“It could be the worst disease year ever.”
That was the prediction ADAS plant pathologist Bill Clark gave late last month.
Septoria, mildew and rusts have all been found in crops this spring.
Or, in the case of rusts particularly, they pose a threat because of the proportion of susceptible varieties planted and the carry over of inoculum from last season.
It all adds up to it being vitally important to get the T1 spray right; allowing disease to take hold early frequently means chasing it all season.
Fortunately, growers are not short of good options.
Last season Bayer’s fungicide Proline joined epoxiconazole as an extremely effective azole fungicide, particularly against septoria, while BASF’s new offering Tracker, like Proline, adds stem-based disease control to the mix.
This season, Syngenta has launched Cherokee, a new combination of three older actives, which potentially offers a cheaper, value for money product.
And, despite the resistance issues, many agronomists believe strobilurin fungicides still have a place, albeit maybe not so much at T1.
So where should each be used?
As ever, it probably depends on the situation, which is why Farmers Weekly asked our Crop Watch agronomists to help growers target which product to choose for relatively common scenarios growers could face this spring.
Field case 1
Septoria susceptible wheat where no T0 has been applied, crop is forward and T1 looking to be applied as and when the weather permits.
Where septoria is the main driver our agronomists advise the more effective triazole-based treatments.
Proline + Bravo mix is top choice, with epoxiconazole based mixes following closely behind.
That broadly mirrors the efficacy ratings in figure 1, but suggests the agronomists perceive Proline to be more cost-effective compared with Tracker despite a similar efficacy rating.
Tim Horton’s view is typical ,suggesting Proline delivers the best yield while providing excellent persistency on septoria, even where maximum curative activity is needed.
But the feeling is if the T1 is delayed then switch to epoxiconazole-based mixes because of their better curative activity.
Alternatively, growers should increase the azole dose – how much depends on the length of the delay.
Where septoria is the main concern, strobilurins are not a great option, our agronomists suggest.
Strob use is much more likely to be worthwhile at T2.
In a high pressure septoria situation the older chemistry in Cherokee is not considered cost-effective, with agronomists believing it is not up to the job, efficacy-wise.
Whether the crop is intended for milling or feed doesn’t make much difference to agronomists at T1.
Most of them will adopt a similar strategy for both types at this stage.
Overall management strategies tend to come in at T2 and T3, Mr Horton says.
Field Case 2
Robigus, grown as a first wheat, with early foci of yellow rust detected in the field. No T0 applied
Yellow rust is anticipated to be high-risk this season, with the disease likely to develop quickly if the weather warms up.
It is an interesting scenario for growers.
Robigus is susceptible to yellow rust, and to a certain extent eyespot, but less susceptible to septoria, and that balance means a case could be made for all the options, which is reflected in the division of opinion between agronomists.
In efficacy terms, Proline’s perceived weakness to yellow rust is highlighted, while the strobilurins come back into play.
The scope to reduce rates makes them cost-effective, while growers can tailor Opus rate to septoria pressure.
Opinions are divided about what is the best option, but Tracker just pips the others, probably because of its all round ability to cover septoria, eyespot and rust.
Proline is rated the weakest, both in efficacy and cost effectiveness, but it still remains an option because Robigus can suffer from stem-based disease and septoria, particularly where early drilled and in high risk areas.
And in this situation, where the emphasis is on yellow rust, and on a cost basis, Borders-based agronomist Peter Wastling is a firm believer in Cherokee, although he warns the T2 must be applied early, as septoria cannot be ignored on Robigus.
Field Case 3
Late-drilled Istabraq after roots. No T0 applied
Late-drilled Istabraq after a root crop is a common scenario in some areas of the country.
Later drilling may well have compromised some yield potential, together with it typically being on lighter land, so most growers will definitely have a lower budget.
Although Istabraq is susceptible to septoria (rated a five) later drilling will have reduced risk, and, therefore, a popular choice will be a cost-effective triazole-based option.
Some agronomists like Cherokee in this situation, although Hants Arable System’s Steve Cook maintains reduced rates of prothioconazole are better than higher rates of older chemistry.
The strobilurin options have largely been dismissed again, but cannot be disregarded altogether, according to Agrovista’s Mark Hemmant.
He considers the physiological benefits of pyraclostrobin to be a benefit on light soils, while the boscalid in Tracker would do a similar job.
Field Case 4
Second wheat, forward crop, eyespot-susceptible variety
Eyespot management has changed since the introduction of Proline and Tracker.
Their broad-spectrum disease control means they are more justifiable at T1 than historical eyespot specific treatments.
Tracker has the edge on efficacy over Proline, according to our agronomists, but Proline is more cost-effective.
Older eyespot product Unix (cyprodinil) is perceived to be off the pace in the south.
But Mr Wastling would still consider it in a mix with Cherokee on cost grounds, and Scottish Agronomy’s Allen Scobie uses it as a mixer partner for controlling early mildew.
BASF’s Flexity (metrafenone is a good eyespot product at the higher rate, but still requires a triazole, which pushes up the cost, although it is an option where mildew is a problem.
Field Case 5
Early drilled wheat with high take-all risk.
It is arguably a bad management decision to drill early when take-all risk is high, but where the risk is high a strobilurin is likely to be used.
Amistar is the top choice.
Although it’s efficacy is not rated particularly highly, it is better than any of our other options.
Our agronomists also expected that other stem-based diseases would be a probable issue in this situation, so Tracker and Proline followed in our rankings.
An alternative choice is Fandango (fluoxastrobin + prothioconazole), which fits a take-all plus stem-based disease scenario, although some agronomists favoured switching the Opus in the Amistar mix to Proline to deliver the same result.