Oilseed rape crops should be treated more like wheat when it comes to the spray timing at flowering, believes Zantra’s technical director Chris Bean.
That’s because the threat from sclerotinia is only one reason for making an application at this key timing, he explains, adding that it should be given the same emphasis as the T2 spray in cereals.
“Even in the absence of the disease, there will be a response from an early petal fall or mid-flowering spray,” he points out.
“Preserving green leaf and pod area is important. It drives up yields by maintaining photosynthetic area and makes a big difference to the final results,” Mr Bean adds.
Late infections of phoma and light leaf spot, as well as alternaria, botrytis and – in some areas – powdery mildew, may all need controlling.
Sclerotinia threat in 2014
Wet weather during flowering is the most important factor in determining whether sclerotinia will be a problem, although heavy dews after a dry flowering period can also trigger a spore release.
“If we get wet weather at flowering, the risk increases. Growers will know if their fields have a history of the disease, as it overwinters in the soil,” Mr Bean says.
Sclerotinia control doesn’t only come from flowering sprays, as a good dose of triazole at the green to yellow bud stage can produce a substantial reduction in the disease, he says.
Mr Bean suggests the first flowering spray should be applied at early to 20% petal fall, which will give protection for two to three weeks, so if flowering continues, or the weather becomes wet, then another treatment may be needed.
Late flowering varieties, such as Cabernet, can be susceptible to April frosts, which remove the first flush of flowers.
“Varieties like this then flower again, so the risk can return. That’s why a large proportion of the crop gets sprayed twice,” he says.
“There’s more than one reason for going through the crop at this stage. Doing nothing really isn’t an option,” he adds.
Last year’s low disease levels meant the new SDHI plus prothioconazole fungicide mixes weren’t given much of a test, with little response seen with products such as Recital and Propulse, or Skyway and Sparticus.
“Based on current knowledge and experience, these mixes seem to add to the disease control options, rather than being obvious replacements for the existing products,” Mr Bean says.
An older straight SDHI product Filan (boscalid) has always been a significant product at the flowering spray timing, especially where the sclerotinia risk is high, although it is often in short supply, notes Mr Bean.
“Alternatives are to use a lower rate of Filan with a triazole, or just a triazole, or azoxystrobin plus some triazole. In lower risk crops, mixes with thiophanate methyl, as in Taurus, are also viable options,” he says.
Propulse (ProCam) and Recital (Agrovista): SDHI fluopyram + triazole prothioconazole
Skyway (Frontier) and Sparticus (Hutchinsons): SDHI bixafen + triazoles prothioconazole + tebuconazole)
Filan; SDHI boscalid
All of these options work well on sclerotinia, although there are differences when it comes to other diseases.
“Filan on its own, for example, is not very good on alternaria, but in mixture with a triazole, it gets a boost and offers very similar activity to the newer products on late season diseases,” Mr Bean adds.
While there is some new chemistry around, the activity and attributes of some of the older products, including triazoles, shouldn’t be forgotten.
“They tend to give better, longer alternaria control and provide the best hope against powdery mildew. Mixes based on prothioconazole or prochloraz give good control of light leaf spot and phoma,” he adds.
Just as the triazoles improve results from the SDHIs, they also add significantly to the activity of azoxystrobin.
“Azoxystrobin contributes to both disease control and green leaf area retention, and is one of the few materials to give any control of Verticillium wilt,” he says.
Mixing fungicides with partners with different modes of action is very important. “There are just the same risks of resistance developing as there are in cereals,” he says.