MANAGEMENT OF PHYTOPHTHORA ROT ON UK ASPARAGUS CROPS

Prior to 2002, reports of Phytophthora rot on asparagus (Asparagus officinalis) in the UK were rare. The disease has subsequently been reported and confirmed each season, causing concern to the industry because of serious yield losses (>50 %) attributed to the disease in New Zealand and California. Due to the potential impact of the disease on the UK industry, pre-harvest use of the fungicide SL567A (480 g/L metalaxyl-M) was approved in spring 2004 and a research project instigated to further investigate the epidemiology and control of the disease. In 2004, Phytophthora on asparagus was confirmed on farms in five different regions of the UK. Analysis of the rDNA ITS sequence at SCRI confirmed that the disease was caused by the same species found in New Zealand and France (to be described as Phytophthora asparagi). A DNA-based molecular diagnostic test was developed and successfully applied to plant material. In an inoculated field trial (Norfolk, UK), there were significant effects of SL567A on crop establishment, with a soil application immediately post-planting (0.65 L/ha) resulting in higher plant counts, plant vigor and fern height than the inoculated control treatment. In a mature crop with natural Phytophthora infestation (Cambridgeshire, UK), a pre-harvest application of SL567A (1.3 L/ha) delayed symptom development until the fifth week of harvest compared to untreated control plots, where spear rot was observed in the second week of harvest. Implications of the disease for the UK asparagus industry will be discussed.