Optimal strob use cuts production costs
GROWERS must abandon fixed ideas on fungicide budgets, delegates at last weeks Arable Research Institute Association meeting at IACR Long Ashton heard.
"Some still have an upper limit for fungicide spend in their head," said ADAS Boxworths Bill Clark. "These are the farmers that are going out of business."
Focusing on unit cost of production is the approach that must be adopted, especially for modern fungicides such as the strobilurins, he stressed. "Growers should ask are they cost effective, not can I afford to use them."
But greater technical knowledge is required with todays application decisions and common sense could not be relied upon. Consultant advice was increasingly important and consultants should be armed with effective computer support, he maintained.
"Decision support is becoming essential even for consultants. The chap who stands in the field and recommends a 0.6 litre/ha rate is making a guess. He cannot carry the dose response curves to over 200 products in his head."
Misconceptions among growers, such as thin crops needing less fungicide, were leading to less than optimal use of strobilurins on farm, he said. "The last thing you should do with a thin crop is cut back, especially at T1. Canopy size may be critical, so any loss of green leaf area could be very important," he warned (see table).
Such misconceptions stem from the common sense approach adopted with triazoles. Once disease is controlled, yield response curves plateau. But with strobilurins, dose responses are achieved even in the absence of disease.
ADAS work shows that a double dose of Amistar (azoxystrobin) can add 1t/ha over a single dose. An economic response, even if illegal, he pointed out.
"This is a phenomenon of the strobilurins, which is not related to disease control," he concluded. *
• Forget budgets for fungicides.
• Concentrate on cost per tonne.
• Decision making more complex.
• Common-sense approach leading to mistakes.
Contribution to yield
Leaf Thin crop Thick crop
Ear 24% 24%
Leaf 1 33% 47%
Leaf 2 30% 20%
Leaf 3 12% 8%
Leaf 4 1% 1%