A greenhouse study was carried out to evaluate the effects of temperature,
soil moisture, soil texture, fertilization, and intercropping on susceptibility of the
Egyptian cotton cultivar Giza 75 to Macrophomina phaseo/ina. The obtained results
revealed that the optimum temperature of pathogenicity was somewhere between
24.5±1 .50C to 38.0±.2.0oC. The results were inconclusive in determining the
relationship between soil moisture content and susceptibility of cotton to M.
phaseolina. The discrepancy in the results may be attributed to the fact that the effect
of soil moisture was obscured by other environmental factors interacting with soil
moisture. The results suggest that cotton is more susceptible to M. phaseo/ina in clay
soil than in sandy clay soil. Nineteen fertilizer treatments were evaluated as to their
effects on susceptibility of cotton to M. phaseolina. Of these treatments, six were
effective in reducing the development of M. phaseo/ina lesions on tap root. However,
of the six treatments, the combination of calcium nitrate, potassium sulphate, and
calcium superphosphate was the best for two reasons. First, this combination reduced
the development of M. phaseolina lesions on tap root by 71.86%. Second, this
combination was nutritiously balanced because it provided cotton with NPK. Although,
other treatments were as effective as this combination in reducing the diseases, they
were nutritiously unbalanced. Intercropping onion (Giza 6) and Chinese garlic with
cotton significantly suppressed the advancement of M. phaseolina lesions on cotton
stem by 80.59% and 83.01 %, respectively.