A strategic review: The first step in establishing low input viticulture regimes rationalising powdery mildew control in Riverland vineyards

Abstract

Most Riverland vineyards are sprayed frequently to control powdery mildew but a single spray of sulphur across the region cost nearly $1m. In efforts to reduce these costs, improve control of the disease with fewer sprays and reduce the carbon footprint in vineyards, spray diary records for several varieties for season 2006/07 were overviewed.

Summary

In an effort to reduce costs, improve control of the disease with fewer sprays and reduce the carbon footprint in vineyards, spray diary records from CCW Ltd, Berri, SA, and McGuigan’s Wines, Loxton, SA, for several varieties for season 2006/07 were overviewed. Several thousand individual patch records were assessed initially, prior to a sub-sample of 137 Chardonnay spray diaries being reviewed in more detail. To assist this review, a vineyard spray program evaluator was devised and used to rapidly assess the effectiveness of sprays applied. Disease scores from the evaluator were compared with in-field disease assessment ratings made by wineries just prior to harvest.

Generally speaking the spray programs listed in the diaries controlled powdery well with minimal impact on the sale of the crop. An average of 7 sprays were applied/season. There was however, a large range in the number applied (from 2 to 13 sprays were applied in that season) with varying degrees of success in controlling powdery from within that range. Some growers achieved excellent control with as few as four sprays, while others sprayed twelve or more times and achieved poor control. There was no correlation between the number of sprays and the level of control.

Only a few patches (6% in number, accounting for 3% of the area) had levels of disease sufficient for the winery to reject the crop. This means that most growers did an acceptable or better job in controlling the disease, even though the outcome might have been achieved with fewer sprays.

Most growers (73% of the patches, accounting for 81% of total area surveyed) applied less than eight sprays but had insignificant amounts of mildew in their vineyard patch pre-harvest. More sprays were not better meaning that, on average, no better control of powdery was achieved by the application of more sprays. This suggests that the additional sprays applied by the 25% of growers, were unwarranted.