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The effectiveness of certain on-farm weeds as soil amendments was ascertained against Macrophomina phaseolina, a soil-borne pathogen causing dry root rot of crops grown under rainfed conditions in and regions. Population changes in M. phaseolina were determined in soils amended separately with residues (1%, w:w) of Aerva persica, Celosia argentea, Corchorus depressus, Euphorbia hirta, Heliotropium subulatum and Polycarpaea corymbosa, for a period of 90 days. Significant reductions by 90.4-100% in the population of M. phaseolina were achieved with all the weed residues except R corymbosa. Celosia and Euphorbia residues completely eradicated viable propagules of M. phaseolina. A strong increase (44-61%) in the population of antagonistic actinomycetes was also found in soil amended with Corchorus and Euphorbia. In field tests, soil amended (50 g m(2)) with Euphorbia, Aerva and Celosia residues significantly reduced dry root rot incidence on clusterbean and also reduced M. phaseolina propagules in the soil. However, dry root rot incidence in Polyearpaea-amended soil (5.8-24.6%) was not significantly different from that in non-amended soil (4.3-25.3%) in both years of the experiment. R corymbosa also increased the number of propagules of M. phaseolina in the soil. The results demonstrate that dry root rot of rainfed-cultivated annual crops in and land can be managed with certain weeds as a soil amendment.