Biologic and Economic Assessment
Insecticides
Dimethoate
On all Pacific Northwest grapes, dimethoate was applied annually to 6,517 acres (6,315 base acres) in the summer for control of leafhopper and thrips. Most applications were on Washington wine grapes. If dimethoate were unavailable, growers would replace it with imidacloprid, carbaryl, endosulfan, malathion-methoxychlor, and azinphos-methyl.
The alternatives used would depend on the primary target pest. One application of dimethoate would be replaced by one application of imidacloprid. The other alternatives are less effective against leafhopper and thrips; it would take 1.2 to 1.5 applications to replace one application of dimethoate.
No change would occur in yield or quality where any of the alternatives are used. The overall cost (replacement compounds plus increased applications) of replacing dimethoate with imidacloprid, carbaryl, endosulfan, malathion-methoxychlor, and azinphos-methyl would be $164,000 ($26 per base acre). See also Table 4.
On Idaho wine grapes, dimethoate was applied annually to an average of 97 acres (97 base acres) in the summer for control of leafhoppers and thrips. About 40% of these treatments were primarily for leafhoppers, and 60% were primarily for thrips.
If dimethoate were unavailable, the alternatives used would depend on the primary target pest. On the acres where leafhopper is the primary target, imidacloprid applications would replace 75% of the acre treatments of dimethoate and carbaryl would replace 25% of the acre treatments. One application of imidacloprid would replace one application of dimethoate.
Carbaryl is not as effective on leafhoppers as dimethoate; 1.5 applications of carbaryl would be needed to replace one application of dimethoate. Imidacloprid is not yet labeled for thrips control and questions are raised about its efficacy against thrips; carbaryl would replace 100% of the acre treatments of dimethoate on acres where thrips are the primary target. Imidacloprid might be an alternative in the future if it proves to be effective against thrips.
No change in yield or quality would occur where any of the alternatives are used. The overall cost (replacement compounds plus increased applications) of replacing dimethoate with carbaryl and imidacloprid would be $4,000 ($41 per base acre).
On Oregon wine grapes, one grower applied dimethoate to 431 acres (431 base acres) in 1995 for control of leafhoppers and thrips. This vineyard was in the Columbia Valley in eastern Oregon, where conditions are nearly identical to those in eastern Washington. This application was atypical of Oregon viticultural practices as leafhopper and thrips generally are not considered economic pests in that state. Therefore, loss of dimethoate would have a negligible impact in Oregon.
On Washington wine grapes, growers applied dimethoate to an average 5,035 acres (4,833 base acres) annually in the summer for control of leafhoppers and thrips. About half of these treatments were primarily for leafhoppers, and half were primarily for thrips.
If dimethoate were unavailable, the alternatives used would depend on the primary target pest. On acres where leafhopper is the primary target, imidacloprid applications would replace 75% of the acre treatments of dimethoate. Carbaryl and malathion-methoxychlor applications would each replace 10% of the acre treatments, and endosulfan applications would replace 5% of the acre treatments.
One application of imidacloprid would replace one application of dimethoate. The other three alternatives are less effective on leafhoppers; 1.5 applications of carbaryl, 1.2 applications of malathion-methoxychlor, or 1.2 applications of endosulfan would be needed to replace one application of dimethoate.
Imidacloprid is not yet labeled for thrips control, and questions arise about its efficacy on thrips. On acres where thrips are the primary target, endosulfan applications would replace 65% of the acre treatments of dimethoate. Carbaryl applications would replace 30% of the acre treatments, and azinphos-methyl applications would replace 5% of the acre treatments. Imidacloprid might be an alternative in the future if it proves to be effective against thrips. None of the alternatives are as effective on thrips as dimethoate; 1.2 applications of endosulfan or 1.5 applications of carbaryl or azinphos-methyl would be needed to replace one application of dimethoate.
No change would occur in yield or quality where any of the alternatives are used. The overall cost (replacement compounds plus increased applications) of replacing dimethoate with imidacloprid, carbaryl, malathion-methoxychlor, endosulfan, and azinphos-methyl would be $160,000 ($33 per base acre).
Carbaryl
On all Pacific Northwest grapes, carbaryl was applied to an average 2,566 acres (2,448 base acres) annually in the spring and summer for control of leafhopper and cutworm. If carbaryl were unavailable, the alternatives would depend on the primary target pest.
Where leafhopper is the primary target, imidacloprid, dimethoate, malathion-methoxychlor, and endosulfan would replace carbaryl. One application of any of the alternatives would replace one application of carbaryl, but where carbaryl is applied more than once, one application of imidacloprid or dimethoate would suffice.
Where cutworm is the primary target pest, chlorpyrifos would replace carbaryl. On acres where carbaryl is applied more than once for cutworm control, one application of chlorpyrifos would suffice.
No change would occur in yield or quality where any of the alternatives are used. The continued wide use of carbaryl on Washington and Idaho wine grapes when more effective and economical alternatives are available is mainly due to grower convention. The overall cost (replacement compounds) of replacing carbaryl with imidacloprid, dimethoate, malathion-methoxychlor, endosulfan, and chlorpyrifos would be $66,000 ($27 per base acre). See also Table 5.
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