Cut costs – but safely

6 March 1998

Cut costs – but safely

Controlling cereal diseases with modern fungicides is

relatively straightforward. Doing so economically is another

matter. In this special focus we ask a leading researcher to

pinpoint the best opportunities for safe savings. We also relay

advice on the latest products, revisit the eyespot debate

and taste some research ideas. Edited by Andrew Blake

GIVEN the effectiveness of todays disease control products it is quite easy to avoid disease risks, says Neil Paveley, who leads ADASs cereal pathology research programme.

"The real trick is balancing input cost savings against risk," says Dr Paveley.

Uppermost in most growers minds are product, timing and dose. "But other aspects like variety, nitrogen use and grain value must also be remembered."

Variety choice has a big effect on the need for treatment. "But we have to be realistic. People choose varieties mainly for yield and marketability. Disease resistance comes quite low on their lists of priorities, but maybe too low. The input cost savings from disease resistance can easily be equivalent to 2-3% of yield potential and should not be ignored."

The chart shows how strongly variety influences the optimum dose (arrowed) of the fungicide tebuconazole where Septoria tritici is the main disease. "The optima all move to the right under high disease pressure and to the left under low disease pressure. But the differentials between varieties remain and apply at each spray within the programme."

Nitrogen management also affects disease and the need to spray. "It is clear that avoiding over-thick lush canopies does slow disease epidemics, especially of rusts and mildew, substantially. That reduces the need for fungicides and, therefore, costs.

"The crop canopy is effectively a three-course meal for disease. Extra nitrogen just makes it more nutritious, so the pathogen population grows more quickly."

Correct timings

Correct spray timings are vital to get the best from fungicides be they protectant or eradicant, advises Dr Paveley. "But there can be a bit of a conflict, especially with yellow rust and mildew. You cannot allow disease to get out of hand at the start of the season without having to spend a lot more later to control it.

"But the earlier we spray the less that spray contributes to yield. If you can hold off until leaf three has emerged, typically at GS32, so much the better. But there is a lot of pressure to spray at GS31 to tank mix with herbicides and/or growth regulators. The new strobilurins should give us a bit more timing flexibility, particularly if they are mixed with broad-spectrum triazoles."

Surveys suggest growers are getting the message about the importance of a flag leaf spray. "Protecting the flag leaf regardless of product is still the crucial point."

The reasoning behind this is simple, he explains. Most of the useful yield-building light falling on the crop is captured by the top three leaves. So it is largely a waste of money trying to control disease on the lower ones.

In terms of potential savings the last place to look is flag leaf emergence (GS39), he stresses. "If growers want to cut costs, reductions in ear sprays and early season treatments will be less damaging to yield than cutting back on the flag leaf spray."

One concern is that crops treated with strobilurins at GS31/32 may look so healthy at flag leaf emergence that growers may be tempted to delay the GS39 spray. "Every day they do so will lose yield," he warns.

Maximum control

When it comes to comparing products the aim must be to get maximum disease control for each £ spent, he advises. That is where guidelines on individual dose response curves, derived from three years HGCA-funded work, costing £100,000 (about 0.1% of the annual UK spend on wheat fungicides) and due to be published this spring, should help.

The initial research focused on Septoria tritici, often the number one treatment driver in the field. "The information is reliable and the main message is that the newer triazoles, like epoxiconazole, are more than worth their cost.

"We have also got similar information on yellow rust and have one years results for powdery mildew."

In most cases one disease is dominant and will steer product choice. "But we then need to think about other diseases present, how well the main product deals with them and whether there is a need to top up with something else.

"Triazoles, such as epoxiconazole, will want topping up with a morpholine where the threat from yellow rust or mildew is strong." But top-up doses need not be heavy. "For yellow rust there will be few sites where you need more than half the label dose." In most cases yellow rust control problems on Brigadier relate to poor spray timing not dose, he says.

Changes in grain price affect spray decisions but probably not as much as some growers believe, suggests Dr Paveley. A drop in price from £120/t to £80/t on average makes a difference of only 0.1 units to the optimum dose. "It is pretty small. A lower price may mean small reductions are justified. But do not use it as an excuse for cutting too much. The crucial question is where are you cutting from? If you were not spot on with selecting a dose appropriate to the risk before, you could soon run into trouble." &#42

Where can we save safely? Neil Paveley (left) outlines some fungicide options to ADAS High Mowthorpe farm manager Stephen Newell.

ADAS work shows how optimum tebuconazole dose (arrowed) varies for a range of wheats of contrasting resistance to septoria.

Optimum disease control doses for a range of wheats (in fungicide units) at different grain values (£/t)

Optimum disease control doses for a range of wheats (in fungicide units) at different grain values (£/t)

Grain price Brigadier Hunter Hussar Riband Rialto

80 0.67 0.51 0.42 0.64 0.55

100 0.74 0.57 0.48 0.70 0.62

120 0.79 0.63 0.54 0.76 0.67

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