Septoria is considered the most damaging foliar disease of winter wheat in the UK, and can be responsible for up to 50% yield loss. Fungicides, azoles and the succinate de-hydrogenase inhibitors (SDHI’s) in particular, remain the most relied on form of control by growers. However, there are significant declines in the sensitivity of the septoria population to both of these fungicide groups. As legislation tightens around the availability of chemical controls with the loss of key actives like chlorothalonil, scientists are urging growers to adapt their disease management practices and utilise a combination of control methods rather than rely solely on fungicides.
It is hoped that by altering choices and practices as part of an integrated management approach, growers can save on fungicide applications whilst still maintaining long-term, effective control over septoria.
Whilst seed rate was not found to have a consistent effect on disease development, the choice of sowing date was more conclusive. As septoria infection is spread though the release of airborne spores in winter and early spring, early sowings in mid-September are exposed to spores earlier in the season when conditions are more conducive to the establishment of septoria. Therefore, sowing in mid-October significantly reduced disease severity.
To quantify this, the AHDB methodology to determine resistance ratings by variety was used to determine the difference between sowing dates. Early sowing (mid-September) was predicted to decrease the varietal septoria resistance rating by 0.6, whereas later sowing (mid-October) was predicted to increase the resistance rating by 0.6. While chemical control is available, growers are unlikely to delay drillings as later sowings are at greater risk of adverse weather conditions. However, this does enable growers to take sowing dates into account when deciding on their fungicide programme.
Furthermore, when sowing several varieties of different resistance ratings, it would be advantageous to drill the most resistant varieties first and leave the most susceptible to last, where all other agronomic factors are equal.
Variety choice and fungicide were the most critical factors, however, the effect of fungicides varied by variety. The severity of septoria was lower in varieties with greater resistance to the disease, offering growers the opportunity to reduce fungicide inputs in order to maximise margins.
The research recommends that growers should utilise all available tools using an IPM approach to maintain control of septoria. Management strategies for the control of this pathogen should start before the crop is drilled by careful selection of variety, and consideration of sowing date. Fungicide use should be the last line of defence and should take into account both the variety and sowing date. Chloe Morgan, crop pathologist at ADAS who led the project, highlights that:
"Due to the tighter legislation surrounding plant protection products and the risk of resistance development in key fungicide groups, the use of cultural control strategies is of increasing importance. Utilising more resistant varieties and taking into account sowing date will help to reduce dependence on fungicides and target them more effectively, helping to preserve new chemistry. "
The research report can be found on the AHDB website