More second wheats could mean more take-all this season, Mike Abram hears

Favourable conditions in 2007 for take-all inoculum build-up could potentially leave many second wheat crops at risk from the disease in the coming season, says Richard Gutteridge of Rothamsted Research.

Tests over the winter on 220 field plots showed the proportion of roots infected ranged from 35% to 95%, he told a Syngenta-organised press briefing. “I haven’t picked up inoculum so high, so consistently.”

Conditions over the past three years had all contributed, with 2007, in particular, being “a cracking year” for build-up, he said. “Inoculum starts to build from May, and when soils are moist and it is not too hot, like last year, it can increase rapidly.”

Last season’s wet summer also made for a longer growing season, allowing more build-up, and delaying harvest, so take-all could pass more easily into the next crop.

“Late harvest is just like early drilling – you get a short interval between one crop and the next. Last year, we were picking up pockets of severe take-all. This year, you’ll probably find over a whole field it will be more general.”

Early nitrogen was one precaution growers could take, he said. “It will help kickstart crops into putting down more roots and ensure more tiller survival.”

Applying strobilurin fungicides, such as Amistar (azoxystrobin) could also help, although effects were variable, he noted. Trials had shown moist soils at application helped improve control with the product. “Where we had irrigated the trials it gave quite good control – it was worth having.”

It also gave an additive effect to where take-all active seed treatments had been applied. In a second wheat trial the combination of Latitude (silthiofam) seed dressing and Amistar foliar treatment reduced take-all index (a measure of extent and severity) from 75% to 44% with a 1.8t/ha yield response.

An even greater 3t/ha response had been seen where wheat had been grown as a third cereal, he said. “I’m not saying you will get that every time, but the potential is there given the right conditions.”

Adding a strobilurin at T1 would also be one of two potential strategies growers could use to combat rust, Jonathan Blake of ADAS said. “They add persistence and protection.”

The other strategy would be to use a T0. “Whether you need to do both will depend on how bad the rust is,” he said. “The key is to keep it under control while it isn’t a problem. Trying to control brown rust after it has established is very difficult.”