Growth conditions affect sheepnosing in grapefruit

James P. Syvertsen, L. Gene Albrigo, Mark A. Ritenour, Jill M. Dunlop, Arnold W. Schumann, Richard C. Vachon, Robert R. Pelosi, Michael S. Burton

Abstract


Tree growth and/or environmental conditions that cause grapefruit (Citrus paradisi Macf.) to develop an abnormally elongated, sheepnosed shape are not well understood. We manipulated early season fruit growth by modifying tree canopy temperature in grapefruit blocks in the Central Ridge and Indian River regions of Florida to determine growth effects on fruit shape. Elevating early season temperature in tree canopies by placing clear plastic tents over trees from before bloom (February) until July, increased the percentage of sheepnosed fruit above that of the uncovered control trees both areas and in four different grapefruit cultivars. Covering trees over the same period with 50% shade cloth tended to reduce the percentage of sheepnosed fruit. Overall, fruit became flatter as the season progressed but in the Indian River area, sheepnosing tended to increase between October and January. On the Ridge, there were no differences in the percentage of sheepnosed fruit among the different grapefruit cultivars. In another experiment on the Ridge evaluating the effect of nitrogen (N) fertilizer rate on fruit shape, 'Ruby Red' trees previously fertilized with 250 lb N/acre per year had more sheepnosed fruit (14%) than trees that received 100 lb N/acre per year (3%). If we can understand the interactions between determinants of fruit growth, fruit size, and fruit shape, we should be able to minimize sheepnosing problems and increase packout.

Keywords


citrus paradisi; canopy temperature; fertilizer n rate; fruit height/width ratio

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