How to control yellow rust in wheat without epoxiconazole
© Blackthorn Arable Epoxiconazole was once the mainstay active for cost-effective yellow rust control in winter wheat, but despite its withdrawal, a number of options remain available for use this spring.
After the EU ban of epoxiconazole in April 2020, the Chemicals Regulation Division prohibited the use or storage of products containing the active in the UK from 31 October 2021.
This now leaves growers reliant on remaining azole chemistry, which often comes with a more hefty price tag than epoxiconazole. Strobilurins and SDHIs can also provide control.
See also: Two new fungicides to fight septoria in wheat grower’s plans
Perhaps preventing the over-application of the most obvious replacement, tebuconazole, will be a key aim, particularly now as question marks loom over the active’s future.
Actives
- Revystar (fluxapyroxad + mefentrifluconazole)
- Univoq (fenpicoxamid + prothioconazole)
- Elatus Era (benzovindiflupyr + prothioconazole)
- Ascra Xpro (bixafen + fluopyram + prothioconazole)
As remaining chemistry suppresses rather than cures the disease, controlling yellow rust early in the programme will be more important than ever.
Below, we speak to two agronomists from across the country to get tips on how farmers can keep on top of the disease.
Jock Willmott, partner and agronomist, Ceres Rural
© Ceres Rural
Ceres Rural’s Jock Willmott says that tebuconazole will most likely “hold the fort” and act as the main fungicide replacement in the absence of the cost-effective active epoxiconazole.
“Tebuconazole can provide effective control to clean up and protect crops at the T0 timing where rust is identified in a crop and a known history of the disease is apparent,” says Mr Willmott.
However, he warns growers to be mindful of product labels as they can be quite different on total maximum dose and intervals between application.
What’s more, he talks of potential concerns over the future of tebuconazole as its extension of use is up for renewal in just two years.
Other effective options include strobilurins such as pyraclostrobin and azoxystrobin, which provide effective yellow rust control when used at T0 and T1.
“In fact, these actives offer greater persistency compared with available azole chemistry.”
It is worth noting strobilurins can only be used a maximum of two times within a programme, so an azoxystrobin/tebuconazole mix could benefit.
Further azole actives to consider include prothioconazole, but this is considerably more expensive than epoxiconazole, costing about £43/litre rather than the previous £15/litre.
While prothioconazole fills the septoria gap, it is less effective on yellow and brown rust than epoxiconazole. A prothioconazole/tebuconazole co-formulation could be used instead.
“There’s also metconazole, but again this is a good deal more expensive than tebuconazole costing about £15/litre, which growers would most likely reach for first.”
Yellow rust usually occurs earlier on in the season at sub-16C, therefore it’s main spray control timings are T0 and T1.
From T2 onwards, yellow rust pressure begins to decrease, and depending on location, brown rust will begin to take hold, mostly in the East.
At this timing, SDHIs and some of the new materials such as Revystar and Univoq can be used, but Mr Willmott reports these are not as effective at controlling rust as epoxiconzole once was.
“The SDHI Solatenol can also be used, it is a great rust product but is generally only found in more expensive mixes,” he says.
Mr Willmott highlights the major drawbacks of losing epoxiconazole as remaining alternatives mostly hold and protect from yellow rust, unlike epoxiconazole, which eradicated and protected the crop from disease.
“Although epoxiconazole wasn’t the quickest-acting chemical, it was good at protecting the crop against disease and proved very effective when used within a mix,” he adds.
He also notes that modern wheat varieties are more susceptible to yellow rust at younger growth stages. This susceptibility is relative to growth, so as crops develop, they gain resistance.
“In a slower growing year, crops will, therefore, reach this resistance stage later and remain vulnerable to yellow rust for a longer period of time.”
If rust settles in a crop early on in the season, growers should remain vigilant as fungal spores are most likely to disperse through the crop, keeping disease pressure persistent throughout the season.
“With this in mind, growers should ensure even spray coverage throughout the crop. If a field section around a tree or headland is missed, this can harbour disease, allowing rust levels to build up and spread within the crop,” he concludes.
David Boulton, independent agronomist, Indigro
© Indigro
Epoxiconazole was once the mainstay for yellow rust control, where a low-rate application of Cortez at T0 or SDHI mixture such as Adexar at T1 would stop yellow rust in its tracks, explains David Boulton, independent agronomist at Indigro.
As yellow rust tends to manifest itself early in the season in March and April, when temperatures are warming, its key control timings are T0 (GS30) and T1 (when leaf three has emerged).
“A 50% dose of tebuconazole combined with a 30-40% dose of azoxystrobin or a 30% dose of the strobilurin pyraclostrobin can provide effective protection and curativity against overwintered yellow rust at the T0 timing,” explains Mr Boulton.
For a robust T1 option, he recommends the SDHI Solatenol (as contained in Elatus Era), or for low-risk scenarios, he lists a number of potential options:
- Revystar
- Ascra Xpro
- Univoq
Mr Boulton highlights the importance of growing varieties with good disease resistance, and for growers to be mindful of variety parentage – particularly now as a greater number of races and strains of yellow rust have emerged and overcome breeding resistance.
“Some varieties with high resistance ratings can show symptoms of yellow rust during winter and early spring because they are susceptible at the early stages of development [seedling stage].”
In this scenario, a curative fungicide may be required at T0 to prevent the further development of the disease, and the variety should grow away from the yellow rust pressure, showing its true adult plant resistance.
Highly resistant and stable varieties, such as Crusoe and Siskin, will generally not require yellow rust control at T0, whereas Skyfall and Zyatt will most likely require fungicide control at both T0 and T1 timings, he concludes.
