Integrated Crop Management

Gaucho for soybean approved

The Environmental Protection Agency (EPA) has issued a notice of a Section 18 Crisis Exemption for Gaucho 480 Flowable in Iowa beginning March 28, 2003, and continuing as permitted by EPA under the specific exemption request not to exceed 1 year. Gaucho is known by the common name imidacloprid. It is approved for use on soybean seed for soybean grown for seed and identity preserved food grade soybean. This product will only be used as a seed treatment. The method of application is a seed treatment and seed will be treated at seed processing plants before packaging seed for distribution. The rate of application is 2 fluid ounces of Gaucho 480 Flowable per hundredweight of seed or 1 fluid ounce of Gaucho 480 per seed unit. A seed unit is 50 pounds and the normal planting rate is 1.3 seed units per acre. There is no preharvest interval.

The following reasons were given by the EPA as to why the Section 18 was granted. Bean leaf beetles are a vector of bean pod mottle virus. As a result of bean leaf beetle feeding on soybean plants and the spread of bean pod mottle virus, growers have experienced reduced yields and poor-quality seed or grain. Some producers reported up to 100 percent infection with bean pod mottle virus and losses due to reduced yield and poor-quality seed. Food-grade soybean producers have lost a major portion of their export markets because of stained and wrinkled soybean seed due to bean pod mottle virus. A Section 18 Crisis Exemption is being authorized considering that there is insufficient time to wait for EPA's approval of the Specific Exemption because seed treatments need to be started now, considering soybean seed will have to be shipped to the grower in the next 2 to 3 weeks.

Gaucho is expected to provide early-season protection against bean leaf beetles, which can transmit bean pod mottle virus. Gaucho will not control the virus. The table shows data from last year on the performance of several insecticides for bean leaf beetle control. Gaucho, dimethoate, and Warrior are all approved for use in soybean; Cruiser is not labeled for use in soybean.

Bean leaf beetle densities in soybean treated with seed treatments (Cruisera or Gaucho) or liquid insecticides (dimethoate or Warrior), Gilbert, IA, 2002. Iowa State University.

Bean leaf beetles/3 row ft
Treatment Rateb May 16 May 23 May 31 June 5 June 12 June 20
Cruiser 20 g 2.0 0.3 5.7 5.3 4.7 1.7
Cruiser 30 g 0.0 0.3 6.3 7.3 3.3 2.3
Cruiser 50 g 0.3 0.0 4.0 4.3 2.3 1.0
Cruiser 100 g 0.0 0.7 1.7 3.3 1.7 0.7
Gaucho 62.5 g 0.7 0.0 7.7 7.7 4.0 1.3
Warriorc 3.2 oz 9.7 0.7 5.3 5.3 3.7 2.7
Dimethoated 8 oz 14.0 25.7 0.7 2.7 3.0 1.7
Cruiser + Warriord 30 g + 1.92 oz 0.3 0.3 4.7 0.3 2.3 1.7
Check --- 3.0 18.7 3.0 6.7 4.3 2.0
P = 0.05e LSD = 6.5 LSD = 9.2 n.s. LSD = 2.7 n.s. n.s.

a Cruiser is not labeled for use in soybean.

b Planted April 30; Cruiser and Gaucho rates at stated grams a.i./100 kg seed.

c Warrior @ 3.2 oz a.i./acre applied May 17.

d Dimethoate @ 8 oz a.i./acre and Warrior @ 1.92 oz a.i./acre applied May 29.

e n.s., no significant differences between treatments.

This article originally appeared on pages 33-34 of the IC-490 (4) -- April 14, 2003 issue.

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