Dekalb trials manager, Anders Christensen reports on how OSR across the country is coping with the cold, wet spring from the company’s network of 25 trial sites in the second of our sponsored series.
Coping with the late spring
Thank heavens we saw such good OSR establishment and strong early development this season. It has stood the varieties we’re growing across our trial sites in very good stead in dealing with one of the latest springs in recent memory, allowing them to go into flowering retaining considerable potential.
Stem extension which we were just beginning to see at our earliest sown southern site near the beginning of February was brought to a grinding halt by the persistent cold, wet weather. Crops stood still for the best part of six weeks – not helped by ground conditions which seriously interfered with spring fertilisation and big flocks of hungry pigeons.
I dread to think what we’d be facing now if we hadn’t had come into February with some decent Green Area Indices and well-rooted, generally even 25-30 plants/m2 populations. It really does underline the importance of crops that establish vigorously and develop rapidly ahead of winter.
Coming into mid-April we are only just seeing the earliest varieties starting to flower at our most forward sites. Now well into stem extension, most crops are a good 10 days behind where we’d normally expect – let alone last year – regardless of their location. And those on heavy land, lying particularly wet and waterlogged are only just starting to extend, although at green bud.
These crops, in particular, clearly have a lot of growing to do as soon as conditions warm and dry-up enough for them to access their nitrogen. This lack of stature is just as well since ground conditions have yet to allow most of the spring fertiliser to be applied. It may also be of value in limiting the excessive vegetative growth which can compromise performance.
This season’s combination of late growth and pigeons means most of our trial sites certainly haven’t required specialist PGRs. The late pigeon grazing we’ve seen could be valuable in supporting the most productive, best-branched canopies too. But – and it’s a big but – it’s also likely to lead to more variable and prolonged flowering, with obvious implications for pollen beetle and sclerotinia risk.
Across our main replicated trials we’ve seen clear differences in the earliness of spring development between the 28 varieties we have in the ground – a character like to be especially significant in such a late season.
Traditional early season leaders, DK Extrovert and DK Exalte are continuing to show their superiority here over most other hybrids as well as the leading pure-line control included in our trial set. However, DK Expedient is proving itself to be noticeably quicker out of the blocks than either, with an average stem elongation after winter score of 8 on our 1-9 scale against DK Extrovert’s 7.2, DK Exalte’s 6.8 and an all-variety average of 5.6
This new introduction is showing the same edge of other varieties in our farm-scale strip trials with an average score of 7.5 against the all-variety average of 5.8.
As well as its notably vigorous establishment ability, DK Impressario CL is proving to be the fastest spring developer of the Clearfield varieties. Indeed, its 6.1 average rating puts it noticeably ahead of most non-CL varieties.
Not unexpectedly – as they have far less growth to put on – the semi-dwarfs remain the latest into stem elongation, only just beginning to move. Having said that, our low biomass hybrids, DK Secret and DK Serafin are standing-out as the fastest in their class.
Among the clubroot resistant varieties, DK Pliny is also proving to be a relatively fast developer while showing one of the lowest levels of early infection in our nine-variety clubroot understanding trial near Dundee.
Very little light leaf spot is yet apparent across our trials although, interestingly, where the disease is evident we are seeing no more of it on DK Expedient with its relatively moderate official resistance ratings than on either DK Extrovert or DK Exalte which are recognised as some of most resistant varieties.
Reduce flea beetle damage with white mustard
White mustard companion cropping can reduce adult cabbage stem flea beetle damage in the autumn and larval numbers in the spring, according to initial results from the Clearfield variety farm-scale strip trial study we’re running at three sites in central and eastern England this season.
In each case we’ve been comparing DK Impressario CL grown alone with the same variety at the same seed rate and three different inclusions of the white mustard which our previous and NIAB studies have suggested could be valuable in limiting damage from the pest.
Our late September/early October assessments of leaf short-holing and February counts of larvae/plant suggest an association between the level of white mustard and flea beetle damage.
However, in this and in our associated work with growers taking part in our wider commercial crop study with white mustard, we’ve seen the companion crop competing strongly with the rape, especially where Clearfield herbicides were not applied early enough. So the jury remains firmly out on the true value of the technique. This will only be apparent once all the trials have been harvested.