Effects of fluopyram and azadirachtin integration with sunn hemp on nematode communities in zucchini, tomato and sweet potato in Hawaii

Authors: WAISEN, PHILIP - University Of Hawaii; WANG, KOON-HUI - University Of Hawaii; UYEDA, JENSEN - University Of Hawaii; Myers, Roxana

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2021
Publication Date: 3/6/2021
Citation: Waisen, P., Wang, K., Uyeda, J., Myers, R.Y. 2021. Effects of fluopyram and azadirachtin integration with sunn hemp on nematode communities in zucchini, tomato and sweet potato in Hawaii. Journal of Nematology. 53:1-15. https://doi.org/10.21307/jofnem-2021-030.
DOI: https://doi.org/10.21307/jofnem-2021-030

Interpretive Summary: Plant-parasitic nematodes are detrimental pests that adversely affect plant health and yields in fruit and vegetable crops. Of particular importance are root-knot and reniform nematodes which cause severe damage to the root system. Fluopyram and azadirachtin have both shown promise to manage plant-parasitic nematode infestations in several agriculturally important crops. In this study, three field trials were conducted to test the efficacy of these nematicides on zucchini, tomato, and sweet potato. Early applications of fluopyram were successful at reducing root-knot nematode populations in all fields. When combined with a sunn hemp cover crop, fluopyram suppressed reniform nematode in the short-term zucchini crop only. An application of azadirachtin in combination with pre-planting sunn hemp reduced reniform nematodes but was not effective against root-knot nematode. Crop yields were highest with fluopyram and azadirachtin treatments when combined with pre-plant sunn hemp. In addition, the incorporation of a sunn hemp cover crop reduced the negative impacts of the nematicides to the beneficial free-living nematode communities.

Technical Abstract: Fluopyram (Velum® One) is a synthetic nematicide and azadirachtin (Molt-X®) is a biological nematicide. Both have shown promise against plant-parasitic nematodes on several agriculturally important crops. There is a lack of information on integration of pre-plant sunn hemp (Crotalaria juncea) cover crop with these post-plant nematicides, aiming to improve plant-parasitic nematodes management and mitigate any detrimental effects on free-living nematodes. Three field trials were conducted to investigate the effects of fluopyram alone or in combination with pre-plant sunn hemp cover crop, and azadirachtin combined with pre-plant sunn hemp on Rotylenchulus reniformis and Meloidogyne spp., and free-living nematodes. Zucchini (Cucurbita pepo) and tomato (Solanum lycopersicum) were grown in Trials I and II, and sweet potato (Ipomoea batatas) only was grown in Trial III. In all three trials, early applications of fluopyram at crop planting were effective in suppressing the abundance of Meloidogyne spp. (M. incognita and M. javanica) but it was not effective in reducing R. reniformis in the soil. Combining sunn hemp with fluopyram was suppressive to R. reniformis on short-term zucchini crop, but not on longer term tomato and sweet potato crops. In addition, application of fluopyram at transplanting was the key to successful suppression of Meloidogyne spp. as later fluopyram chemigation (at 2 weeks after planting in Trial II or 1 month after planting in Trial III) had no effect against Meloidogyne spp. On the other hand, planting of sunn hemp followed by monthly postplant azadirachtin application consistently suppressed R. reniformis, but this treatment did not suppress Meloidogyne spp. Integrating sunn hemp with fluopyram increased zucchini yield by >2.3 folds and that with azadirachtin increased the zucchini yield by >1.7 folds. Although no yield improvement was observed on tomato in Trial II, integrating sunn hemp with azadirachtin and fluopyram increased tomato yield by 0.23 and 1.12 folds, respectively, in Trial I. Marketable yield of sweet potato was increased by 4.5–6.4 folds in all the fluopyram treatments but was only increased 61.5% by sunn hemp plus azadirachtin treatment. While fluopyram alone often reduced the abundance of free-living nematodes, integrating with sunn hemp mitigated the negative impacts of fluopyram on soil health.