Research to control Cotton Black Root Rot in California has focused on cultural control because chemical control has not provided adequate protection under the adverse climatic, edaphic and inoculum pressure we often experience. One of our research objectives has been to identify the interactive role these three stresses play in retarding cotton growth and delaying maturity. ln l984 we initiated a date of planting trial to assess the sensitivity of Cotton Black Root Rot damage to climate. That year experienced below normal temperatures during April and only by the May 10 planting date did temperatures warm sufficiently to reduce the stunting from Black Root Rot. The earlier planting dates gave cotton stands that remained stunted for one month past the cessation cool temperatures. This trial was repeated in 1985. The first two weeks in April temperatures were in the 90's, which raised soil levels 7 degrees F above the previous year for the month of April. Despite severe tap root necrosis due to the presence of Thielaviopsis basicola, plants in 1985 were not stunted compared to the control. An abundance of lateral roots was observed in the diseased plants. The two years data support the observation of Arndt (Plant Disease Reporter - Supplement 1957) who showed an abrupt temperature threshold for the stunting due to Thielaviopsis basicola, while the plant death from Pythium ultimum and Rhizoctonia solani gradually diminished with increasing temperature.