No. 24 Article 4/November 5, 2004

Review of 2004 Soybean Insect Management Trials

The management of insects in soybeans has not always been as prominent as it has been over the past few years. With the introduction of the soybean aphid and increasing presence of bean leaf beetles in Illinois, soybean insect management is becoming ever more important. The increased awareness of insects in soybeans has led to a higher incidence of insecticide use and a concern of unnecessary pesticide applications (see "Insects Infesting Soybeans? Or Not?" in issue no. 18 of the Bulletin, July 23, 2004). Also, the likelihood of the registration of insecticidal seed treatments on soybeans in Illinois may lead to their widespread use. Due in part to these factors, we investigated the benefits of different pesticide treatment combinations, insect levels, and their effect on yield in three soybean trials this summer. These trials were conducted as part of our Insect Management Program and were funded by the Illinois Soybean Program Operating Board and Syngenta Crop Protection.

Two soybean trials were established this year, targeting the management of the bean leaf beetle. The objective of this trial was to determine the most timely, practical, and economic approach for managing bean leaf beetles, with the potential for reducing the incidence of soybean diseases, such as bean pod mottle virus.

The two bean leaf beetle trials were established in Whiteside and Stephenson counties on May 4 and 5, respectively. The trials were established in areas where the presence of bean leaf beetles early in the growing season, and possibly throughout the growing season, was optimized (i.e., the plots were planted in fields bordering wooded areas and alfalfa fields). Densities of bean leaf beetles in the areas where the trials were established and throughout Illinois were quite low throughout 2004. No economically threatening densities of bean leaf beetles were observed in any of the treatment plots at any time. However, the trials were sampled throughout the growing season, numbers of all insects were recorded, and plots were harvested to determine potential yield differences.

Treatments in the two bean leaf beetle trials are as follows:

1. Cruiser seed treatment

2. Cruiser seed treatment + a foliar application of Warrior to control first-generation beetles (July)

3. Gaucho seed treatment

4. Gaucho seed treatment + a foliar application of Warrior to control first-generation beetles (July)

5. A foliar application of Lorsban 4E to control overwintering beetles (May) + a foliar application of Lorsban 4E to control first-generation beetles (July)

6. A foliar application of Mustang Max to control overwintering beetles (May) + a foliar application of Mustang Max to control first-generation beetles (July)

7. A foliar application of Warrior to control overwintering beetles (May) + a foliar application of Warrior to control first-generation beetles (July)

8. A foliar application of Warrior to control first-generation beetles (July)

9. Untreated check

A third trial was established in Ken-dall County targeting control insect pests in soybeans. The trial was planted late (in June) purposely to enhance the likelihood of development of economically threatening densities of soybean aphids. The treatments in the trial include various combinations of fungicidal seed treatments, insecticidal seed treatments, foliar-applied fungicides, and foliar-applied insecticides. The trial was established in an area in which infestations of soybean aphids had been relatively common, and occasionally significant, since 2000. As with our other two soybean trials, no economically threatening densities of soybean aphids, or any other insect pest, developed at this location. However, all plots were sampled for insects, and the plots were harvested to determine potential yield differences.

Data from all three of these trials are currently being analyzed. The results will be presented in an upcoming issue of the Bulletin. We hope to give more insight into the possible yield increase with the use of systemic nicotinoid seed treatments or application of insecticide + fungicide, even in the absence of economically threatening insect levels.--Kelly Cook, Ron Estes, and Kevin Steffey

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