Yield and disease control in winter wheat in southern Sweden during 1977–2005

Fungicides are routinely used to prevent yield losses in winter wheat in southern Sweden. Yield and 1000 grain weight (TGW) data from 432 trials in farmers' fields were evaluated to review long-term yields (1977–2005) and control of eyespot and Leaf Blotch Diseases (LBDs, including Septoria tritici blotch, Stagonospora nodorum blotch and tan spot), powdery mildew, brown rust and yellow rust. Regression analyses revealed that control of LBDs explained 74% of the yield increase achieved by fungicide treatment at GS 45–61, followed by powdery mildew (20%), brown rust (5%) and yellow rust (1%). Yield of both untreated and fungicide-treated plots increased from approx. 6000 to 12 000 kg ha−1 over the period 1983–2005. Single eyespot treatment improved yield by ∼320 kg ha−1 yr−1 during the period 1977–2002, mainly due to occasional years with severe eyespot. Single leaf disease treatment at GS 45–61 increased mean yield by 10.3% or 810 kg ha−1 yr−1 (9.9% or 660 kg ha−1 yr−1 for 1983–1994 and 10.7% or 970 kg ha−1 yr−1 for 1995–2005) due to increased TGW and grain numbers, especially in high-yielding stands. Additional extra early treatment at GS 30–40 against LBDs increased yield by ∼250 kg ha−1 yr−1. Estimated variance in yield and TGW was higher between years than within years, while that in yield increase and plant diseases was lower between years than within. The results confirm potential and limits of fungicides and the need for supervised control strategies including factors affecting disease, yield and interactions.