The recent snow may not have hindered its progress as much as expected warns ADAS researcher.
According to ADAS researcher Jonathan Blake the recent blanket of snow could have acted as a barrier against the damaging severe night time temperature and subsequent frosts, reducing the severity of the frosts on the levels of yellow rust inoculum at crop level – which could mean that the risk of yellow rust this season is still present.
"Whilst there is no doubt that the recent frosts will have halted the cycling of yellow rust in leaves, and caused some leaf loss in older leaves where any infection may have become established, there has also been less leaf loss where crops were covered by a blanket of snow as the snow may have acted as a barrier and protected the plant, and inoculum sitting on the leaves, against the lower temperatures," says Mr Blake.
"This means that the low temperatures will not have actually killed off as much of the yellow rust inoculum as would be expected at crop level, and based on previous conditions - the warm autumn and infections recorded before Christmas I would expect to see yellow rust infections in crops well before the T1 timing this season," he notes.
Mr Blake underlines that an important message for controlling yellow rust going forward in the spring, is the timing and frequency of fungicide applications: "A triazole at T0 will be important on the most yellow rust susceptible varieties," says Mr Blake. "This will protect the timing of T1, and subsequently the gap between T1 and T2; if the T1 goes on at the right time, then the gap until T2 is the 3-4 week optimum, but if the T1 goes on too early for example in place of a missed T0, the gap until T2 is too long and disease will creep in."
"Whilst yellow rust is a major focus this spring, it is also important to consider early season control of eyespot as some of the rust susceptible varieties that are drilled in large acreages also have weak eyespot resistance, for example Oakley, and were also drilled early increasing the risk," advises Mr Blake.
"Eyespot control at T1 alone is never complete, so it would be worthwhile thinking about a split treatment between T0 and T1. Our trials have shown that by using a good eyespot product such as Tracker (epoxiconazole + boscalid) at T0 and T1, it is possible to get effective eyespot and yellow rust activity early on."
"At T1 it may be necessary to include products with additional Septoria activity. Both ADAS and HGCA Fungicide performance trials in 2008 and 2009 have shown Brutus (epoxiconazole + metconazole) and Ennobe (epoxiconazole+ prochloraz) to be leading azole mixtures on Septoria, and ADAS trials have proved them to be effective partners to Tracker at T1," says Mr Blake
