Influence of spray volume, ground speed, and a sensor-actuated spray controller on melanose control and fruit marking in fresh Indian River grapefruit

ED Stover, James Salvatore, Peter Mcclure

Abstract


Season-long pest control programs using different sprayer parameters were compared for their effects on fruit blemishes from pests and damage from spray phytotoxicity. Sprays were applied in two mature groves of 'Marsh' grapefruit (Citrus paradisi Macf.) on sour orange (Citrus aurantium L.) rootstock near Ft. Pierce, Florida, using a randomized complete block design with entire tree rows as experimental units. Eight spray applications (five of these included copper) were made during 2001 based on timings and materials recommended for fresh fruit production. Sprays were applied during daylight with a Durand Wayland SuperSpray 500[tm] sprayer with a six ultra-sonic sensor SmartSpray[tm] system. Four sets of spray parameters were maintained season-long and were compared with identical material rates per acre: 1) precision spray (using sensor-actuated controllers) at 125 gal per acre applied at 1.1 miles per hour, 2) standard spray at 125 gal per acre applied at 1.1 miles per hour, 3) standard spray at 250 gal per acre applied at 1.1 miles per hour, and 4) precision spray at 125 gal per acre applied at 2.3 miles per hour. Random samples of interior and exterior fruit were harvested from each of three typical trees in each experimental row and were assessed for melanose and melanose-like marking. On exterior fruit, copper injury superficially similar to melanose was higher at 125 gal per acre than 250 gallons per acre in both groves (one grove significant at p 0.05, the other at p 0.10). In one grove, melanose control on interior fruit was greater at 250 gal per acre than 125 gal per acre when compared at 1.1 miles per hour application speed. In the other grove, with larger trees, melanose control on interior fruit was reduced at the higher ground speed. Use of the precision spray feature reduced pesticide usage without affecting pest control.

Keywords


copper; cupric hydroxide; citrus paradisi; fungicides; pesticides; phytotoxicity; precision sprayer; SmartSpray[tm]; spray runoff

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283