On Idaho wine grapes, sterol inhibitors were applied annually to an average 391 acres (173 base acres) between budbreak and veraison for control of powdery mildew.
If sterol inhibitors were unavailable, sulfur applications would replace 90% of the acre treatments of sterol inhibitors, and mineral oil (JMS Stylet-Oil) applications would replace 10% of the acre treatments. About 1.5 acre treatments of sulfur would be needed to replace one acre treatment of a sterol inhibitor. Mineral oil would be a 1:1 replacement.
Because sulfur must be applied more frequently than sterol inhibitors, applications are more likely to be mistimed due to weather conditions, equipment problems, and other scheduling conflicts. Where sterol inhibitors are replaced by sulfur, there would be an estimated 15% decrease in marketable yield in an average year. In a year when conditions are particularly conducive to mildew growth, the marketable yield loss might be 25%. Replacement of sterol inhibitors with mineral oil would not change yield. The overall cost (replacement compounds, increased applications, and yield loss) of replacing sterol inhibitors with sulfur and mineral oil is $54,000-$99,000 ($310 to $573 per base acre).
On Oregon wine grapes, sterol inhibitors were applied to 18,626 acres (7,100 base acres) between budbreak and veraison for control of powdery mildew. If sterol inhibitors were unavailable, sulfur applications would replace 75% of the acre treatments of sterol inhibitors and mineral oil (JMS Stylet-Oil) applications would replace 25% of the acre treatments. About 1.5 acre treatments of sulfur would be needed to replace one acre treatment of a sterol inhibitor. Mineral oil would be a 1:1 replacement.
Because sulfur must be applied more frequently than sterol inhibitors, applications are more likely to be mistimed due to weather conditions, equipment problems, and other scheduling conflicts. Where sterol inhibitors are replaced by sulfur, an estimated 30% decrease would occur in marketable yield in an average year. In a year when conditions are particularly conducive to mildew growth, the marketable yield loss might be 40%.
This yield loss is greater than it would be in Washington and Idaho because weather conditions in Oregon are more conducive to powdery mildew growth, resulting in higher disease pressure.
Replacement of sterol inhibitors with mineral oil would not change yield. The overall cost (replacement compounds, increased applications, and yield loss) of replacing sterol inhibitors with sulfur and mineral oil would be $3.40 million to $4.51 million ($500 - $664 per base acre).
On Washington wine grapes, sterol inhibitors were applied annually to an average 40,726 acres (12,226 base acres) between veraison and harvest for control of powdery mildew. If sterol inhibitors were unavailable, sulfur applications would replace 90% of the acre treatments of sterol inhibitors, and mineral oil (JMS Stylet-Oil) applications would replace the remaining 10% of the acre treatments. About 1.5 acre treatments of sulfur would be needed to replace one acre treatment of a sterol inhibitor. JMS Stylet-Oil would be a 1:1 replacement.
Because sulfur must be applied more frequently than sterol inhibitors, applications are more likely to be mistimed due to weather conditions, equipment problems, and other scheduling conflicts.
Where sterol inhibitors are replaced by sulfur, an estimated 15% decrease would occur in marketable yield in an average year. In a year when conditions are particularly conducive to mildew growth, the marketable yield loss might be 25%.
Replacement of sterol inhibitors with JMS Stylet-Oil would not change yield. The overall cost (replacement compounds, increased applications, and yield loss) of replacing sterol inhibitors with sulfur and JMS Stylet-Oil would be $4.09 million to $7.18 million ($334 to $587 per base acre). If sterol inhibitors were lost due to cancellation or resistance development, some wine grape growers would need to change their production practices, causing them to incur some additional one-time costs.
Currently, most Washington growers use wettable or micronized formulations of sulfur applied with a sprayer. If forced to rely on sulfur throughout the season for mildew control, they would probably need to use sulfur dust.
The dust formulations are more effective because the swirling action of the particles provides better canopy coverage. Sulfur dust also can be applied to a vineyard more quickly than a spray solution. A duster can cover 4.3 to 5.3 acres per hour and still give good coverage, while a sprayer can cover 1.5 to 2.2 acres per hour. Because sulfur must be reapplied at 7-to-10-day intervals (as opposed to 14-to-21-day intervals for sterol inhibitors), application speed would be important. The reason more growers do not currently use sulfur dust is that most of them do not own sulfur dust application equipment. With sterol inhibitors available, the improved coverage and faster application rate of sulfur dust is not worth the cost of a duster (about $8,800, including freight).
If sterol inhibitors were unavailable, one duster would be needed for approximately every 300 acres. Dusters would be purchased for use on at least 50% of the wine grape acres in the state, for a total cost of $205,000. This cost would not apply to Oregon or Idaho wine grapes; most Oregon growers have fewer than 50 acres, which could be covered with a sprayer, and most Idaho growers already use sulfur dust.
Because sulfur and JMS Stylet-Oil are not rainfast, it would be impractical to use them for season-long mildew control in vineyards irrigated by overhead sprinklers. About 35% of the wine grape acres in Washington, 60% of the grape acres in Idaho, and 5% of the grape acres in Oregon have overhead sprinkler irrigation. Growers with overhead sprinkler irrigation would be forced to convert to drip irrigation, at an average cost of $1,100 per acre. The total cost for this conversion would be $6.18 million.
Powdery mildew is not normally an economic problem in juice grapes. In 1995, however, weather conditions in Washington were so conducive to mildew growth that many juice grape vineyards had problems with mildew. The mildew fungus grew on the cluster stems of juice grapes late in the season, weakening connections between the berries and cluster stems. At harvest, berries on mildew-infected clusters fell on the ground ahead of the harvesting machines, causing a yield loss. It is not possible to estimate the economic value of the yield loss caused by mildew, because several frosts, which also contributed to weakening the cluster stems, occurred prior to juice grape harvest that year. In the future, it may be beneficial for juice grape growers to treat for mildew when weather conditions are particularly conducive to its growth. Sulfur is phytotoxic on juice grapes, so sterol inhibitors would be the only option. Therefore, loss of sterol inhibitors could result in yield losses for juice grape growers in some years.
Iprodione
On Oregon wine grapes, iprodione was applied to 6,988 acres (3,586 base acres) between bloom and harvest for control of botrytis bunch rot. If iprodione were unavailable, there would be no effective replacement compound.
Marketable yield would decrease 10% to 50%, depending on weather conditions. A 10% yield decrease would cause no economic loss, because the cost savings due to not applying iprodione would make up for the loss in yield. A 50% yield decrease would result in an overall cost of $5.50 million ($1,534 per base acre). See also Table 12.
| Table 12. Economic assessment for iprodione on Pacific Northwest wine grapes. | ||||||||||||||
| Active ingredient | Target pest | Acres treated | Base acres | Rate lb ai/A |
Treatments per year | Cost/A/ application |
Alternatives | Rate |
Cost/A/ |
Æ2 Control |
|
Æ Yield ($) |
Total impact3 (1000$) |
Impact/A4 ($) |
| Oregon wine grapes | ||||||||||||||
| iprodione | botrytis bunch rot | 6988 | 3586 | 1.0 |
1.9 |
$48.00 |
none | -- |
-- |
-193,644 |
10-50 |
0.2-5.69 |
0-5.50 |
0-1,534 |
| 1Costs shown are for the pesticides only. Labor and equipment costs are
about $6 per acre for each application. 2 Æ is a symbol that means "change in." 3Total impact is total cost to the growers, figured by adding Æ control costs and monetary Æ yield. A positive number is the cost to the grower. A negative number indicates a positive impact to growers. 4Total impact per base acre is the change in cost per acre to acres that have the pest problem and require use of the current pesticide." | ||||||||||||||
Botrytis bunch rot seems to be increasing in Washington and Idaho; loss of iprodione could adversely impact wine grape growers in those states in the future.
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