| Plant-parasitic nematodes cause serious yield reductions in agricultural crops ranging from 8 to 20% worldwide. Alternative practices to the use of broad-spectrum synthetic pesticides for the management of phytonematodes in agricultural crops are receiving increasing attention. Organic amendments and naturally occurring aromatic compounds represent a more acceptable ecological practice for control of phytonematodes in agricultural soils. Five organic amendments (velvetbean, kudzu, pine bark, paper waste, and urea-N), and three naturally occurring aromatic compounds (benzaldehyde, furfural, and citral) were evaluated for the management of plant-parasitic nematodes under greenhouse conditions. The amendments were applied to soil at rates ranging from 0 to 5% (w/w), while aromatic compounds were used between 0 and 500 The effects of combinations of the organic amendments and benzaldehyde on phytonematodes, microbial activity, and soil enzymes were also studied. These combinations were synergistic in reducing phytonematode populations, but populations of non-parasitic nematodes, bacteria, and fungi were significantly increased by most combinations. Control soils contained a predominantly Gram-negative bacterial flora while benzaldehyde in combination with velvetbean or kudzu, promoted Gram-positive bacteria. Fungal genera stimulated by benzaldehyde and amendments included species of Aspergillus, Myrothecium, Penicillium, and Trichoderma. Soil enzymatic activities were directly correlated with bacterial and fungal populations throughout the experiment but were negatively correlated with number of phytonematodes at the end of the experiment.Analyses of microbial populations through sequential sampling provided valuable information about the activities and changes in size of specific groups of microorganisms after treatment with amendments and benzaldehyde. Results indicated that stimulation of an antagonistic microflora, and release of toxic substances (e.g., ammonia), during decomposition of organic matter and aromatic compounds were some of the mechanisms involved in suppression of plant-parasitic nematodes. |
