2 June 1995

MATCH INPUT TO VARIETY

At Cereals 95 Morley Research Centre will apply the events theme of "efficiency through more effective management" to cereal disease control and pgr use. Charles Abel explains

FEW would deny that fungicides need matching to variety. The problem is deciding how to strike that crucial balance.

At Cereals 95 the plots prepared by Norfolk-based Morley Research Centre aim to provide some pointers. Central to the strategy is matching management to the inherent strengths and weaknesses of a variety.

"The breeders are trying to get genetic resistance to control disease. As they become successful we want to reduce fungicide use to take advantage of that," explains Doug Stevens, cereals specialist at Morley.

He reckons too many growers are failing to do so, leaving their production costs unnecessarily high. Fungicides applied before the second node timing are a particular concern. "Too many growers are just paying too high an insurance premium."

A trial at Morley last year showed the value of tailored inputs. The aim was to adapt fungicide inputs according to varietal strengths, so that yield was the same as plots which received a £95/ha (£38/acre) "Rolls Royce" fungicide programme, but at less cost.

Six of the seven varieties achieved that, with fungicide costs of £51-£24/ha (£21-£10/acre) and equal or greater yields.

"By making added use of varietal resistance in Hunter we cut fungicide costs to £24/ha with no yield loss. Beaufort is probably quite similar and fairly predictable. The difficulty is with a variety like Brigadier. It is relatively more disease resistant than Riband. But we still expect a massive response to fungicide. The fungicide response is there."

The difficulty is placing a value on improved disease resistance. "Hereward plagued us for years. In retrospect we tended to over treat it, because we werent confident it could hold diseases. And because it was a quality variety we treated the ear.

"Even though they were reduced rates, the results showed we were no better off than if we had sprayed at flag leaf only," Mr Stevens comments.

So how can growers get round that? "The key is local trials, by groups like ourselves and to some extent the breeders," says Mr Stevens. Those will show how a variety responds to disease pressure under local conditions.

On the Cereals 95 site Morley has established a winter wheat fungicide demonstration using four varieties and three fungicide strategies, as detailed in the panel.

One of the key issues being demonstrated is the use of fungicides before the second node growth stage. "We would expect to find the lower leaves greener in the plots which have a pre-GS32 spray. But will it bring a cost effective benefit?" he asks.

In his opinion it rarely does. "Unless there is severe eyespot, mildew or yellow rust in early spring theres no cost benefit in applying a fungicide before leaf three emerges – and that is usually about second node."

He admits that the policy depends upon the ability of the grower to hit the disease effectively at second node. "But too many farmers are paying too much for insurance.

It is not excessive brinkmanship to leave foliar disease control until GS32. Going in earlier is usually over-insurance, and waiting until flag leaf is equally unacceptable – in most cases," he stresses.

"However, it is acceptable for varieties with greater resistance. We tried it with Hunter and Hussar last year, and Hunter certainly did not suffer," he notes.

But arguments that early sprays protect the development of the ear and grain sites are unfounded, he maintains. "Modern, semi-dwarf varieties rarely fail to produce sufficient grain sites. We almost always have all the sink capacity we need. It is filling those sites that is the limiting factor.

Spring foliar control aims to protect the grain-filling capacity of the leaves – and that means the last three leaves. If those are treated satisfactorily an earlier spray is rarely worthwhile."


Morley demo plots

Four varieties:

&#8226 Riband – very susceptible to S tritici, but popular because farmers can control disease, like straw strength and wide market choice.

&#8226 Buster – susceptible to mildew and brown rust, but even stiffer than Riband.

&#8226 Beaufort – high treated and highest untreated yield thanks to good disease resistance.

&#8226 Brigadier – intermediate in straw strength and disease resistance.

Three input regimes:

&#8226 Untreated – no foliar fungicides.

&#8226 Targeted – sprays according to varietal disease rating, with combinations of fungicides at rates of 50% and below.

&#8226 Targeted plus pre-GS32 – early spray was 1 litre/ha chlorothalonil + flutriafol (Impact Excel) and 0.5 litre/ha fenpropidin (Patrol).