Australian grapevine yellows – Source and spread

Abstract

Australian grapevine yellows - Source and spread

Summary

The work undertaken in this project has led to a better understanding of AGY by Riverland grapegrowers and hopefully brought a clearer understanding of what is AGY and what is not. As a result, it perhaps has led to some reduction in anxiety about the disease.

The monitoring of levels of AGY and subsequent investigations into the disease during 2001/02 revealed some distinguishing aspects of the epidemiology of AGY. This has precipitated a revision of the directions of further investigation. The strong association between high levels of AGY in vineyards and the proximity of marshlands and permanent still/shallow water is a significant finding. This should reduce the time and cost of resolving the source of AGY and how it spreads into vineyards.

Data from this project provided evidence contrary to the notion that commercially significant quantities of AGY are introduced to vineyards by propagation material. Additionally, evidence is presented contrary to the idea that AGY spreads from weed hosts or from previously affected vines. In contrast, evidence supports the notion that AGY is native to Australasia, that the pathogen is resident in native plants and these hosts occur in some form more prevalent or grow more favourably at locations external to vineyards. It appears that these locations provide the main source of AGY.

These supposed native hosts of AGY have not yet been identified but the number of likely candidate species has been reduced from 1000’s to a few (5-10 species) and their location has been delimited to a zone within a 900m radius of permanent still/shallow water near severely affected vineyards. These zones need immediate exploration in pursuit of infected native plant hosts with view of locating the supposed leafhopper vector(s) of AGY on those plants.

Assessment of the extent and severity of AGY was also made. AGY was found in virtually all vineyards older than three years. The relatively high number of vineyards in which some yield loss was found may lead to a reappraisal (upward) of the importance of the disease to the grape industry. This is especially true for cv. Chardonnay in the Riverland.

Communication about means of identifying AGY and information about its source and spread has been made with grapegrowers in the Riverland. It is recognised that this is an ongoing process and that considerable confusion remains in the Riverland (and the Australian) industry as to what is AGY, how is it distinguished from restricted spring growth (RSG), late season leaf curl (LSLC) and another disorder for which the name scaly bark stunt (SBS) is proposed. The confusion needs to be allayed by further investigation (as above) and by effective communication of the outcomes of that work.

The present work provided evidence of specific localities in the Riverland that should be further investigated to locate the source and spread of AGY. It highlighted the need for these investigations before a new wave of the epidemic increases losses in the Riverland or other regions and emphasises the need for further attention to communicating about AGY to grapegrowers the Riverland (and Australia).