Application of chemical and biological agents for the management of frosty pod rot (Moniliophthora roreri) in Costa Rican cocoa (Theobroma cacao)

Abstract

AbstractThis article describes two field trials carried out at La Lola, Costa Rica, to assess control measures against frosty pod rot of cocoa (Theobroma cacao) caused by Moniliophthora (Crinipellis) roreri. In the first, factorial, trial the control agents were applied using motorised mistblowers (MMs) and hydraulic sprayers fitted with a narrow angle cone nozzle. There was an interaction between agents and application methods; together with previous application data for the most active fungicide (copper hydroxide), these trials indicate that best yields are achieved with sprays that maximise deposits on pods. We describe the droplet size spectra produced by a Stihl SR400 MM under a range of conditions because this has become the standard method of fungicide application in this series of trials at La Lola. The factor that had the largest effect on droplet size spectrum was the presence or the absence of a detachable baffle plate in front of the air‐shear nozzle. In both trials described here, MMs were fitted with baffle plates, a formulation pump and restrictor transmitting 550 mL min−1 to deliver an estimated equivalent of 190 L ha−1. Copper hydroxide as prophylactic applications at 1500 g a.i. ha−1 have, to date, shown the most consistent (but incomplete) improvement in healthy pod yield. Use of copper fungicides may be cost effective when farm‐gate cocoa prices exceed approximately $1.25 kg−1. In these trials, isolates of the hyperparasitic fungi Clonostachys byssicola and Trichoderma asperellum and two off‐patent triazole fungicides (bitertanol and triadimenol) made no significant improvement to healthy yields. The systemic oxathiin fungicide flutolanil, at a dosage of 300 g a.i. ha−1, appears to protect pods substantially at early stages but gives proportionately less control of M. roreri than copper at later stages of pod development.