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When rainfall occurs after initial infesta-
tion of small plants in the Western Cape,
plant growth is rapid and newly laid eggs
cannot survive in these plants. The first
infested leaves die off on the soil surface
(
Photo 3
on page 43).
No distinct damage to the plants is then vis-
ible. Several new infestation attempts may
occur during the next few weeks with lit-
tle effect. After heading, leaf growth slows
down and new infestation is possible. Since
the yield potential is fixed by then, grain
number and mass could be affected by a
heavy infestation.
Experience under irrigation
Field trials under irrigation demonstrated
that spraying could reduce the level of
leaf surface damage significantly per tiller
(
Graph 1
on page 42). However, this re-
duction was not reflected by a significant
yield increase on the sprayed treatment
(
Graph 2
on page 42).
As stated earlier, the level of damage during
the reproductive stages, is restricted only to
the grain size and number of kernels.
So what should the
producer do?
Early infestation in the Western Cape
tends to be severe, but as soon as
enough rainfall occurs, plants seem to
grow out of the problem.
The leaf miner is therefore recognised
as a pest, but not severe.
When heavy infestations occur and
you consider chemical control, apply
the chemical while larvae are still in the
leaves.
Since weather conditions fluctuate, and
notably so during the past few years,
the situation should be monitored, with
special attention to new infestations
later in the season.
During greenhouse trials, where both
flag leaf and the second leaf were re-
moved at flowering stage, yield reduc-
tion of 33% was measured. Thus, if both
leaves are lost to leaf miner, significant
yield loss could occur. However, to ex-
perience this level of damage, each
tiller in the field should lose both upper
leaves, a drastic situation not recorded
yet. The potential damage was extrap-
olated from the greenhouse data as
shown in
Table 1
on page 43. The table
illustrates an indication when it could
probably be worth spraying.
For further information on the problem, con-
tact Dr Goddy Prinsloo at
prinsloogj@arc.
agric.zaor 058 307 3435.
References
Adendorff, J. 2010.
The bio-ecology of the grass leaf
miner
, Agromyza ocularis (Diptera: Agromyzidae),
on wheat and barley in the North-
ern Cape Province, South Africa
.
MSc. Thesis: University of the Free
State.
on farm level
Integrated pest control
Leaf miner on wheat
Research was made possible through financial support from the Winter Cereal Trust and the ARC.