Effect of spraying adjuvants with the biocontrol fungus Microsphaeropsis ochracea at different water volumes on the colonization of apple leaves

Abstract

In a previous study, it was observed that Microsphaeropsis ochracea was less efficacious as a biofungicide for apple scab when applied under field conditions as an unformulated spore suspension with an airblast spray using low water volumes as compared to a ground cover spray using high water volumes. The effect of spore concentration (10⁹ to 10¹² spores ha⁻¹), water volume (250–1500 L ha⁻¹), and 20 adjuvants were studied to improve colonization of apple leaves by M. ochracea. Using commercial-type spray equipment, the fungus was applied to excised apple leaves. Higher spores concentrations resulted in greater colonization. Water volume did not have a strong impact on colonization. Only a few adjuvants improved germination (glycerine) and mycelial growth (K-90, Agrimer, Ekol, and Tween 80) in some trials. When tested on apple trees, the adjuvant Assist provided the most consistent improvement in colonization in five out of eight trials. The use of oils, humectants, and surfactants could broaden the opportunities for using this biofungicide.

Keywords:

• Biofungicide
• adjuvants
• water volume
• Microsphaeropsis
• apple scab

Acknowledgements

We thank Philom Bios Inc. and the Agriculture & Agri-Food Canada Matching Investment Initiative for financial support; Byron Lee, Linda Van Heek, and Deanna Zimmerman for technical assistance, and Erin Cadieu for artwork.