The effect of increasing rates of fertilizer on insect pests of organically grown squash ‘Gentry’ (Cucurbita pepo l.)

Abstract

Organic producers typically apply 100% of their nitrogen (N) requirements as dry granular fertilizer in the bed prior to establishment of plastic mulch and drip irrigation due to the high costs of liquid fertilizer. Insects, particularly those that feed in the phloem, may reach higher levels when there is excess N available. This study examined the effects of three rates of an organic-compliant blended fertilizer on yield and insect pests of yellow crookneck squash, ‘Gentry’ (Cucurbita pepo L.) to determine if increased N rates were associated with greater insect abundance and fruit damage. The design was a complete factorial arranged in an RCBD with three rates of fertilizer N: 84; 168; and 336 kg·ha-1 (75, 150, and 300 lb/acre) and three insect management treatments: floating row cover; organic-compliant insecticide as needed for aphids, whiteflies, and caterpillar pests; and no insect control. Squash was planted on 38-centimeter (18-inch) centers on 1.5-meter (5-foot) beds on 25 April on transitional organic land at the Suwannee County Agricultural Extension Center in Live Oak, FL. Each plot was surrounded by a 3-meter (10-foot) border parallel to the rows and a 4.6-meter (15-foot) border perpendicular to the rows. Insect counts were completed in situ weekly prior to squash harvest. The use of row covers at planting resulted in fewer whiteflies and aphids overall compared to remaining treatments, but insect density was not related to fertilizer rate. Marketable yield was greatest in the greatest N application rate, 15,724 kg·ha-1 (14,039 lb/acre), relative to the remaining rates of N application (P < 0.001) and yields were comparable to state average yields in conventional systems.