Development of an eradication strategy for exotic grapevine pathogens

22 - 24 September 2009

Eradication of exotic grapevine diseases can incur significant costs to growers and the industry using current strategies which include complete removal of affected and suspected vines. Alternative strategies need to be developed which optimise efficiency of the eradication process and minimise the economic cost of returning the crop to its previous quality and production levels. The endemic disease of grapevine, black spot (Elsinoe ampelina), was used as a model to develop a drastic pruning eradication strategy for the exotic disease black rot (Guignardia bidwellii). These pathogens have similar biology and epidemiology and inhabit fruit, leaves and shoots of grapevines.

A trial was established in the Sunraysia district of Victoria in 2006 to develop and assess a drastic pruning protocol for disease eradication. The trial comprised four table grape cultivars as blocks and plots consisted of three vines with spacing of at least seven metres between plots. Vines in each plot were either drastically pruned (as described below) or left as controls with standard two-bud spur pruning. All vines were inoculated in spring 2007 and developed black spot leaf lesions and stem cankers by the following summer.

Vines in treated plots were cut off at the crown with a chainsaw in July 2008. All excised material from above the crown was placed in an excavated pit about 25 metres from the trial. The vineyard floor around the treated vines was raked and the debris was placed in the excavated area to be burnt and buried. Soil between vines was disc cultivated to bury any remaining debris. Trunks of the treated vines were drenched with lime sulphur using a backpack sprayer to reduce the likelihood of inoculum developing from any infected debris lodged in the bark.

In December 2008, symptoms were recorded on all control vines and on four of 36 treated vines. On treated vines, each symptomatic shoot grew from the trunk within 20 centimetres of the ground. A bioassay conducted on vine debris sieved from the soil below vines indicated that symptoms on treated vines were caused by inoculum produced from the debris. Monitoring of potted sentinel vines placed strategically within and around the trial site during spring and early summer revealed that there was no spread of disease between plots or from external sources.

As a result of this first simulated eradication, the protocol was modified to include removal of lower shoots and the use of straw mulch on the vineyard floor as a barrier to inoculum spread and to accelerate decomposition of debris. The revised protocol will be applied in the second year of the eradication trial in Australia. Validation of the protocol for eradicating black rot has been initiated in an infected vineyard in New York USA, where the disease is endemic. This research has potential to save the Australian wine industry over $18 million in lost production and vineyard re-establishment if there is an exotic disease incursion.