Overview:
Crops are mainly at the late flowering stage (GS 4,9) with most pods now set (GS 5,6-5,9). There are some backward crops
with weak, pigeon grazed plants which are at the early to mid flowering stage (GS 4,2-4,5). Phoma leaf spot is still
active at mid plant level and its incidence is still high in the south and east. The first stem cankers and phoma stem
lesions are now present and these will continue to appear and increase in severity up to harvest. Light leaf spot has
been much less important than usual this season and is only occasionally being reported on the upper leaves and stems.
Sclerotinia germination has been very high this year in the south and east and if problems are going to occur, plant
infection will soon be evident. Very heavy rain may have had a beneficial effect by washing petals off the leaves thereby
reducing the risk of infection. Levels of alternaria appear to be low at present, but it can increase rapidly given warm
showery conditions after flowering.
Pollen beetle damage has caused considerable loss of flowers, particularly on backward crops. Crop lodging occurred in early
May following very wet conditions in Lincs and adjacent counties. Lodged crops are particularly at risk from alternaria attack.
Final decisions on fungicides are now required on crops that are still flowering strongly and in crops that have lodged.
North:
Crops are generally vigorous and near the end of flowering (GS 4,7- 4,9). Phoma leaf spot is still present, but it is
usually confined to only a few spots on leaves at the mid-plant level. Stem canker and phoma stem lesions maybe found
but their incidence is still low. Where light leaf spot has not been well controlled, there are likely to be some stem
lesions and early pod infection is well established on the upper leaves. Downy mildew has increased over the last month
and is easy to find on the lowest leaves. With continuing showery conditions it can also cause large blotches on the pods.
Sclerotinia has been more prevalent in the north than in other regions in recent years. The fruiting bodies of sclerotinia
are still active and flowering crops are still at risk if the weather remains unsettled.
East:
Many crops are at the late flowering stage (GS 4,7- 4,9) with most pods set, but in some areas late crops are struggling
to survive pigeon and pollen beetle damage and are at early to mid flower (GS4,2-4,5). Severe crop lodging is causing
concern in some localities. Phoma symptoms are very easy to find on the middle leaves and large white or brown leaf spots
are present on most plants in high risk areas of Cambs. and Northants. Some light leaf spot is being reported, but levels
are generally lower than other regions. The Reference crop at Terrington received a second fungicide on 15 January and this
still appears to be giving some phoma spotting and it has increased leaf retention. Some small phoma stem cankers are now
present, notably where there was phoma spotting in late October/November.
Downy mildew has become more active over the last month and is expected to spread up the plant if conditions remain cool and
showery. Sclerotinia stem rot symptoms should appear soon if there are going to be problems this season. To date only leaf
symptoms have been found. Alternaria is present at low levels in some crops, but may still cause problems in lodged crops.
West:
Crops are generally near the end of flowering (GS 4,7- 4,9) with most pods set. Plant size is variable within crops where
germination was uneven. Phoma leaf spot remains active and is present at moderate levels in some crops. Grey leaf spots
caused by Botrytis are common where petals have stuck to the leaves in considerable numbers. The fungicide treated area
reference crop has suffered more pigeon grazing than the untreated area and is only at mid flowering (the untreated crop is
at the end of flowering). Direct comparison of treated and untreated records are not apprpriate in this case. Stem cankers
are present and there were more on the small treated plants than on the larger untreated plants. Is this a consequence of
pigeon damage reducing leaf size? Light leaf spot symptoms are still detectable, but its incidence is generally low.
Downy mildew is active on the lower leaves at the moment. Sclerotinia has historically been an important disease in the
west Midlands area and fungicide treatment should be considered on farms with a history of problems on crops that are
still flowering strongly if the weather continues to be unsettled.
South West:
Most crops are at the late flowering stage (GS 4,9) and there has been considerable petal sticking on leaves. This has
resulted on botrytis leaf spotting becoming common. Some recent phoma leaf spot activity has occurred, but its severity
is generally low and declining. Light leaf spot symptoms have appeared recently on stems in the reference crop and
further symptoms could still be incubating after infection in early May. Downy mildew has shown increased activity
on the leaves and might yet spread to pods in crops with dense pod canopies. White leaf spot should also be detectable
in its traditional locations in Somerset and Dorset - it produces black pod symptoms that are not easy to distinguish
from alternaria.
Decisions to apply a fungicide to control sclerotinia and pod diseases will probably be required over the next 2-3 weeks.
South East:
Most crops are at the end of flowering with good pod set (GS 4,9, 5,9). Petals are sticking in
considerable numbers and both botrytis and sclerotinia leaf infection is evident. A few sclerotinia
stem rot lesions are now being found. Phoma leaf spotting is still detectable at mid-plant level. At
the Reference site, light leaf spot has now spread to stems. Downy mildew is generally showing rather
weak activity on the lower leaves, but could start to affect pods if showery conditions continue.
Alternaria is still at low levels but there is still time for it to affect the pods particularly if
there are thundery showers.
There is still some air-borne spore production by sclerotinia and fungicide treatment may still be
worthwhile on late crops that are still flowering strongly.
Threshold for fungicide use:
Farms with a history of sclerotinia problems should consider a fungicide treatment in crops still at the mid-flowering stage.
Reports on the germination of sclerotia of Sclerotinia are available on the Internet at www.agricentre.co.uk. An easy to use
Sclerotinia Guide is available on the HGCA website (www.hgca.com) and this allows weather and crop factors to be combined to
identify risk.
There is a high disease risk in lodged crops and a broad-spectrum fungicide treatment should be considered where no fungicide
has been applied during flowering.
Choice of fungicide will be influenced by the threat posed by other diseases present in the crop, particularly light leaf spot
and alternaria.
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delivered to the industry by HGCA
This website was last updated on: 07/08/2008
© Crown Copyright Central Science Laboratory 2007
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All risk predictions published by CropMonitor are provided in good faith and are NOT a substitute for
rigorous fieldwalking in combination with advice from BASIS qualified persons. CropMonitor accepts no liability
for crop loss or damage resulting from the use of CropMonitor.
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