Management of understorey to reduce the primary inoculum of Botrytis cinerea: Enhancing ecosystem services in vineyards

Botrytis bunch rot, caused by Botrytis cinerea (Pers.: Fr) is an important disease of grapevines that causes worldwide crop losses and reductions in wine quality. The pathogen predominantly overwinters on vine debris on the vineyard floor. In the current work, organic mulches were used to enhance biological degradation of vine debris to reduce levels of B. cinerea primary inoculum the following season. Four mulch types (anaerobically and aerobically fermented marc (grape pressings), inter-row grass clippings, and shredded office paper) were applied under 10-year-old Riesling vines in a 10-replicate randomized block design in New Zealand over two consecutive years. Plastic mesh bags, each containing naturally infected vine debris, were placed under vines on bare ground (control) and at the soil-mulch interface, in winter (July) 2003 and 2004. In each year, half the bags were recovered at flowering (December) and the remainder at leaf plucking (February), for assessment of B. cinerea sporulation from the vine debris and debris degradation rate. Bait lamina probes, which measure soil biological activity, were placed in the soil-mulch interface three weeks before each of the two bag-recovery dates in both years and were then removed and assessed at the same times as were the bags. All mulches led to a reduction in B. cinerea sporulation. This reduction was significantly correlated with elevated rates of vine debris decomposition and increased soil biological activity. Over both years, compared with the controls, all treatments gave a 3- to 20-fold reduction in B. cinerea sporulation, a 1.6- to 2.6-fold increase in vine debris degradation and in the two marc and the paper treatments, a 1.8- to 4-fold increase in activity of soil organisms. These results show the potential of enhanced soil organism activity in the soil for disrupting the B. cinerea life cycle. The implications of these results for infection levels of grapes are currently being investigated.