Management of Stemphylium leaf spot (Stemphylium vesicarium) and rust (Puccinia asparagi) of asparagus (Asparagus officinalis) with cultivar selection and fungicides

Stemphylium leaf spot (SLS) and rust are foliar diseases of asparagus fern. If left unmanaged, both SLS and rust can contribute to early decline of an asparagus field and a reduction in yield in subsequent seasons. Currently, growers rely on protectant foliar fungicides and cultivar selection to control foliar disease in asparagus in Canada. However, it is unclear which new cultivars are less susceptible to foliar disease and if any new fungicides might provide adequate control. The objectives of this research were to: (1) assess cultivars and experimental breeding lines for sensitivity to foliar disease, and (2) evaluate fungicides for control of foliar disease in asparagus. A cultivar trial was established in 2011 to compare six cultivars and lines. Also in 2011, thirteen fungicides and combinations of fungicides were assessed for control of foliar disease in ‘Guelph Millennium’. In both studies, the fern was assessed for symptoms of SLS and rust. ‘Jersey Giant’ and ‘Guelph Equinox’ and lines UG010 and UG023 had lower rust severity (as measured as standardized area under the disease progress curve, sAUDPC) than ‘Guelph Millennium’ and ‘Tiessen’. ‘Jersey Giant’ also had lower SLS disease severity index (DSI) and sAUDPC than ‘Guelph Millennium’ and ‘Guelph Equinox’ and the line UG023. There was a negative correlation between SLS and rust for both sAUDPC and DSI assessments. In the fungicide screening trials, differences were observed in lesion counts and sAUDPC. In a 3-year-old field, azoxystrobin/cyproconazole, azoxystrobin/difenoconazole, benzovindiflupyr, cyproconazole, tebuconazole, and the tank-mixture of mineral oil + pigment + propiconazole had lower sAUDPC than the untreated control. In the 4-year-old field, only azoxystrobin/cyproconazole, azoxystrobin/difenoconazole, and cyproconazole had lower sAUDPC than the untreated control. Further research is warranted to investigate rust management programs with fungicides on slow-rusting asparagus cultivars.