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Augustus 2018
92
Impact of
weeds
and
nematodes
on crop production
T
he role of weeds as hosts of other pests affecting crops
does not only have an indirect effect, but also has an eco-
nomic impact on crop production. Weeds serving as pest
hosts in the absence of crop hosts are reservoirs for those
pests, maintaining pest populations, which are available to attack
crops when planted. Plant-parasitic nematodes cause tremendous
yield loss on most cultivated crops worldwide. In South Africa, the
root-knot nematodes,
Meloidogyne incognita
and
M. javanica
in
particular, have been declared economic pests of most crops with a
wide host range, including weeds.
Three on-farm experiments were conducted during the 2015/2016
growing season in three provinces (Potchefstroom, North West
Province; Kuruman, Northern Cape and Mbombela, Mpumalanga) to
evaluate the host efficiency of 20 weed species that commonly oc-
cur in production fields against two common
Meloidogyne
species.
Two weed species, viz.
Hibiscus trionum
and
Tagetes minuta
, were
used as the susceptible and poor-host standards. All three on-farm
experiments had randomised complete block designs (RCBD), with
each weed species entry being replicated four times.
A natural
M. incognita
population existed at the Potchefstroom
site, the Kuruman site had a natural infestation of a monoculture
M. javanica
population, while at Mbombela a natural infestation
of a mixed
M. incognita
and
M. javanica
population existed. Trials
were terminated at 60 days after planting, randomly selected plants
were sampled and taken for extraction.
Outcome of on-farm experiments
Meloidogyne
spp. dominated in root (5 g and 50 g) and soil (200 ml)
samples obtained from the three on-farm experimental sites. Al
though other plant-parasitic nematodes such as
Pratylenchus
spp.
and
Hoplolaimidae
were also present in 5 g root samples and
the latter species as well as
Criconema
and
Tylenchorhynchus
were found in 200 ml soil samples, their population levels were rel-
atively low and warrant no further discussions for the purpose of
this study.
At Kuruman,
Solanum retroflexum
was the most susceptible weed
to a
M. javanica
population, while the same was evident for
H. trionum
at Nelspruit, where a mixed population of
M. incognita
and
M. javanica
occurred and at Potchefstroom, where a popula
tion of
M. incognita
was present. Results from this study indicated
that certain weed species are highly susceptible to root-knot nema-
todes and should be removed timeously and effectively to prevent
increases in population levels of root-knot nematode pests in the
fields of producers.
Cognisance
Since
Meloidogyne
spp. was maintained in roots of all the weed
species tested, none of them were immune to either
M. incognita
,
on farm level
Weeds / Pest hosts / Root-knot nematodes
Integrated pest control
Nancy Ntidi,
ARC-Grain Crops, Potchefstroom
1a
1b
2a
2b
1a and 1b: On-farm experiments.
2a: Roots of
H. trionum
infested with root-knot
nematodes.
2b: Roots of
C. carinatum
infested with root-knot
nematodes.