Identification of alternatives for the management of foliar nematodes in floriculture

The foliar nematodes, Aphelenchoides spp, have emerged as important pests of ornamentals in North America during the last decade. Due to the ban on the use of potentially toxic pesticides, there are currently no nematicides registered to manage foliar nematodes on ornamentals. Therefore, we have evaluated a biological [Burkholderia cepacia (syn Pseudomonas cepacia)], two plant products [clove (Syzygium aromaticum) extract and Nimbecidine (azadirachtin)] and twelve chemical pesticides registered for the management of insects, mites, slugs or diseases of ornamentals, against Aphelenchoides fragariae on the most popular ornamental, hosta (Hosta spp), for two consecutive years. We found ZeroTol (270 g liter-1 peroxyacetic acid), currently labeled as a broad-spectrum fungicide/algicide, to be a very potent nematicide that killed 100% of the nematodes in water suspension. It also caused over 70% reduction in A fragariae population in soil and in the leaves without any phytotoxicity. B cepacia caused 67-85% reduction in A fragariae population in leaves and 50% reduction in the soil whereas insecticidal soap caused over 72% reduction in leaves and 61% reduction in the soil. Clove extract and Nimbecidine did not show any potential for the control of A fragariae on hosta. Although all twelve chemical pesticides were effective in reducing the population of A fragariae in the soil 45 days after treatment (DAT), only diazinon 475 g liter-1 EC, trichlorfon 800 g kg-1 SP, ethoprophos 100 g kg-1 GR, oxamyl 100 g kg-1 GR and ZeroTol caused over 70% reduction in nematode population compared with the control. In the leaves, only diazinon EC, trichlorfon SP, insecticidal soap, oxamyl GR and ZeroTol consistently caused over 70% nematode population reduction compared with the control at 45 DAT in both years. Thus, only diazinon EC, trichlorfon SP, oxamyl GR and ZeroTol consistently caused over 70% reduction in nematode population both in soil and leaves. Due to the recent ban by the US Environmental Protection Agency on the use of the first three of these formulations, only ZeroTol would serve as an effective tool to manage foliar nematodes in ornamentals. Although not as effective as ZeroTol in the soil, insecticidal soap is the only other alternative for foliar nematode management.