Four day/night temperature regimes (11/6, 14/9, 17/12, 20/15 °C), three photoperiods (0, 12, 24 h d−1), and four continuous temperature regimes (10, 13, 16, 19 °) were evaluated for their effects on growth, sporulation, and conidia discharge of two isolates of Valdensinia heterodoxa, a foliar pathogen of salal (Gaultheria shallon). All temperature regimes supported mycelial growth; however, growth rates were faster at higher temperatures. Sporulation and conidia discharge in both isolates was generally highest at 17/12 ° (day/night) or 16 ° constant compared with other temperature regimes. Photoperiods of 12 and 24 h d−1 resulted in faster growth and significantly greater sporulation and discharge compared with a continuous dark treatment. The study shows that temperature and light conditions have a moderate effect on mycelial growth but are crucial for sporulation of V. heterodoxa. Possible implications for the use of V. heterodoxa as a potential biological control agent for salal are discussed.