Fungicide rate cuts can be a false economy
By Robert Harris
LOW-DOSE fungicide programmes are a false economy, especially when using the latest chemistry.
That was the blunt message national disease experts had at a recent briefing organised by agrochemicals supplier BASF.
In low disease years such strategies can control disease as effectively as more robust regimes. But hidden yield losses make such programmes less cost effective, according to industry opinion.
Although average UK yields are rising at about 1.5% a year, yields have levelled out on many of the best farms. ADASs national cereal pathologist Bill Clark believes the increasingly popular low-dose approach based on disease levels alone is mainly to blame.
"We were getting 10t/ha in fungicide trials a few years ago. Now we are getting 11.5-12. That increase has not been reflected in farm performance."
Work at ADAS Rosemaund in the past two seasons showed the economic optimum application of tebuconazole (Folicur) was 1.5 litres/ha (1pt/acre) on Riband despite low septoria pressure. "That is a lot of fungicide – most farmers would not have applied anything like that."
Further work with epoxiconazole (Opus) on Brigadier-type varieties in 1995 showed little difference in disease control between full- and half-rate applications when chemical was applied at the right time. But yields fell by up to 0.5t/ha (0.2t/acre) at the lower rate.
"Simple disease levels dont give the whole answer. There are hidden yield benefits which are not taken into account," says Mr Clark. Maintaining the size and greenness of the canopy is one probable reason, he believes.
Another reason is that higher rates stimulate the plants own resistance mechanisms, says Joseph Appel, BASFs head of western European fungicide development.
He has also found that full rates more than cover the extra cost. Company trials in France in 1995 showed with two half-rate sprays, yields were 0.35t/ha (0.14t/acre) less than with two full-rate ones, worth over £39/ha (£16/acre).
Unaware how much
Farmers are unaware of how much yield they are losing, says Mr Clark. They tend to assess a consultants worth by how much he saves them, rather than how much extra yield they produce.
"Cost savings are easy to measure and provided they continue to get 8.5-9t/ha crops they are happy. But if you cut rates by a quarter and you lose 1% of yield, that is losing money.
• Further support for full-rate fungicides appears on page 52.
• Better disease control.
• Prolongs life of green tissue
to give more yield.
• Better curative and protectant activity.
• Fewer passes needed.
• Timing less critical.
• Less resistance risk.
• Higher yields and profits.