With growers more concerned on checkinglush, forward OSR theres a danger that autumn disease control could becompromised this season.
The popular PGR choices are not the mosteffective for phoma and lightleaf 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 itcomes to disease control.
Adding to the problem is higher than usualsoil temperatures, limiting the ability of growers to apply the herbicide KerbFlo 500 (propyzamide). The hope of many growers is to hold off and mix with afungicide but Dr Peter Gladders of ADAS says time is running out. Where cropswere racing away it was the right decision to apply PGRs last month but thedanger is that these products are rapidly running out of steam, or have done soalready. Even some average sized plants are showing infection levels of 50 percent so I dont think there is any other option than getting on now with aneffective Phoma product. Thedisease can cost you 0.5t/ha in lost yield, he points out.
Bayers Tim Nicholson also says diseasecontrol should be the priority. I can understand growers wanting to reduce apass by mixing Kerb and fungicide but I think delaying effective phoma and LLS applications is a risk.
Phomalevels can increase rapidly once plants are infected, and early control of LLSis a must as eradication isnt really an option. Fungicides with PGR activitysuch as tebuconazole and metconazole arent robust enough for dual activityagainst phoma and LLS, and manycrops could be left exposed without an effective dose of prothioconazole, hesays.
Where a suitable first phoma treatment wasnt applied andconsidering the upcoming LLS threat, his advice is to treat with a robust doseof an effective phoma + LLSproduct such as 0.46l/ha dose of Proline275, and monitor things fromthere. Keep a close eye on crops, especially the more susceptible cultivarsand those close to debris from previous crops, he warns.
And Dr Gladders is also cautioning againstcomplacency with LLS. Despite the latest Rothamsted forecast downgrading therisk, he suggests that infection levels could be similar to last spring. Therisk is calculated on pod incidence data and deviation from 30 year mean summertemperature and rainfall data. However, it doesnt include stem infectionlevels which remained high and so I expect light leaf spot to be a significantfactor this season. Growers might not appreciate the need for a robustapproach.
His advice is to get in now and look againearly in the New Year. We saw the damage the disease can do last season in thesouth so autumn applications must factor in LLS control too. You simply cannotafford to let the disease in and its cycle can be as short as six weeks, evenin cold conditions. Therefore I would urge growers to back up autumn sprayswith a follow up treatment at the earliest opportunity in the New Year, heconcludes.