Two temperatures (15 and 20 °C) and two levels of soil water potential (−0·0015 MPa and −0·001 MPa) were used to test the ability of a sterile red fungus (SRF) to protect wheat ( Triticium aestivum cv. Gamenya) and rye-grass ( Lolium rigidum cv. Wimmera) from infection by the take-all fungus ( Gaeumannomyces graminis var. tritici (Ggt)). The SRF protected wheat and rye-grass plants from infection by Ggt at both levels of soil moisture and temperature. The SRF promoted the growth of wheat and rye-grass in both the SRF alone and SRF + Ggt treatments at −0·0015 MPa and −0·001 MPa, and 15 and 20°. Shoot and root weights were greatest at −0·001 MPa and 15° for wheat, and −0·001 MPa and 20° for rye-grass, in all treatments. At both temperatures the percentage of dead plants of wheat or rye-grass was greater at −0·0015 MPa than at −0·001 MPa in the Ggt-alone treatment. The reduction of shoot and root weights of wheat and rye-grass by the take-all fungus was most severe at −0·0015 MPa and 20°. The SRF promoted the growth of the barley ( Hordeum vulgare cv. Stirling), great brome ( Bromus diandrus), chick pea ( Cicer arientinum cv. Opal), lupins ( Lupinus angustifolius cv. Yandee), medic ( Medicago polymorpha L. cv. Santiago), oats ( Avena saliva cv. Swan), peas ( Pisum sativum cv. Dundale) rape ( Brassica napus cv. Wesbrook), rye-grass ( Lolium rigidum cv. Wimmera) and subterranean clover ( Trifolium subterraneum cv. Nungarin) which are used as rotation crops with the wheat. Although the roots of all these plants were found to be infected and covered by the SRF, the recovery of the SRF was more frequent from the roots of wheat, rye-grass, oats, barley and great brome than peas, lupins, medic subterranean clover and chick pea.