Fusarium crown rot (FCR) caused by Fusarium pseudograminearum (Fp) and F. culmorum (Fc) and Rhizoctonia root rot caused by Rhizoctonia solani AG8 (Rs8) and R. oryzae (Ro), are major soil-borne fungal diseases responsible for economic losses in dryland wheat in the Pacific Northwest region of the US. This study focuses on exploring the finer details of soil moisture and temperature impacts on these four pathogens and, develop models for projecting their growth in response to these variables. Methods were developed using NaCl, KCl and polyethylene glycol to precisely define water potential (WP) treatments at different temperatures. On defined media and sterile wheat straw, the optimum temperature for the mycelial growth and dry weight gain for Fc and Rs8, and Fp and Ro was 20-25°C and 25-30°C, respectively. The optimum WP was -0.3 MPa for both Rhizoctonia spp. and -1 to -2 and -2 to -3 MPa for Fc and Fp, respectively. Macroconidia of Fusarium spp. were capable of germinating across all ranges of WP, even the driest. In soil, except for Fp, the other three pathogens had different optimal temperatures and WPs for their growth, as measured by DNA concentrations quantified by real-time PCR. The optimal temperature and WP for both Rhizoctonia spp. were 10-15°C and -2 MPa, respectively. Fc had a temperature optimum of 10-15°C with a preference for the driest WP ranges below -5.5 MPa. Fp was restricted to a narrow range of WP from -1.43 to -3.12 MPa. In a greenhouse study, the increase in Fp DNA in the infected wheat plants was strongly negatively correlated to the median values of WP in the whole column. FCR disease score in Fp inoculated columns was negatively correlated with the WP at depths where roots would be active. On the other hand, there was no significant difference of DNA and FCR disease score in Fc inoculated columns with the WP levels. Models were developed for projecting pathogen growth in defined nutrient media, soil, and infected plants based on the temperature and WP levels.