Ma. Verhaar et al., Improvement of the efficacy of Verticillium lecanii used in biocontrol of Sphaerotheca fuliginea by addition of oil formulations, BIOCONTROL, 44(1), 1999, pp. 73-87
Biocontrol of cucumber powdery mildew, Sphaerotheca fuliginea, by Verticill
ium lecanii is seriously hampered at low humidities. The effect is especial
ly marked at low humidity (60% RH) during the three hours following the app
lication of V. lecanii spores suspended in water. Formulations of V. lecani
i spores in oil might improve the situation. Arachid oil (peanut oil) and t
wo invert emulsions using either Sunspray 6N or paraffin oil were tested in
formulations of V. lecanii spores. Arachid oil gave the best development o
f V. lecanii on mildewed cucumber leaves. V. lecanii formulated with arachi
d oil showed significantly better control of mildew than without. A concent
ration of 0.5% arachid oil was somewhat toxic to mildew but 0.05% was not.
Arachid oil did not show toxicity to V. lecanii. The humidity requirements
of V. lecanii formulated with and without 0.05% arachid oil were compared a
t 95, 90 and 85% RH. Arachid oil significantly reduced the humidity depende
nce of V. lecanii. Since arachid oil is safe for human consumption and not
phytotoxic to cucumber leaves, low concentrations of arachid oil are recomm
ended as an additive to increase the effectiveness of V. lecanii as a bioco
ntrol agent of S. fuliginea.