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 arid 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 P. 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 m2) 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 Polycarpaea-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. P. 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 arid land can be managed with certain weeds as a soil amendment
