Control of powdery mildew and black spot on roses with petroleum spray oil

O. Nicetic, D.M. Watson and G.A.C. Beattie, Centre for Horticulture and Plant Sciences, University of Western Sydney Hawkesbury, Locked Bag 1, Richmond, New South Wales 2753, Australia.


The C24 petroleum spray oil, Ampol D-C-Tron Plus, was evaluated for control of powdery mildew and black spot on roses at three commercial cutflower and nursery facilities around Sydney. Prophylactic and therapeutic control of powdery mildew using petroleum spray oil (PSO) was evaluated under greenhouse conditions on rose cultivars Bridal Pink and Sonia while prophylactic control of black spot was assessed in an outdoor nursery on cultivars Friendship and Tournament of Rose. PSO concentrations of 0.5% and 1.0% (v/v) were evaluated for both diseases, and combinations of 0.5% and 1.0% oil with 0.063 M NaHCO3 were also evaluated for black spot.

Spray intervals of 7, 14 and 21 d were examined to determine which gave the best control of powdery mildew. Good levels of prophylactic and therapeutic control of powdery mildew were achieved with 0.5% and 1.0% PSO. Similar levels of control were achieved with sprays applied at 7 and 14 d intervals but intervals of 21 d allowed some redevelopment of disease. Incidence of black spot were lower using 1.0% PSO and the addition of NaHCO3 had no practical benefit for black spot control over 1.0% oil alone. However, the addition of NaHCO3 improved the efficacy of 0.5% PSO. Results suggest that PSO provide sustainable and cost-effective control of powdery mildew and black spot.


Plant Protection Quarterly (1999) 14 (4) 131-135.