1 March 2002

Early spring spraying could pay with wheat

By Andrew Blake

MANY more winter wheats than usual could merit early fungicide treatment this spring, agree crop specialists. But opinions differ on the strength of recipe required at the T0 timing.

Widespread early drilling, the open autumn and relatively mild winter mean diseases are easy to find, says ADASs David Parish. "But dont over-react to levels you see in crops at the moment." Amounts of septoria visible now are a poor guide to later risk.

"If you are going through with a pgr on very susceptible varieties, like Riband and Consort, there may be a case for adding chlorothalonil, but no more than that."

Eyespot merits specific early treatment with Unix (cyprodinil) only if it has penetrated the outer leaf sheath. "But we need to be very wary because of the extra risk this year. It does tend to be under-estimated."

Mildew is obvious, but mostly dead, he adds. "I would use previous experience on farm rather than what you see in crops as a guide to the need for spraying.

"If you are growing an early sown susceptible variety like Claire on high-risk land such as the fens or sheltered valleys you might need to consider quinoxyfen, plus fenpropidin for knock-down if necessary."

Chris Bean, technical director for agchem distributor UAP, is confident that so-called T0 treatments, including strobilurins, will be worthwhile in many cases this spring. "Bear in mind that 70% of the crop was drilled before the end of September and 70% of those early sowings were with varieties like Claire and Consort which will need a lot of looking after."

Spraying at T0, which could often be justified from today (Mar 1), has two big advantages, says Mr Bean. "It makes inputs at T1 easier and perhaps cheaper and it eases the pressure if your T1 timing is delayed."

If 2002 mirrors 2000, a half-rate kresoxim-methyl based T0 spray should certainly be rewarding, he says. "The average response in our trials was 0.95t/ha."

However, Bob Mills of rival agchem distributor Banks Cargill is unconvinced of the value of early strob sprays. "I am very sceptical about applying strobilurins pre the traditional GS32 timing because they are mostly protectant.

"The natural inclination this year is to pile the inputs on, and we are probably looking at slightly more robust programmes. But look at it field by field."

A "sniff" of triazole and chlorothalonil for septoria and yellow rust or quinoxyfen for mildew could prove useful in with split pgr or manganese treatments, he acknowledges.

In Scotland, CSC CropCare agronomist Mark Ballingall anticipates more T0 spraying this season, albeit of triazoles and mildewicides. "Well keep the strobs for T1 and T2. There is a lot of septoria and mildew in Claire which needs damping down. We cant afford a false start if the weather delays T1s. Well tackle eyespot at T1."

Use soil type to help assess early eyespot treatment need, advises Nick Poole of the Arable Research Centres.

Crops on land with high surface humidity are more likely to get penetrating lesions, he says. "On chalk soils, which dry out quickly, eyespot never really penetrates."

In the end weather dictates whether a particular approach will pay, he adds. Although most T0 sprays paid off in 2001, many later treatments did not.

&#8226 For more on the weaponry available to fight cereal diseases this season turn to Fungicides Special on p64. &#42

First wheat fungicides

* Greater need for pre-T1 sprays.

* Beware of over-reacting.

* Mixed views on early strobs.

* Soil type influence on eyespot.

&#8226 Greater need for pre-T1 sprays.

&#8226 Beware of over-reacting.

&#8226 Mixed views on early strobs.

&#8226 Soil type influence on eyespot.