It was expected that there would be a high take-up of SDHI chemistry in the fight against fungal diseases in cereals, but usage has been surprisingly low. Independent adviser Patrick Stephenson talks to Wendy Short

HISTORICALLY, Adexar (epoxiconazole and fluxapyroxad) could only be used on crops destined for the animal feed market, but a relaxation of the rules has recently been announced to permit its use on malting crops.

This will particularly benefit producers who routinely plant barley in the hope of achieving malting standards, but who are prepared to sell it as feed if the quality is disappointing.

However, he warned anyone taking advantage of the new option should be aware that its use is limited to one litre per hectare.

This “grow it and see” situation is not uncommon and it will be good to have an alternative to rival product, Siltra Xpro, as production problems might limit the availability of Siltra this season.

Both Adexar and Siltra have good rate flexibility, depending on disease pressure.

At the full recommended rate, Adexar is cheaper overall for winter barley.

Siltra is recommended for a 0.8 litres per hectare application, with Adexar at one litre per hecatare. On springsown barley, the rates would be up to 50 per cent lower.

The first application of a barley fungicide is normally the most cost-effective, so it is a good idea to use a robust rate for the first treatment.

A reduced rate can be used if a second application is required.

In the North of England, the ideal application time is likely to be the first and second weeks in April, at growth stage 30-31. This date range had been chosen because it is the period prior to rapid stem extension and before canopy closure. This timing should give the best yield response in barley.

SDHIs: wheat SDHI products are generally about 15 per cent more expensive than old chemistry, but with the forecast price of wheat currently standing at about £150/tonne, it should be worth the extra investment on most farms.

I believe take-up has been slow mainly because of grower perceptions.

Fungicides do not create yield – they only prevent yield loss. So in a year of low risk, the return on investment in SDHI products for wheat could be considered relatively small.

In a high or medium-risk situation, their use could potentially add two tonnes per hectare to the average yield and this would significantly increase profitability.

The total wheat acreage of a holding is an important factor when considering the use of SDHIs.

On a farm growing less than 100 acres of wheat, it is easier to make last-minute decisions on whether to apply a fungicide and which product to choose. A farm with a higher acreage may not always have the benefit of timeliness and the range of available options is likely to be more limited.

I would almost always advise growers with a large wheat acreage to spend a little extra and apply SDHI products – a yield response of 0.1-0.2 t/ha should be achievable, even in a low risk year.

An SDHI application will cost about £10-£12/ha more than a triazoles and multisite product, but should improve yields by approximately £30/ha year, assuming a wheat price of £150/tonne, even in a lowrisk year, although cost of application will have to be factored in.

At the very least, SDHIs act as an insurance policy.

They also help to offset the risk of chemical resistance to fungicides. This problem is increasingly threatening crop yields across the board and it is something that the industry needs to guard against in the future.

Varietal choice should also be considered when deciding whether to invest in SDHIs.

It is a question of balance.

A farm with 500 acres or less in wheat should plant a minimum of two varieties and preferably three. On a larger farm, a minimum of three different varieties should be chosen, with four the ideal number.

Varieties with a high rating for fungal disease resistance might mean that old chemistry can achieve good crop protection. These offer some flexibility when designing a treatment programme. It always adds interest to try a new variety and perhaps also choose one that has performed reliably under different conditions.

Third and/or fourth varieties should be selected for their ability to perform well in a particular region, or for other specific qualities.

These policies will help to spread risk.