Fungicides for control of flower and berry infections of Botrytis cinerea in boysenberry

During 1998-2002 in New Zealand, fungicides were evaluated on boysenberry (Rubus spp. hybrid) for control of Botrytis cinerea in the laboratory (detached flowering lateral assay), and in the field (two small scale field evaluations and one large scale grower trial). Fungicides used were thiram (standard grower control), pyrimethanil, cyprodinil+fludioxonil, fenhexamid and three undisclosed plant extracts. Laboratory studies showed that fungicides, except for two plant extracts, reduced flower infections. Disease incidence was also affected by the timing of fungicide applications in response to artificial flower inoculations with B. cinerea conidia. In the field, all fungicides reduced B. cinerea berry infections, however some products (pyrimethanil, cyprodinil+fludioxonil, plant extract) affected plant growth and/or berry quality and their use was discontinued. Further grower trials of fenhexamid in comparison to standard fungicide applications (grower control) and an unsprayed control on four commercial properties showed that fenhexamid achieved similar reductions in disease levels as the grower control. The fenhexamid residue decay curve followed a first order kinetics with less than 0.05 mg/kg fenhexamid detected in fruit at harvest. The research contributed to the registration of fenhexamid for use in New Zealand boysenberry.