Management of Phoma Using Bio-and Conventional Fungicides on Fresh Market Dill

摘要

Dill (Antheum graveolens) is a popular herb frequently grown forthe fresh market. Dill and its close relative fennel (Foeniculum vulgare) are susceptible to Phoma, a foliar disease caused by the fungal pathogen Cercosporidium punctum Earle. Initial symptoms are visible in the lower canopy and may worsen under wet conditions resulting in a severely blighted plant. Older leaves first turn from green to yellow, followed by browning leaf tips. Stems lesions are frequently peppered with small black speckswhich are the fungal stromata supporting numerous conidiophores which produce spores referred to as conidia that are easily dispersed by wind and water. Rainfall, overhead irrigation, and long dew periods favor disease development. Hence there is an urgent need toevaluate candidates for control of pathogens with such potential for disease severity and the general limitations of efficacy data on herbs available. Consequently, a field experiment was conducted on dill at the Everglades Research and Education Center in Belle Glade, FL. The variety Mammoth was direct-seeded in double rows atop of six-inch raised beds formed on three-foot centers with the resident organic soil. The experiment consisted of a randomized complete block design with four replications of 12 treatments (Table I). Cercosporidium was established in the trial by distributing infected leaf material between the unsprayed dill rows serving as buffers between experimental units. Sprays were applied using a CO, backpack sprayer and a 36-inch hand-held boom equipped with three Tee-Jet 11003 flat fan nozzles angled inward for maximize coverage. Foliar sprays at a volume of 60 GPA commenced approximately five to six weeks after planting and were subsequently followed by weekly applications. Disease assessment was conducted by whole-plant visual ratings and expressed as the percentage of foliage exhibiting foliar leaf spot symptoms. The bio-rational fungicide products (biofungicides, phosphites, copper, and disinfectants) did not provide statistically significant disease control though significant reductions were achieved using the conventional fungicides. Meri von,a combination of a strobilurin and a new generation carboximide, the strobilurin Quadris, and the carboximide Fontelis performed significantly better than the other conventional fungicides. The resulting disease severities are depicted in Fig. 1. Though none of the treatments maintained disease severity below 10%, sprays were only conducted once per week and were initiated only after the onset of visual symptoms within the experiment. Of the prospects tested, both strobilurins and carboximides show promise, likely due in part to their translaminar and limited systemic activity. Growers may achieve greater efficacy with preventative sprays and, in the case of bio-rational pesticides, applications made on a much more frequent basis.