Last season’s HGCA fungicide performance trials have revealed previously unseen strengths and weaknesses of some active ingredients in controlling key wheat and barley diseases.

Spring 2014 was preceded by an open autumn and mild winter, resulting in crops coming into the spring carrying considerable foliar disease inoculum.

Septoria and yellow and brown rust tested commercial wheat fungicide programmes to the limit and barley growers also experienced high levels of rhynchosporium, net blotch and brown rust.

See also: Fungicide resistance could slash farm profits

Stuart Knight, Niab director of crops and agronomy, explained that this mix of diseases had provided some “tremendous” data and uncovered differences between fungicides that hadn’t been noted before.

“With the well-documented decline in azole activity, people are now very interested in what the other active ingredients can bring to the party.

“Product choice needs to be adapted to the disease pressure faced and growers should make use of all the available tools in the box,” said Mr Knight.

Commercially available fungicides are assessed each year for performance in keeping disease out of crops (protectant activity) and also their ability to cure or eradicate disease (eradicant activity).

SDHI/azole co-formulations such as Aviator and Adexar, along with tank-mixed Vertisan + Ignite, remain the most effective septoria treatments for wheat growers, both as protectant and eradicant options.

Individually, they remain closely matched after disease assessments. But Mr Knight noted that when considering yield response, the tank mixture of Vertisan and Ignite was not as strong as the others.

“Although disease control looked very similar, in some 2014 trials there was a faster decline in green leaf area, pointing towards less persistency from that treatment,” he added.

Multi-site active ingredients – particularly chlorothalonil – proved their worth against septoria, with half-rate Bravo outperforming straight azoles as a protectant and for yield response.

“It is still doing a very good job, but the other multi-site folpet is not performing quite to the same level,” added Mr Knight.

Rust control

It was a problem rust year for wheat growers and the HGCA trials also highlighted some differences between fungicide treatments for controlling yellow and brown rusts.

The strobilurin product Comet “stole the show” for brown rust control, according to Mr Knight, wiping the disease out at just half of the full label rate.

Straight SDHIs Vertisan and Imtrex also performed well against brown rust and out of the SDHI/azole co-formulations, Aviator was slightly behind the other available options, but all still did a good job.

“But on yellow rust the straight SDHIs aren’t performing as well, with straight epoxiconazole product Ignite the most effective.

“With prothioconazole not as strong on yellow rust, you can see why Aviator is slightly weaker than the epoxiconazole-containing Adexar and Vertisan-plus-Ignite treatments against the disease,” explained Mr Knight.

Barley diseases

A similar portfolio of active ingredients was tested against barley diseases, although some with different product names and, again, differences were revealed.

Two straight SDHIs were used in the trials to assess their individual merit against rhynchosporium and Syngenta’s isopyrazam-containing Zulu proved weaker in 2014 than BASF’s Imtrex.

Straight SDHI Vertisan did not feature, but an SDHI/azole tank mix of Vertisan and Proline was weaker than co-formulations Siltra Xpro and Adexar, suggesting Vertisan is the weaker SDHI against the disease.

Siltra Xpro and Adexar performed well against rhynchosporium, both as protectant and eradicant fungicides.

“All the SDHIs are performing well against net blotch, althought Vertisan was inferior to Imtrex last season. Bontima is a similar match to other SDHI co-form products and brings a different mode of action into the programme with cyprodinil,” said Mr Knight.

Brown rust also made an appearance in barley crops in 2014, and at the HGCA trials site at Caythorpe in Lincolnshire, all the co-formulated SDHI/azole products performed strongly.

Single SDHI actives, azole Proline and strobilurin Comet also provided good control, but Mr Knight noted that yield responses were better when using mixtures.

“We also assessed brackling [buckling of the lower stem] and found there is a good link between the best disease control and reduced brackling,” he added.

Stuart Knight

Stuart Knight was speaking at the recent HGCA agronomists conference.