Variety choice decides agronomy spend


After what has been a difficult year, the importance growers attach to a variety’s disease resistance is likely to increase even further. For many, the ability of a variety to resist disease has overtaken yield as the deciding factor when choosing what to sow.

KWS Siskin is a prime example. Its initial appeal came from its combination of barn-filling yield potential, wide drilling window that extends into the early winter, quality grain and excellent resistance to Septoria tritici, but its consistency has served to support its appeal. Consequently, it has been one of the most popular varieties for the past two years and grower feedback suggests its popularity may even increase this autumn.

For some growers, varieties such as KWS Siskin represent an opportunity to save on fungicide spend and, in the low-pressure years of 2017 and 2018 many achieved this without undermining performance. But with the curative activity of fungicides declining, just how sustainable or advisable is this policy when there is no means of recovering lost potential?

Good disease resistance is a useful management tool, especially when conditions mean spray timings are delayed, but it’s worth noting that the yield difference between untreated and treated almost only goes in one direction: up.

In KWS’ Cambridge June irrigated fungicide trials, KWS Siskin outperformed KWS Santiago regardless of the fungicide regime it followed. It still gave a positive return in investment, proving the maxim that fungicides are worth the spend, but the rate of response fell as application rates increased.

The low-input programme featured in the chart below featured only one SDHI. This is not a programme suitable for KWS Santiago or any other variety with below average Septoria resistance, but some have adopted this level of control for KWS Siskin. It should come with a warning: in a low disease pressure year, you may get away with it, but if pressure intensifies it will quickly be exposed as insufficient. The data shown may be from 2015 trials, however this pattern is replicated in trials from 2019. These results will be reported in due course.

Conversely, the standard programme featured two SDHI products at standard rates while the high-input programme kept to two SDHIs, but at higher application rates. The high-input programme would be sensible for any variety with poor disease resistance.

The standard programme is enough for a strong variety, such as KWS Siskin. The yield increase of 0.3t is worth £42 to enterprise gross margin (assuming wheat at £140/t) and is enough to justify the cost of a second SDHI.

The true benefit of a variety with better disease resistance, however, is most apparent when application timings slip.

The T3 application followed a standard programme under high disease pressure conditions with timings based on the optimum T2 and the optimum T2 + 10 days. The impact on yield of such a delay is startling. KWS Santiago and JB Diego suffered a yield penalty of around 1.5t/ ha. The varieties with better resistance still suffered a yield penalty, but at 0.5- 0.75t/ha it was far less severe. Septoria resistance is destined to be a vital part of variety choice for every farmer, not just those in higher risk areas of the South, West and North. However, it is also important to consider all disease resistances when making variety choice, especially rusts, which have been particularly lively this year.

While we will look for better Septoria resistance, we can be sure that for the time being the highest scores will come baring a small yield penalty. We can continue to grow the highest yielding varieties by lowering their risk to disease via drilling date, which is a very effective option. With concerns such as blackgrass and BYDV, drilling dates are often pushed back, however unpalatable that may be. In order to obtain maximum margin picking the right variety for your own farm situation could not be of more importance.