Biopesticide and biofertilizer potential of tropical earthworm vermicast tea

The adverse effects of chemical pesticides have continued to drive the search for safe, biological alternatives. Studies on biopesticide potential of earthworm casts have remained largely limited to those of temperate earthworms. We evaluated the insect pest repellency and growth-promoting potential of tropical earthworm-derived vermicast tea on the seedlings of Arachis hypogaea (groundnut), Zea mays (maize) and Phaseolus vulgaris (bean). Field-sourced earthworm casts were soaked in water for 48 hours, routinely stirred every 6 hours, and filtered through a fine mesh cloth. The filtrate was the vermicast tea. Seedlings grown in garden soil were sprayed with vermicast tea every four days. The seedlings were monitored for insect pest-induced leaf damage and growth performance for 5 weeks. Vermicast tea exhibited insect pest repellency effect on groundnut and bean seedlings, as evidenced by the significantly lower (p<0.01) insect pest attack on the treated seedlings, as against the untreated that recorded high pest infestations. However, leaf damage was relatively low in maize seedlings, and the differences in percentage leaf damage among the treated and untreated were not significant (p>0.05). The effect of vermicast tea on the physical growth of seedlings was positive, but marginal. This result calls for increased research on tropical earthworms.