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The popular PGR choices are not the most effective for Phoma and Light Leaf Spot (LLS) control, especially when disease is already established. With Phoma thresholds now being exceeded, and a key LLS timing approaching, growers should not be complacent when it comes to disease control.

Adding to the problem is higher than usual soil temperatures, limiting the ability of growers to apply the herbicide Kerb Flo 500 (propyzamide). The hope of many growers is to hold off and mix with a fungicide but Dr Peter Gladders of ADAS says time is running out. “Where crops were racing away it was the right decision to apply PGRs last month but the danger is that these products are rapidly running out of steam, or have done so already. Even some average sized plants are showing infection levels of 50% so I don’t think there is any other option than getting on now with an effective Phoma product. The disease can cost you 0.5t/ha in lost yield,” he points out.

Bayer’s Tim Nicholson also says disease control should be the priority. “I can understand growers wanting to reduce a pass by mixing Kerb and fungicide but I think delaying effective Phoma and LLS applications is a risk.

“Phoma levels can increase rapidly once plants are infected, and early control of LLS is a must as eradication isn’t really an option. Fungicides with PGR activity such as tebuconazole and metconazole aren’t robust enough for dual activity against Phoma and LLS, and many crops could be left exposed without an effective dose of prothioconazole,” he says.

Where a suitable first Phoma treatment wasn’t applied and considering the upcoming LLS threat, his advice is to treat with a robust dose of an effective Phoma + LLS product such as 0.46l/ha dose of Proline²⁷⁵, and monitor things from there. “Keep a close eye on crops, especially the more susceptible cultivars and those close to debris from previous crops,” he warns.

And Dr Gladders is also cautioning against complacency with LLS. Despite the latest Rothamsted forecast downgrading the risk, he suggests that infection levels could be similar to last spring. “The risk is calculated on pod incidence data and deviation from 30 year mean summer temperature and rainfall data. However, it doesn’t include stem infection levels which remained high and so I expect light leaf spot to be a significant factor this season. Growers might not appreciate the need for a robust approach.”

His advice is to get in now and look again early in the New Year. “We saw the damage the disease can do last season in the south so autumn applications must factor in LLS control too. You simply cannot afford to let the disease in and its cycle can be as short as six weeks, even in cold conditions. Therefore I would urge growers to back up autumn sprays with a follow up treatment at the earliest opportunity in the New Year,” he concludes.