Biology and integrated control of Pestalotiopsis on container-grown ericaceous crops

Pestalotiopsis isolates obtained from the foliage, stem-base and roots of diseased container-grown ericaceous crops (Calluna, Erica, Pieris and Rhododendron) collected from UK nurseries were identified as Pestalotiopsis sydowiana (Bresad) B Sutton on the basis of conidia morphology. Inoculum sources of the pathogen included diseased stock plants, crop debris, nursery soils, used growing media, pots and floor covering, and dust collected from greenhouse walkways. Isolates were not host-specific and infected other species of ericaceous plants, with typical symptoms including browning of foliage, stems and roots, and the presence of black or greenish black acervuli on diseased tissue. The optimum temperature for growth of three selected isolates of the pathogen was 20-25 degrees C, with little or no growth occurring below 5 or above 30 degrees C. Growth occurred over pH 2.6-8.6, with optimum at 5.5. Decreases in matric potential from -0.3 to -4.0 MPa reduced growth, which was totally inhibited at -6.5 MPa. Greenhouse trials were conducted to evaluate the effects of disease management methods (irrigation, flooring/pot disinfection and fungicide application) on control of the pathogen on potted plants of C vulgaris. Disease incidence and foliar browning caused by P sydowiana were less on fungicide-treated (five-spray programme of alternating prochloraz and carbendazim) potted plants watered by sub-irrigation compared with watering from overhead. Single and combined treatments of flooring/pot disinfection (hydrogen peroxide/peracetic acid) and the five-spray fungicide programme significantly reduced disease incidence and severity compared with dipping pots in water. The combined disinfection and fungicide programme significantly reduced disease incidence and severity, compared to disinfection or fungicide application alone. The importance of these findings for the integrated control of P sydowiana on ericaceous plant nurseries is discussed.