Nematicidal Performance of Ipomoea carnea and Pluchea dioscoridis Extracts towards Tylenchulus semipenetrans and their Possible Application in Nematode Management on Washington Navel Oranges

Crude methanolic shoot extracts of the perennial weeds, Ipomoea carnea and Pluchea dioscoridis were tested for their nematicidal activity towards second stage juveniles (J₂s) of the citrus nematode, Tylenchulus semipenetrans under laboratory conditions. All extracts at the concentrations 100, 250, 500, 1000 and 2000 mg/L significantly suppressed J₂s viability causing mortality ranged from 13.82 to 100% as compared to check and blank treatments. Mortality (%) of J₂s was linearly increased with increasing concentrations of plant extracts. Extract of P. dioscoridis (LC₅₀ = 249 mg/L) appeared to be stronger than I. carnea (LC₅₀ = 345 mg/L). Results of GC-MS analysis of I. carnea and P. dioscoridis extracts revealed the presence of 33 and 36 different chemical compounds, respectively. The most prevalent compounds present in I. carnea extract were Cyclopentane, 1-acetyl-1,2 epoxy, 2-Octenal, (E) and Thymol, whereas Ethanone, 1-(2-methylcyclopropyl)-, Cholestan-3-ol, 2-methylene-, (3á,5à)-, cis-5,8,11,14,17-Eicosapentaenoic acid and Undecanoic acid were the most occurred in P. dioscoridis extract. Soil application with I. carnea and P. dioscoridis extracts alone at their LC₉₅ values (1637, 1340 mg/L, respectively) and in their combination at half LC₉₅ values of each (819 and 670 mg/L for I. carnea and P. dioscoridis, respectively) and with the chemical nematicide Oxamyl 24% SL at the recommended dose (3 L/feddan) significantly reduced final population densities (Pf) and reproduction factor (Rf) of T. semipenetrans during two subsequent growing seasons (March-September, 2023 and 2024) on Washington Navel orange trees growing in an orchard at Rosetta province, Behera governorate. Oxamyl 24% SL achieved a valuable reduction of Pf reached to 84.07% and 81.08% for the 1^st and 2^nd seasons, respectively, whereas extracts of I. carnea, P. dioscoridis and their combination provided considerable reduction levels of nematode Pf ranged between 79.03-86.48% and 75.64-84.01% for the 1^st and 2^nd seasons, respectively. It is worthy to note that Co-toxicity factor of the combination of the two extracts recorded the values (-10.2 and -11.87) for the 1^st and 2^nd seasons, respectively that means there is an additive effect between each other. All extracts alone and their combination appeared to be effective as Oxamyl 24% SL recording a considerable relative nematicidal efficacy (%) ranged from 93.3 to 103.6% of the chemical nematicide. This finding introduced these extracts as promising natural alternatives to Oxamyl that hope to be environmentally safe in the future.