The importance of using multi-site fungicide chemistry this spring was highlighted at a technical briefing prior to Christmas. Dominic Kilburn reports.
With a continued reduction in the effectiveness of some triazole and SDHI fungicide products, crop protection company Adama is reminding growers and agronomists to maximise the use of multi-site chemistry in their cereal disease programmes this spring.
The company says that their use is a valuable tool to manage fungicide resistance issues where key diseases such as septoria are concerned – helping to prolong the lifespan of single-site products including SDHIs, as well as providing crops with increased disease protection.
This advice is particularly timely with the imminent demise of chlorothalonil; a multi-site fungicide which has been a core component of anti-resistance strategies in cereal disease control programmes for many years. Falling foul of the EU regulatory system, chlorothalonil final use-up on farm is by 20th May 2020 and, with its use on barley as well as wheat, it’s uncertain as to whether sufficient quantities will be available this spring.
Speaking at the briefing, Adama technical specialist David Roberts said that while single-site fungicides are very effective, and there is also new chemistry available for spring 2020, in order to future-proof disease control it was critical that growers approached the season with a diverse fungicide programme. “It’s important to have started with cultural controls – such as choosing varieties with the highest disease resistant ratings where appropriate – and then add a diverse fungicide programme on top of that.
“Use of multi-site chemistry in the programme is the best way of approaching this – and stay in a protectant situation by getting application timing spot on, keeping ahead of disease,” he added.
Adama’s multi-site fungicide Arizona (folpet) is available for use on wheat and barley and comes with a maximum individual rate of 1.5-litres/ha and maximum total of 3-litres/ha on both crops.
To get the biggest effect from folpet for septoria control in wheat, and prolong the life of partner products, Mr Roberts recommends a two-spray programme (1.5-litre/ha each) at T1 and T2. “T1 is the critical timing for maximum protection although, in other seasons, when crops might be drilled earlier, then a T0 application at 1-litre/ha for early septoria is an option,” he said.
Comparing other multi-site fungicides with folpet for septoria control, including chlorothalonil and Unizeb Gold (mancozeb), Mr Roberts highlighted ADAS trials work in 2018. Here, after a two-spray programme, folpet gave additional control over mancozeb and was comparable in performance with chlorothalonil.
In 2019 NIAB trials, when used in combination with Aviator (bixafen + prothioconazole) in a two-spray treatment, Arizona delivered 12 per cent additional septoria protection compared with Aviator alone.
“A range of independent trials in the past two seasons have shown why Arizona is the ideal multi-site partner for azole/SDHI mixes including an improvement in crop green leaf area and increasing yield where septoria is the driver,” he said.
“And where we see yellow rust, folpet performs slightly better than chlorothalonil,” he added.
Resistance problems for single-site fungicides are not limited to wheat, continued Mr Roberts, who pointed out that reduced levels of activity were being seen in key diseases rhynchosporium and net blotch. However the picture for ramularia, an increasing threat across the UK, is worse. “SDHIs and azoles are struggling to control ramularia while there is complete resistance to strobilurins,” said Mr Roberts.
“There are limited options to control ramularia and so it’s very important to consider a multi-site fungicide when controlling disease in barley crops.”
Although not on its label, Mr Roberts said trials had demonstrated that the performance of Arizona against ramularia is every bit as good as chlorothalonil and to get the best effect it should be applied at T1 and T2.
“Arizona ensures crops are greener for longer, keeping ramularia off the leaves, especially when used in a split programme,” he said.
Yield increases in ramularia trials were also seen from Arizona over chlorothalonil where both products were partnered with SDHI/azoles, he added.
Multi-site and single-site – what’s the difference?
Effective control of foliar diseases such as septoria in wheat and ramularia in barley is becoming increasingly difficult to achieve due to the onset of disease resistance caused by changes in sensitivity of these pathogens to single-site fungicides. Single-site products – azoles, SDHIs and strobilurins – have one mode of action and act on individual pathways to the target fungus. Used repeatedly there is an increased risk of a fungus developing resistance.
According to Adama, multi-site fungicide folpet acts on three ‘biochemical pathways’ to the target fungus, making it difficult for fungal pathogens to become resistant and therefore the product remains unaffected by sensitivity shifts, with no field resistance to the product recorded to date.
The company says that a multi-site should be used in programmes to reduce the pressure on single-site active ingredients, to ensure robust, sustainable levels of disease control.