Influence of Planting Date and Planting Distance on Population Density of Onion Armyworm

Onion is an important crop in the province of Nueva Ecija, Philippines. Currently, its productionis being constrained by onion armyworm (OAW; Spodoptera exigua). The impact of plantingdates and distance on the infestation of OAW was studied across two productions. The aim isto evaluate the influence of different combinations of planting dates (November, December, andJanuary) and row spacing [5 cm x 10 cm, 8 cm x 10 cm, 10 cm x 10 cm, and farmer’s practiceor waray (6–10 cm x 6–10 cm)] on the damage and population density of OAW. The count ofobserved OAW larvae from the earliest month (November) and during the month of the usualproduction period (November–December) was negligible to minimal. However, a significantincrease in the OAW population during late planting (January). In terms of leaf damage causedby the OAW feeding, November, December, and January planting had an increasing percentageas the OAW population also increased. There was an increase in bulb diameter as the row spacingwidens (10 cm x 10 cm), as well as an increase in the number of marketable bulb onions whenit is narrow (5 cm x 10 cm). This study showed that planting dates and distances should be oneof the major considerations in onion production and insect pest management.