CROP CRACK - 10.03.07
By WENDY FEARON
Clarendon Agricare
According to samples taken over the last couple of months to access
leather jacket numbers, populations are extremely high. Despite the
predictions of a serious grub threat, blanket insurance spraying is
not recommended. Experience has shown that grub populations can be
extremely variable, not only from area to area but also within an
area and from field to field on the same farm. Consequently, even in
years of high predicted risk, there will always be some fields where
conditions are less favourable for leatherjacket survival and which
therefore contain lower levels of infestation. Hence even where past
history of problems may suggest that fields may be at risk from
leatherjacket attack, it is essential that some form of assessment
of leatherjacket infestation is conducted prior to deciding whether
any insecticide application is necessary. Conducting such
assessments in early spring helps identify those fields at risk
before any damage has occurred.
If infestations are proved to be high, either in grass to remain
as herbage or in leys to be ploughed, a spray should be applied as
soon as ground conditions permit. Pre-ploughing treatments are more
effective than those applied once damage is under way in the
replacement crop. However, where grub densities prior to arable
crops are marginal for treatment, current advice is not to take
preventative action against the grub straight away but to wait and
monitor the brairding crops and treat only if necessary.
The population threshold for treating permanent pasture is one
million leatherjackets per hectare (100/m2). The threshold in spring
crops is 0.5 million leatherjackets per hectare (50/m2).
Fields with a history of leatherjacket damage should be monitored
for large numbers of rooks and crows feeding on the larvae. Risk
assessments and testing for the presence of leatherjacket larvae
will provide a good indication of fields that are most likely to
need treatment.
If treatment is justified use Dursban* WG at 1.0 kg per hectare
applied in 200 to 1000 litres of water. Control will be reduced if
temperatures are below 5oC as the larvae will move deeper into the
soil profile.
WINTER BARLEY
Crops range from early tillering up to pseudostem erect
stage. Rhynchsporium and net blotch are the most common disease
present on winter barley at present. A fungicide should be applied
as soon as ground conditions allow. Ground conditions are still
favourable for slug feeding activity and pellets must be applied
where damage is seen.
WINTER WHEAT
Due to the milder conditions over winter foliar disease is present
on most crops especially in crops of Robigus where Septoria tritici
is very apparent. Winter wheat should receive a T0 fungicide
application followed by T1 at GS31-32.
OILSEED RAPE
Most rape crops achieved good establishment over the autumn and
winter, but bare patches are now appearing in some crops due to
clubroot. Wet soils coupled with the mild autumn are the reasons for
this outbreak. Light leaf spot is now appearing in some crops and it
is advisable to apply a fungicide now rather than stem extension,
especially to crops which did not receive an autumn treatment. |
