April Week 4 2021
Leaf layer tested: Primarily leaf 4 or 5, but at some sites leaf 3
Summary: Prior to the rain arriving at the end of April, Septoria was detected on Leaf 5 at three of our sites, whilst leaf 4 remains clean of disease at all sites.
Levels are currently not concerning but the results highlight the risk Septoria tritici presents and the need to not let our eye off the ball despite prolonged cool, dry weather.
It is probably going to take several rain events to trigger a severe threat this season – so rain forecast for early May could be critical. We don’t have to look too far back to see the disease can suddenly ‘take off’. April and much of May during 2019 was dry, and Septoria tritici was barely detectable in Elation and Motown at our Callow, Herefordshire, trial site. But heavy showers in the last weeks of May saw DNA levels jump, with leaf 2 in untreated Elation recording DNA levels of 250 pg/ul.
The yellow rust situation is unchanged, although the disease has been detected on the newest leaf layer in Zyatt at one site.
With the ‘business end’ of the season upon us, rain in late April and more possible might signal a change in disease fortunes.
We have now moved to testing the top two leaf layers to build an understanding of disease levels across the plant. Results from the last week in April reveal that the newest leaf layer is clear of disease at every site but Septoria has been detected on Leaf 5 at both our western sites and also in Perthshire, Scotland.
At J P Clay Farms in Herefordshire, leaf 5 in both September drilled RGT Wolverine (5.3) and KWS Extase (8.0) is carrying the disease. It isn’t a surprise to see it higher in Wolverine, but it isn’t alarming at 1.020 pg/ul.
Both carried Septoria tritici on emerging leaves from February, peaking in mid-March at 4.261 pg/ul and 2.69 pg/ul respectively. But as new leaves emerged in the dry, breezy conditions of April so the disease fell away. CTM Gareth Bubb thinks the upturn is down to the recent run of cool nights and mornings dews.
Septoria tritici is also present in leaf 4 of Zyatt (6.4) as is yellow rust (5) at Water Lane Farm, Lancashire. A Septoria tritici reading of 0.885 pg/ul isn’t troubling Spunhill agronomist Paul Cawood. At the same site early September drilled Extase is also holding some disease on leaf 4. But again, light at 0.12 pg/ul.
Cold dry weather has delayed T1s across the country but crops will soon catch up and it is likely that the gap between T1 and T2 will be shorter than normal.
Yellow rust remains undetected on the two newest leaf layers at all of our National Snapshot farms.