Suppressing Sting Nematodes with Brassica sp., Poinsettia, and Spotted Spurge Extracts

Abstract

With synthetic nematicide options becoming limited, two studies were initiated to investigate the usefulness of selective botanical extracts for the suppression of sting (Belonolaimus longicaudatus Rau) nematodes. Plant materials were from greenhouse‐grown mature specimens of spotted spurge (Chamaesyce maculata L. Small); poinsettia (Euphorbia pulcherima Willd. ‘Freedom Red’); lantana (Lantana camara var. hybrida); mature, field‐grown tall lettuce (Lactuca canadensis L.); and goldenrod (Solidago altissima L. var. scabra), plus a seed meal extract from Brassica juncea ‘Pacific Gold’ (BSM). Nematodes were exposed to 1.2‐mL extract of either shoot or roots of each plant species. Nematode mortality counts were made daily for 4 d. In Study 1, effects of botanical extracts on nematode mortality were evaluated when applied directly to laboratory‐controlled sting nematode populations in test tubes. Root extracts of spurge, poinsettia, and lantana provided 69, 70, and 57% mortality, respectively, by 96 h while goldenrod and tall lettuce root extracts and the untreated provided 0% mortality. Shoot portions of poinsettia and spurge provided 95 to 98% mortality while goldenrod, tall lettuce, and lantana shoot extracts had 64, 40, and 25% mortality, respectively. Greenhouse studies evaluated the most successful laboratory extracts in a soil environment and included poinsettia shoot extracts and BSM. Poinsettia shoot extracts with irrigation provided 70% control compared with the untreated pots while poinsettia nonirrigated provided 73% control. Brassica sp. seed meal with irrigation provided 92% control while BSM nonirrigated provided 99.5% control. Brassica sp. seed meal, poinsettia, and spurge shoot extracts showed most promise as possible biocontrol agents of sting nematodes.