Growth Conditions, Crop Load and Fruit Size Affect Sheepnosing in Grapefruit

We evaluated crop load, fruit yield and size in several grapefruit blocks on the central Florida Ridge and in the Indian River areas over three growing seasons to determine potential causes of elongated, sheepnosed grapefruit. Previous studies showed that relatively higher rates of N fertilization and high early season (February-July) temperatures within tree canopies resulted in high percentages of sheep nosed fruit. Grapefruit trees on the Ridge generally had much lower percentages of sheepnosed fruit than in the Indian River area. Fruit shape became more sheepnosed between early and late harvests in all Indian River blocks evaluated, but not in most central Ridge blocks. Many factors including fruit variety, rootstock and crop removal that lowered yields or increased average fruit size, also increased the percentage of sheepnosed fruit. Doubling the potassium fertilizer rate in the spring time, tended to increase yield, decrease average fruit size, and decrease sheepnosing. Withholding all irrigation in a white grapefruit block in the Indian River area decreased fruit size and percentage of sheepnosed fruit. Overall, comparable trees with lower crop loads and larger fruit had more sheepnosed fruit than trees with higher crop loads and/or smaller fruit. These studies underscore the importance of crop load and fruit growth potential in determining sheepnosing in grapefruit. Many factors determine the percentage of grapefruit that can be shipped to fresh markets and thus, the net return to growers and packers. Misshapen, sheepnosed fruit is consistently among the top five causes of fruit elimination at the packinghouse (Miller and Burns, 1992; Ritenour et al., 2003). Sheep nosing, or stem-end taper, is often associated with thick, puffy, or coarse rinds of relatively large fruit (Soost et aI., 1965). There is much confusion in the literature about causes of sheep nosing which are not fully understood (Sauls, 1998). High rates of N fertilization can lead to more sheep nosing in Materials and Methods Experiments were conducted using mature grapefruit (Citrus paradisi Macf.) trees growing on the CR near Lake Alfred or in the IR area from 2003 to 2005. Trees on the CR were growing in well drained Candler sand whereas IR trees were growing in several types of sandy soils all requiring bedding to ensure good drainage. All trees received normal horticultural care including irrigation, fertilizer, and pest control except where noted as part of the experimental treatments. Experiment 1. Grapefruit cultivars, canopy position and cover treatments. A CR block of 16-year-old 'Marsh Seedless', 'Ruby *Corresponding author; e-mail; [email protected] This research was partially supported by the FOOC and the FL Ag Exp. Stn Journal Series No R-IO970 9R Prnr li1n .~tntp llrnt .~nr , R. 900~