PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
OVERWINTERING,
OVERSUMMERING
In warm climates on perennial hosts, generations will overlap and so there is often no
‘overwintering’ as such.
Hosts, weeds
HOST PLANTS
Nematodes may ‘overwinter’ as dormant infections in the roots of perennial hosts, eg
bulbs, weeds. Stem and bulb nematodes may survive quite well in bulbs either in the
soil or in storage. In some instances the nematodes clump together to form ‘nematode
wool’ on the outside of bulbs in storage. The nematode wool looks like cotton wool
and in this form the nematodes are highly resistant to adverse conditions, eg drought.
SEED
Nematodes may survive for years in seed, eg seed-gall nematode of wheat.
Seeds
Root debris/soil
SPREAD
Infested soil
Infested manure
H 2 O
ALTERNATE HOSTS
Nematodes with a wide host range can survive on alternate hosts or weed hosts, eg root
knot nematode.
ROOT DEBRIS AND SOIL
Nearly all nematodes can survive as egg masses in infested plant debris and in soil
for years in the absence of a suitable host. The population of surviving eggs will
decline steadily over a period of months, so that at the end of a prolonged absence of
hosts the population may be very low.
In soils where annual crops are grown, eg vegetables and flowers, soil-inhabiting
nematodes with a wide host range, eg root knot nematodes, have no difficulty
surviving until the next crop.
Leaf nematodes can survive in leaf debris in the soil.
Wheat seed gall nematode (Anguina tritici) as 2 nd stage juveniles can survive for
decades in a dry dormant state.
INFESTED SOIL
Infested soil may be spread on tools, machinery, containers, footwear and in soil
deliveries. If healthy plants are planted into infested soil, nematodes move from the soil
into the healthy plants. Soil eroded by water or in mud. Soil-inhabiting nematodes and
fungi may be transported in dust.
INFESTED MANURE
Infested manure may be spread on animal's feet and in manure deliveries. Nematodes
in infected produce, eg potatoes, if fed to stock can pass through their digestive system
and be eliminated in their excreta.
WATER
Irrigation water or rain can splash foliar nematodes onto adjacent plants and facilitate
spread from plant to plant if leaves are touching. Flood or water in drainage channels
can carry nematodes to areas distant from the site of the original infestation.
Nematodes can spread from pot to pot via drainage water; this can be prevented by
placing pots on wire mesh. Foliar or leaf nematodes move easily up stems and across
leaves in a thin film of water, spread by water splash, on tools and by staff.
INFESTED SEEDLINGS, PLANTS, TUBERS
Nematodes are introduced into new areas by planting infested seedlings, plants,
nursery stock, tubers and bulbs. Golden nematode of potato spreads on infected tubers.
Seedlings, plants, etc
INFESTED CROP DEBRIS, WEEDS
Root knot may spread in debris from
infected crops and weeds.
Infested crop debris
MOVEMENT OF NEMATODES THROUGH SOIL
Under optimum conditions this may only be a few centimetres, certainly no more than
1 metre.
260 Nematode diseases