Comparative Performance of Reduced-risk Fungicides and Biorational Products in Management of Postharvest Botrytis Blight on Bigleaf Hydrangea Cut Flowers

Abstract

Botrytis cinerea is one of the problematic and notorious postharvest pathogens of bigleaf hydrangea (Hydrangea macrophylla) cut flowers. It causes flower blight, leaf blight, and stem rot, reducing the ornamental value (such as longevity, color, and texture) of flowers, ultimately making them unsalable. The objective of this study was to identify effective conventional fungicides and biorational products for botrytis blight management on bigleaf hydrangea cut flowers that can be easily and readily adopted by growers of ornamentals. Preventive preharvest whole-plant spray and postharvest dip treatment applications were used in this study. For the whole-plant spray applications, bigleaf hydrangea plants were sprayed with treatment solution 3 days before harvesting flowers. For the dip applications, cut flowers were dipped in treatment solutions after harvest. For both application types, flowers were inoculated with B. cinerea spores once treatment solutions dried. Flowers were stored in cold storage for 3 days and then displayed in conditions similar to retail stores. Botrytis blight disease severity, marketability of flower (postharvest vase life), phytotoxicity, and application residue were assessed in the study. Treatments showed variable efficacy in managing postharvest B. cinerea infection in bigleaf hydrangea cut flowers. Preventive preharvest whole-plant spray and postharvest dip applications of isofetamid and fluxapyroxad + pyraclostrobin significantly reduced the postharvest botrytis blight disease severity and area under disease progress curve (AUDPC) compared with the positive control (nontreated, inoculated with B. cinerea). When applied as a postharvest dip, the fungicide fludioxonil and biofungicide Aureobasidium pullulans strains DSM 14940 and DSM 14941 effectively lowered the disease severity and disease progress (AUDPC). These effective treatments also maintained a significantly longer postharvest vase life of bigleaf hydrangea cut flowers compared with the nontreated, inoculated control. The longer vase life may be attributed to lowered botrytis blight disease severity and the resultant proper physiological functioning of flowers.

Powdery Mildew of Bigleaf Hydrangea: Biology, Control, and Breeding Strategies for Resistance

“…Biorational products can be adopted for fungal disease management. These products refer to pesticides of natural origin such as botanicals, minerals, microorganisms, and minimum-risk chemicals that have reduced or no negative effects on the environment or beneficial organisms [49,50]. Biocontrol of powdery mildew was achieved on various hosts, including Trichoderma isolates [23,51], yeasts, mycophagous arthropods, mycolytic bacteria, and additional effective biological agents.…”

“…It is also suggested that root symbiosis with rhizobia can be used by priming plants with salicylic acid accumulation and defense-gene expression, which is triggered by powdery mildew [23]. However, the downside to certain biological control and biorational products is the limitation of efficacy in wider field conditions [50]. There is also the concern of non-native species posing an ecological risk [47].…”

“…Similarly, fertilization and irrigation need to be tailored to the specific species. Too little fertilization can result in nutrient deficiencies and too much can result in excessive growth of new shoots, which could be more susceptible to plant pathogens [24,37,50]. The host plant growth rate increases with the level of nitrogen available.…”

“…Pruning infected or overcrowded plant material can help to remove the disease and increase air circulation [57]. Disinfecting and sterilizing surfaces and equipment, such as pruners, is key to limiting potential spread of inoculum [50]. However, cultural control methods require both knowledge of crop and pest biology and how they interact.…”