Evaluation of action thresholds for chronic rice insect pests in the Philippines: II. Whorl maggot and defoliators

Abstract

Action thresholds as insecticide decision tools were developed and evaluated against chronic vegetative stage insect pests of irrigated transplanted rice in the Philippines: whorl maggot Hydrellia philippina Ferino (Diptera: Ephydridae( and two lepidopterous defoliators, Naranga aenescens Moore and Rivula atimeta (Swinhoe( (Lepidoptera: Noctuidae(. Through an iterative process, new threshold characters and insecticide technologies were evaluated at four sites (categorized as high and low pest density sites( over a 13-year period with the objectives of minimizing insecticide usage and maximizing farmer adoption. Characters were evaluated as to their ability to predict significant pest densities and yield loss. Significant differences occurred between high and low pest density sites among the best characters and monitoring methods for both pests. Earlier-planted fields were used as a forecasting tool, showing best results in the high pest density sites. Overall, most threshold characters performed well but the insecticide response was poor. Insecticide control was better with some threshold characters than others due to better timing. Seedling root soak with isofenphos was more effective than granules or foliar sprays against whorl maggot but required a decision before planting. Foliar sprays were most effective if applied twice (2 and 7 days after transplanting(. The best performing characters for whorl maggot were 1 – 2 eggs/hill for the low pest density sites and 15 – 30% damaged leaves in earlier planted fields in high density sites. The best performing characters for defoliators were 10% damaged leaves monitored in earlier planted fields for high density sites and 10% damaged leaves in low density sites. Carbaryl was the most effective insecticide spray against defoliators that combined performance and relative safety.

Keywords:

• Pest control
• irrigated rice
• insecticides
• decision-making
• yield loss
• planting date
• damage pattern

Acknowledgements

We are highly appreciative of the generous cooperation provided by over 400 farmers in the study sites. Their willingness to become experimenters with the research teams and devote at times a tenth of their rice lands to trials is a testament to their desire to seek improvements in rice production technology. Many locally hired project staff were responsible for conducting the trials and their invaluable contributions are acknowledged. Those assisting in Zaragoza were Catalino Andrion and Rodolfo Gabriel, in Guimba George Romero, in Calauan Mariano Leron, Eduardo Micosa, and Carlos de Castro, and in Koronadal Hector Corpuz, Joseph Siazon, Beatriz Velasco, and Anita Labarinto. Cooperation of the staff in the Central Luzon and Mindanao regions of the Philippine Department of Agriculture is highly appreciated.