Aiming for the bullseye on target spot management in tropical cotton: insights from 2025 fungicide screening trials

Abstract

Target spot, caused by Corynespora cassiicola, is a foliar fungal disease that can afflict cotton production in Australia’s tropical regions. In the pursuit of potential management options, the performance of various fungicide treatments, including Merivon® and Belanty® (currently under minor use permit), Orius® 430, Product A, and a positive control product, used internationally, were assessed. Efficacy was measured by scoring severity in terms of disease progression and target spot-induced leaf senescence resulting in premature defoliation. Results showed that Merivon® (fluxapyroxad + pyraclostrobin) and the positive control achieved the lowest defoliation across several trial sites (e.g. 4.5–10.4% vs 27–38.9% in untreated controls). Product A was statistically comparable to the positive control, although defoliation was numerically higher. Belanty® (mefentrifluconazole) showed variable efficacy, while Orius® 430 (tebuconazole) lacked efficacy. Yield impact was evaluated at one site in Queensland, but no significant treatment effect was detected, due to spatial variability and poor weather conditions that caused extensive fruit shedding. Across all sites, disease onset occurred after canopy closure despite abundant rainfall prior, suggesting canopy development is a key driver for target spot epidemics. Future research aims to better understand canopy factors in relation to disease outbreak and to quantify yield impact to support an integrated disease management approach