Bill Clark, newly appointed Commercial Technical director at NIAB TAG is warning against any complacency when it comes to yellow rust; with levels of active rust currently increasing dramatically across a wide range of varieties.
“The hard frosts of a few weeks ago have not diminished the progress of yellow rust – and it’s important to remember that is there is active rust in the crop, the crop is at risk. Getting on top of the epidemic as early as possible is key,” says Mr Clark.
“Oakley, still very widely grown because of its high yields, is frequently reported as having symptoms – no surprise there - but many other varieties are now also showing symptoms.”
The varieties most at risk that need checking are Conqueror, Einstein, Ketchum, KWS Podium, Solstice, KWS Santiago, Torch, Viscount and Warrior. These are in the UKCPVS Diversification Group 2b (DG), but also be on the lookout for Duxford and Gallant which, although in DG2a, are very susceptible. Mr Clark also advises growers to check the UKCPVS diversification groups for other varieties grown on-farm.
“Last season yellow rust was found at high levels in several crops of Warrior – the variety had previously been resistant to all yellow rust isolates. Samples tested by the UKCPVS at NIAB showed that we were dealing with a new race of yellow rust,” explains Dr Rosemary Bayles, principal cereal pathologist at NIAB TAG.
“The new ‘Warrior’ race is very like the earlier ‘Solstice’ race, but even more widely virulent. This means that it can infect all of the varieties which were at already at risk from the ‘Solstice race’, together with others such as Cordiale, Grafton, Timber and, of course, Warrior itself. The critical question for the coming season will be whether any currently resistant varieties will also turn out to be susceptible to the new race.”
Infection has already been widespread this season on many of the known susceptible varieties, but the UKCPVS has also had samples from some lower risk varieties such as Claire, Invicta and KWS Target. However, Dr Bayles explains that this does not necessarily mean that there are yet more new yellow rust races about.
“These varieties are known to be susceptible at early stages of development to existing races. This is true for many DG1 varieties with resistance of the adult plant type, which does not kick in until around early stem extension,” says Dr Bayles.
Mr Clark stresses that active rust at this stage means you still have to act. “Don’t wait for your next ‘normal’ timing – and don’t get hung up on T0, pre T1,T1 and so on. Just get in there as soon as you see active rust. With these very susceptible varieties the disease can quickly get away from you – particularly in the east. Even high doses at T1 will not always recover a situation gone wrong,” he advises.
NIAB TAG advises growers to check all high risk varieties before deciding on T1 treatments – and even varieties with high disease ratings should be checked for any possible new races by sending samples to NIAB for testing. Rust on these varieties may not develop, but could pose a threat to other varieties on the farm.
“Triazoles and strobilurins are the fungicides of choice at this early stage. A triazole plus strobilurin will give you both good eradicant and protectant activity,” says Mr Clark.