damaging nematode infection while young and
will not produce a good crop.
Dormant stages or nematodes are stimulated into
growth when roots of a susceptible host plant are
close by.
Fig. 137. Disease cycle of root knot (Meloidogyne spp.). Males are 1.0-1.5mm
long and threadlike, females are pear-shaped and about 0.4-1.3mm long (adapted from Agrios, 1997).
Nematode diseases 269