The Effects of a Fungal Biocontrol Agent and a Chemical Adjuvant on the Efficacy of Cuprous Oxide Sprays for Controlling Witches’ Broom Disease in Cocoa

• Main Authors: J.R.M. Thacker, L.V. Laine, R.D. McLean
• Format: Article
• Language: English
• Published: Sultan Qaboos University 2000-01-01
• Series: Journal of Agricultural and Marine Sciences
• Subjects: science
• Online Access: https://journals.squ.edu.om/index.php/jams/article/view/565

A Field experiment was carried out in a cocoa plantation in Brazil to evaluate whether a fungal biocontrol agent (Trichoderma spp.) and a chemical adjuvant could enhance the efficacy of cuprous oxide sprays that are applied to control witches’ broom disease. The experimental design was comprised of 16 plots containing approximately 50 mature cocoa trees each. Each plot measured approximately 1000 m2. Treatments were allocated to plots randomly. Treatments were: control (no spray), cuprous oxide, cuprous oxide plus adjuvant, and cuprous oxide plus adjuvant plus fungus. Sprays were applied monthly from April to September in line with official recommendations for the control of witches’ broom disease. Sprays were applied using a motorized backpack mistblower. Monthly assessments of disease incidence were made from March to November. Assessments were made on five randomly selected trees from 15 marked trees located in the center of each plot. Assessments were comprised of the numbers of healthy and diseased pods observed on trees, the numbers of green and necrotic axillary and terminal brooms, and the numbers of healthy and diseased pods taken from trees at each harvest. The results show that disease incidence was the highest in the control plots where the fewest healthy pods were harvested. The overall incidence of disease varied from 25 to 45% across all treatments. Statistically, the results show that there were no significant differences among treatments, including the control. No significant improvements in the efficacy of copper-based sprays were measured as a result of adding the fungus or the adjuvant to the spray. Also, no significant improvements in disease control were recorded when using cuprous oxide on its own. We concluded that copper sprays were ineffective in controlling the disease. This paper discusses our results in the light of official recommendations for the control of the disease.