Will it be another rusty year? How to avoid surprises in 2018!
8 May 2018
Ben Freer, BASF
The remarkably early appearance of brown rust last year was a surprise that just underlines the need to be ready for any eventuality and makes growing wheat a constantly changing challenge.
For the past few seasons we have got used to yellow rust and its ability to outwit the plant breeders’ resistance ratings by mutating into different strains and popping up in unexpected varieties.
Yellow rust is well suited to the UK climate; it enjoys the cool conditions of a typical British summer!
In the spring, particularly in cool moist weather, the fungus starts to grow and produces active sporulating lesions.
Temperatures of 10-15°C and a relative humidity of 100% are optimal for spore germination, penetration and production of new, wind-dispersed spores.
The fungus is generally inhibited by temperatures over 20°C although strains tolerant of high temperatures do exist.
This disease is not normally a problem early in the season and usually only makes a “cameo appearance” in the south-east of the country in late summer.
Warmer temperatures encourage the disease, typically between 15°C and 22°C, and overnight dews are needed for sporulation and spore germination.
Consequently, brown rust epidemics have normally occurred during mid to late summer in the UK with dry windy days which disperse spores, and cool nights with dew, favouring the build-up of the disease.
2017 season epidemic
What was interesting about last season is that with the cool, dry spring following a mild winter, yellow rust was easily found and largely dealt with by T1. Then in mid-June we basked in high temperatures which in some parts reached the mid 30s °C.
These temperatures are just what brown rust loves and by the time we were all looking at variety trials it was easy to spot the susceptible varieties!
Yellow rust was completely eclipsed by its brown relative.
So, the timing of the epidemic clearly demonstrated the protectant abilities of the T2 fungicides (particularly where a T3 had not been applied).
I have spent much of my career trying to avoid overreacting to the previous season and trying to convince myself and others into encompassing a greater number of previous seasons into my fungicide strategy!
Clearly the 2017/18 season has been very different to the 2016/17 one. For a start we had a “proper winter” which will have reduced the inoculum levels of all diseases.
Secondly, we have had a “normal” spring – cool, very wet and generally frustrating.
This return to “normality” has meant that the one disease that revels in these conditions is Septoria – yes, the UK’s No.1 disease may have taken a backseat last year but it is back with a vengeance following the warm and showery conditions we are now experiencing! Worse than in Ireland I hear!
Choice of fungicide at flag leaf should therefore not be swayed by one disease or another but on its ability to cope with all eventualities.
That is why I will be recommending Adexar or Librax (plus chlorothalonil) at 1.25l/ha. They give unsurpassed, all-round disease control with Xemium providing proven Septoria control ably assisted by epoxiconazole (or metconazole) the best triazoles for yellow and brown rust control.
Why compromise control of one disease in favour of another when you don’t know what is around the corner? Then you will avoid nasty surprises! Choose a product with no compromises and one compatible with chlorothalonil to boot!