Field reports and observations from across the country indicate that septoria is the main threat facing wheat crops this spring.

Fuelled by a warm wet autumn, and a relatively mild winter, it is no surprise that Septoria tritici is already present in almost every wheat crop, irrespective of variety and sowing date.

Jonathan Blake
Principal research scientist
Adas

See also: Spray timing vital to beat winter wheat disease

Yellow rust has also been widely observed through the winter, although recently frosts have checked its progress.

This may only be temporary, as frosts were generally light in nature, especially in the South, and are unlikely to have removed the pathogen altogether.

Déjà vu for wheat disease threat

Last season, a mild wet winter and spring resulted in high levels of septoria and rusts in wheat crops.

Continued wet weather, particularly through April, May and early June, resulted in exceptional levels of foliar disease and average yield responses to fungicides were seen of about 4t/ha in HGCA Recommended List trials.

We’ve a long way to go, but so far 2015 looks to be shaping up compared with 2014.

What did we learn from 2014?

We have two main ways to combat diseases in wheat; chemical and cultural. In recent years, chemical rather than cultural control has dominated.

The widespread use of high yielding, disease susceptible cultivars in recent years has led to a dependence on fungicides to control Septoria tritici and yellow rust.

Following one the worst seasons for septoria in more than a decade, it’s hardly surprising there has been a shift away from the most susceptible varieties such as Kielder, Santiago and Oakley.

However, even the least susceptible variety Cougar saw a 2t/ha yield response to disease control in some HGCA Recommended List variety trials in 2014, so we are unlikely to kick the habit of using fungicides just yet.

Of the chemical control strategies for septoria, the multi-sites, azoles and SDHI’s are the three main types of chemistry.

The strobilurins, although largely ineffective on septoria, have a role within programmes as they still have good efficacy on rusts. 

© Tim Scrivener

Azoles are still an important part of disease control programmes. On yellow rust, the azoles (especially tebuconazole and epoxiconazole) are two of the most effective actives available.

On septoria, their almost continuous use over the past 20-30 years has led to insensitivity and a decline in their activity.

This means that in high-pressure situations, we are now unable to achieve good control with azole-based products alone.

The HGCA fungicide performance trials, which monitor changes over time, showed that in 2014, full rates of the two leading azoles provided 50-70% control in a protectant situation, and 45% control in a curative situation. 

These trials tend to underestimate curative activity, so in some circumstances control may be higher than this.   

The multi-sites, chlorothalonil and to a lesser extent folpet, were a key part of fungicide strategies in 2014.

These are just protectant products and their use throughout programmes significantly improved the control of septoria and increased yield.

There is universal consensus for their used at T1. Their inclusion at T2 divides opinion due to concerns over antagonism.

Usually at this timing we see they add far more than they take away, although under highly curative situations they have been known to reduce the activity of azoles and SDHIs/azoles on rusts and septoria in the past.

In 2014, SDHI’s played a crucial role. Their curative activity was invaluable on the more susceptible varieties, and strategies that did not include them at T2 where almost invariably compromised.

Their use at T1, however, still remains in question. In 2014, where they were included within an otherwise strong azole plus multi-site treatments on more susceptible varieties, yield responses of about 0.5t/ha were observed.

However, on less susceptible varieties under less extreme conditions, the benefit may be less than this, making the economic case for their use less easily justified.