Spring spraying: Planning care so essential to control rust

The payback in extra yield for rust control in varieties such as Oakley, which provides and will continue to provide some of the highest yields on farm, will be high.

That’s the advice of KWS agronomy consultant Bob Simons to growers currently contemplating their disease control plans for the coming months.

With 50 per cent of the UK wheat crop highly susceptible to yellow rust attack and several races of the disease present in the field, there will be sufficient inoculum around for all susceptible varieties to be at risk, as well perhaps as varieties currently considered to be less susceptible, says Mr Simons.

“There is always the possibility of something new around the corner. This coming season, expect to see rust anywhere,” he says.

Slowed disease

The recent big freeze will undoubtedly have slowed down disease development but it is unlikely to have destroyed yellow rust inoculum completely.

“What the recent cold snap has probably done is arrested sporulation, the disease will still be present in the leaf.

“All we’ve done is got ourselves a month’s grace. A good frost – minus 3 to 4degsC – for a few days gives you the same effect as a T0; it’s free but it’s very difficult to arrange delivery.”

While yellow rust may well survive the cold weather, brown rust is less likely to do so, agronomists believe. An early epidemic is not now expected this season.

However, T0 sprays will still be important, especially if crops are forward and dense by GS30, says Mr Simons.

Main target

T0 options for yellow and brown rust control are similar, although care is needed with product choice if the latter is the main target. A T0 spray is likely to provide three to four weeks cover, although this varies according to the extent of infection, crops growth rates, weather and variety.

According to Mr Simons, a high dose rate is not essential at T0 but a good triazole is.

T1 sprays should go on three to four weeks after T0 and, once again, advice is to opt for strong triazole chemistry if varieties are rated 5 or less for rust resistance. Strobilurins may be considered where disease has taken hold but bear in mind only two applications of a strobilurin may be made in a season, and their use may be more appropriate at T2 and T3.

The key message for T2 is “mind the gap” – the T1 to T2 interval should be no more than three to four weeks to ensure new leaf layers do not remain unprotected. Higher doses and stronger mixes may be required if disease control from the two earlier sprays has been compromised.

A T3 spray should be considered and a degree of rust activity factored in, adds Mr Simons.

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