The risk of disease development in oilseed rape canopies rises as humidity increases. High humidity encourages wet weather diseases, such as Botrytis and Alternaria, and these in turn will adversely affect seed fill and can cause yield loss through pod shatter.
"Humidity levels have increased significantly as the weather has been showery and the temperature has been warm. Many crops that did not benefit from a growth regulating fungicide this spring are too thick as a result of such a good autumn. Some of these thick crops have started to lodge and heavy rain will increase this problem even further," advises Diane Heath, Oilseed Rape Product Manager for BASF.
"These prevailing conditions will encourage Botrytis and Alternaria. Botrytis is already spreading, particularly on leaves that have suffered fertiliser scorch. It can be seen as a grey superficial fungal mould on any part of the plant that is damaged either through pest or mechanical or fertiliser damage. Alternaria is seen as small brown or black spots on leaves and pods, about 1 to 3 mm in size. Larger spots have distinctive concentric rings. It is spread by rain-splash in warm, wet weather," reminds Diane.
According to Diane, Compass provides cost-effective control against the spread of all these diseases through the canopy and keeps the canopy green for yield building. Targeted from 20% pod set onwards, Compass is recommended at dose rates between 1.5 and 2.0 l/ha, with the higher rate being used where Alternaria is the key target. The lower rate is also a useful top-up spray where a late stem extension fungicide has already been used in the crop.
Compass is compatible with a range of pyrethroid insecticides including Contest. These may be used at flowering but applications should be made in the late evening, early morning or dull weather when bees are not actively foraging in the crop. Local beekeepers should be advised of the intention to spray, concludes Ms. Heath.
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Compass contains 167 g/l iprodione and 167 g/l thiophanate-methyl formulated as a suspension concentrate, packed in a 5 litre pack. It is recommended in oilseed rape for the control of dark leaf and pod spot (Alternaria brassicae), grey mould (Botrytis cinerea), low levels of Sclerotinia stem rot and late light leaf spot (Pyrenopeziza brassica). Compass has protectant and systemic activity. It is recommended at a dose rate of 1.5 to 2.0 l/ha from mid flowering (20% pod set onwards) to the end of flowering. It has a harvest interval of three weeks and has no LERAP.
