Warning as wet set to foster diseases

SARDI pathologist Hugh Wallwork warned attendees at the GRDC grain research update in Adelaide on Tuesday that there would be a lot of volunteers in paddocks because of continuing rain, which could increase the threat of rusts and powdery mildew.

“There isn’t much stem rust out there because of last season, and the colder weather has helped to keep stripe and leaf rusts under control, but that doesn’t mean it won’t build up quickly,” he said.

Dr Wallwork said septoria was also spreading with the strong uptake of Mace wheat, which was susceptible.

“Being such a good season last year, the threat will be a lot higher this coming year, particularly if there is frequent rain during the season,” he said.

Dr Wallwork said there were few wheat varieties that were strong against septoria – Kord and Cobra were best at mildy susceptible.

“It is a weak link in the system,” he said. “The best varieties for leaf rust resistance are Cutlass, Cobra, Clearfield Chief and Shield, while Kord, Scout and Trojan were MS. 

“Mace and Scepter are MS-S – so that could be a real problem if fungicides are not managed well.”

Dr Wallwork advised those growing new wheat variety Scepter to be careful.

“Last year, Mace growers used a lot of fungicide to control stripe rust, which helped keep leaf rusts under control,” he said.

“Scepter may have more stripe rust resistance than Mace, but then that leaf rust control could be lost, plus Scepter is more susceptible to powdery mildew.

“So if you do move into Scepter, keep that fungicide control up as if you were growing Mace.”

Dr Wallwork said powdery mildew was of concern as it could survive on stubbles.

“It doesn’t need the green bridge,” he said. “But if there is a green bridge, it will build up earlier and cause more of a problem in autumn.”

Dr Wallwork said these factors made the Free for February green bridge campaign important.

“Growers need to ensure everyone controls that summer green bridge in a narrow period of time,” he said.

“A staggered approach allows pathogens and pests to jump from one farm to the next, not providing a really good break.”