Foliar Nematode Control Using New Nematicide Formulations and Ornamental Plant Safety Associated with Several New Nematicides

Abstract

Aphelenchoides fragariae is a species of foliar nematode that is an increasingly widespread pathogen of ornamental crops with a wide host range, attacking more than 250 plants species in 47 plant families. The most recognizable field symptom of foliar nematodes is the interveinal lesions on leaves. Previously, chemical treatments using active ingredients such as methyl bromide, oxamyl and parathion were effective against foliar nematodes. However, due to environmental concerns and their high toxicity, these chemicals are no longer available for foliar nematode control. The overall goal of this study is therefore to determine the effectiveness of several new, reduced-risk nematicides against foliar nematodes on certain popular ornamental plants in Hawaiʻi. Specific objectives are 1) the efficacy of several newly developed nematicides for managing foliar nematodes on the fern species Microlepia strigosa; and 2) if these newly developed nematicides have phytotoxicity effects on ornamental plants commonly used in Hawaiʻi's landscape industry; Microlepia strigosa, Frangipani, Raphiolepsis indica, Hibiscus, Phalaenopsis, and Anthurium adreanum. Foliar nematodes were extracted from infected fern tissues using the Baermann funnel technique. These nematodes were cultured in the lab using carrot discs and the cultures were refreshed every 5-7 weeks. New nematicides ESP 715 consisting of fluopyram as the active ingredient (a.i.) along with two other bionematicides, MBI 304 and Majestene, with a.i. of Chromobacterium spp. strain extract and Burkholderia spp. strain extract, respectively, were tested for potential control of Aphelenchoides spp. on Microlepia strigosa. Height, width and weight of fern were assessed weekly over 6 weeks after foliar nematode inoculation on the leaves. Foliar nematode damage was assessed at the end of the experiment. In addition, ESP 715, MBI 304 and Majestene were examined for phytotoxicity on M. strigosa, Frangipani, R. indica, Hibiscus, Phalaenopsis, and A. adreanum at various rates: Fluopyram at 0 ml/L, 0.33 ml/L, 0.66 ml/L and 1.34 ml/L. Except palapalai which was only tested with 2 rates of fluopyram: 0.66ml/L and 1.34 ml/L. Additionally MBI 304 and Majestene were examined for phytotoxiticy on M. strigosa plants: MBI 304 at 4,793 mg/L and MBI 205 at 20 ml/L. All plants treated with these nematicides received three applications at 14-day intervals. Untreated plants were included as the control. No visual foliar phytotoxicity symptoms were observed on all treatments throughout the 26-week evaluation period for Frangipani, R. indica, Hibiscus, Phalaenopsis, and A. adraeanum and the 14-week period for bionematicides on M. strigosa., except for fluopyram on M. strigosa. Fluopyram at both tested rates caused visual phytotoxicity effects. 0.66 ml/L of fluopyram caused severity ratings of 1.05 on the 0-5 scale. 1.34 ml/L of fluopyram caused severity ratings of 0.95. Severity ratings for both rates of fluopyram were significantly higher than the noninoculated control and significantly lower than the inoculated control. However, fluopyram did not suppress foliar nematodes. Burkholderia and Chromobacterium did not suppress the number of foliar nematodes significantly but reduced the numbers by 65.7% and 75.8%, respectively. Although various plant growth factors were stunted on hibiscus, orchid, anthurium, indian hawthorn and plumeria by fluopyram, it did not affect the marketability of the plants as no visual foliar phytotoxicity symptom was observed.