With T1 fungicide applications well under-way, the focus of concern in wheat has switched away from the yellow rust which appeared to be endemic a few weeks ago, towards the septoria which, like Putin on the Ukrainian border, lurks menacingly waiting to invade – it’s not “if” – it’s “when”.
The worry this season is that the septoria sits on older leaves which are still alive, mostly upright and flapping about within the canopy, instead of being dead and flat to the floor as they would have been after anything that resembled a “normal” winter. The implications of this are that septoria’s usual method of spread – rain splash – may not be necessary to spread it around the canopy, because just like children with nits, direct contact with other leaves will be just as effective.
With this in mind, a robust dose of either prothioconazole or epoxiconazole plus SDHI – I include Boscalid in the SDHI group of course – is in my opinion the only route to take. Your choice of fungicide at this stage is critical to your harvest outcome, so don’t be tempted to save a couple of quid – if you let septoria get a foothold now you won’t get back in charge again this season.
Assuming that a crop isn’t at GS31 just because it is only 4-5 inches tall is a schoolboy error, but it’s one that’s made every year by an awful lot of people. This week I was in some Gallant – two fields which were drilled 6 days apart, a first wheat after spring beans & a second wheat – both being grown for milling. Visually, the first wheat is around 10 inches tall and the second wheat is around 5 inches tall. From a distance you could easily be forgiven for thinking that the first wheat is at GS31 and the second wheat still mid-tillering. The reality of the situation is, however, that both wheats are exactly the same growth stage – approaching GS 32 on the main stem and GS 31 on the lead tiller – the only thing that is the same about every season is that they’re all different.
In around four weeks time the awns will be widely out in barley and the flag leaf will be out on forward wheats. This is because of the phyllochron – the length of time it takes for each leaf to emerge, and which consists of in the region of (depending upon whose technical paper you read) around 75 growing day degrees (GDD) per leaf. If you accept that every degree above 8°C is one GDD, then if you get 10 days of 16°C, that gives you the required 75 GDD and therefore a leaf will emerge. If therefore, leaf 4 is out in your wheat as you read this, if it averages 18°C the next couple of weeks, it could be as soon as a week from today before leaf 3 is out, another week and it’s leaf 2 emerging, and another week then BINGO – the flag leaves will be out!
It now has everything to do with day length and temperatures, and absolutely nothing to do with the calendar, so ensure these crops are covered both from a disease control point of view and also from the growth stage cut-off timing for chlormequat if that’s what you’re using as a growth regulator. All nitrogen on winter wheat will have been applied by the end of this month, apart from protein dressings on the milling wheat.
In other crops, oilseed rape has grown so fast that stems have split – this could be an easy route in for sclerotinia, so choice of suitably active protectant fungicides will be critical once again this year.
Sugar beet is emerging well across the county with odd patches of skylark damage, first post-emergence herbicides were applied last week and the 2nd applications are underway as we speak on the earlier drillings – good to see beet fields emerging well – it’s been a couple of years since that happened last . . . !
Pea & bean weevil damage is widespread in spring beans, so crops should be monitored closely and bird cherry, rose grain and grain aphids are widespread and easy to find in spring cereals so barley yellow dwarf virus (BYDV) control measures should be put in place at the earliest opportunity.