Effect of nitrogen, fungicide and pruning on Botrytis cinerea in raspberry

Magdalena Cruz A.1

Botrytis cineres, causal agent of the grey mould, is a major raspberry pathogen in Chile. Economic damage occurs mainly on harvested berries. It is know that chemical control of the disease in raspberry in the field is partially successful, but on the other hand, references report that very slight changes in temperature and humidity in grapevine canopy are related to differences in botrytis severity. This experiment was carried outto study the growth of B. cineres in raspberry, cv. Heritage, when the canopy has been modified by thinning primocanes and reducing the nitrogen rates, as well as fungicides applications. Two levels of nitrogen (80 and 240 kg ha N), two levels of primocanes thinning and two levels of fungicide spray (with and without applícatios) were combined in a factorial arrangement. The field trial was a randomised complete block design, with live replícates. The disease was measured by the amount of infected berries and by the conidia production either in ripe and unripe berries, during the whole harvest periodo The results were expressed as area under the disease progress curve. Fungicide treatment signilicantly decreased (P < 0.001) the conidia number in ripe and unripe berries, and the percentage of infectad berries. The pathogen was observad on the necrotic flower parts during the whole harvest periodo There was a significant correlation betw6en the amount of conidia on unripe berries and the percentage of infected fruits after harvest (r = 0.96; P < 0.001). The results agree with earlier reports holding that a high percentage of berries are infected after harvest when the inoculum has been kept in necrotic styles, where fungicide cannot arrive. Raspberry grey mould was not significantly affected by canopy modilications, under a dry summer.

Keywords: botrytis, Botrytis cineres, grey mould, raspberry, Rubus idseus, fungicide.
1 Estación Experimental Quilamapu (INIA). Casilla 426, Chillán, Chile.