T3 sprays targeted at fusarium species on wheat, where azoles are the key active ingredient, are associated with the selection of fungicide insensitive septoria strains.
As part of a resistance management strategy, ear sprays should be considered carefully and tailored to field-by-field risks, according to AHDB.
Weekly fusarium infection risk forecasts, published by AHDB during the main flowering period, can be used alongside local knowledge to guide the T3 spray decision.
Fungicide resistance guidance for cereals has also been updated and issued by the Fungicide Resistance Action Group UK (FRAG-UK).
AHDB monitoring has tracked a continual decline in the efficacy of azoles against septoria since the mid-90s. Azole insensitivity appears to be driven by application number and less so by dose, according to FRAG-UK.
At the 2016 AHDB Agronomists’ Conference, ADAS’ Neil Paveley stated that the use of three or four azoles per year would ‘drive efficacy against septoria into the ground’.
Because of the importance of T1 and T2 sprays, he stated that the T3 timing provided one of the few opportunities to consider missing an azole application.
He said: “If a crop has good resistance to septoria, the T2 doesn’t need topping up because it is dry and fusarium infection risk is low, then agronomists need to consider the benefits and risks from a T3”.
He added: “If we spray every crop four times to minimise all disease risks for the current season, we risk running out of effective chemistry over the longer term.”
Fiona Burnett, chair of FRAG-UK, commented: “Fusarium infection risk is driven by rainfall at flowering and ripening, so many crops merit protection.
“Many growers do need to manage septoria at T3, particularly in susceptible varieties on heavy land and in the North, where late green leaf area retention is particularly important to yield.
“To protect future efficacy, therefore, T3 sprays must be tailored to the twin risks of fusarium and septoria on a field-by-field basis, with products, doses and mixture partners selected accordingly.
“Accurate T3 timing is key to avoid the need for any additional late top-up sprays. T4 sprays should be avoided as they add massively to resistance risk and, as fungicide efficacy against fusarium drops rapidly once infection is established, there is little evidence of them being helpful to yield and quality.”
Fusarium infection risk forecasts have been published on cereals.ahdb.org.uk/monitoring throughout the main flowering period since 2014. The weekly forecasts can be used to assist with the planning of T3 sprays and the completion of the mycotoxin risk assessment.
Based on crop growth stage information, gathered by an established network of independent agronomists covering 30 counties in England and Scotland, and daily rainfall data, the forecasts provide an early indication of both national and regional fusarium infection risk.
The forecasts will also include spore-level information from a network of air samplers. The network has been used to inform AHDB’s sclerotinia infection risk forecasts over the last few seasons and the approach will be extended to fusarium for the first time this year.
If a T3 spray is judged to be necessary, then AHDB fungicide activity and performance information can be used to guide product choice, as the performance of azoles against fusarium head blight and levels of fusarium mycotoxin deoxynivalenol (DON) are now assessed in trials. Trials highlight that not all azoles are effective equally against both septoria and fusarium.
There are no reports of resistance to azoles in species which cause fusarium head blight, according to FRAG-UK. Where azoles are used, however, they should be protected by the addition of a multisite. Strobilurins have no activity and SDHIs do not offer strong control and are, therefore, best limited to T1 and/or T2 timings to protect their efficacy.