Jim E. Wyatt, Emily W. Gatch, and Craig H. Canaday

Data on zucchini squash fruiting stem length, stem cross sectional area, force needed to shear the stem and force required to break the stem from the plant, along with several correlations among these characters, indicate that ‘Lynx’, ‘Jaguar’, and ‘Cashflow’ are relatively good candidates for mechanical harvest.

Mechanical once-over, destructive harvest of yellow summer squash is feasible to do, considering the ease of removal of the fruit from the plant by the harvester. Zucchini fruit, however, are much harder to remove, due mainly to the inherent difference in structural anatomy of the stem attachment of the fruit (botanically the peduncle). Zucchini-type fruit generally have a shorter, thicker stem and do not break easily, compared to yellow types. Frequently, when a zucchini fruit is held at the blossom end and twisted, the breaking point will be the squash itself, rather than the stem.

The objective of this study was to compare several zucchini-type hybrids to determine if differences exist in the stem anatomy/morphology which would make mechanical harvest more efficient.

Plots were prepared in the fall of 2002 by broadcasting 600 lbs per acre of 15-15-15, disking, and preparing the seedbed by smoothing with a springtooth harrow followed by a rolling basket. Individual plots were 40 feet long and consisted of two rows spaced 2.5 feet apart. Plant spacing within the row was approximately 2 feet. Six zucchini hybrids were planted in a randomized complete block design with four replications. Ethalfluralin (Curbit®) herbicide was applied at 3 pints per acre and watered in after planting. Supplemental water was provided by overhead irrigation as needed.

Fruit were harvested when diameter was 1.50 to 2.25 inches by cutting the stem adjacent to the main stalk of the plant. The following measurements were made on individual fruit: 1) diameter, 2) weight, 3) stem cross sectional area, and 4) stem length. Stem cross sectional area was measured by cutting the stem in half crosswise in the center, blotting the moisture from the cut surface, inking the surface on an ink pad, making an imprint on paper, and measuring the area with an leaf area meter.

Another study involved measurement of the force required to remove the fruit from the plant. Random fruit 1.50 to 2.25 inches in diameter were selected. The hook of a battery operated digital hanging scale (Cardinal Scale Manufacturing Co., Webb City, Mo) was placed under the squash stem and, while holding the fruit, uniform upward pressure was applied until the stem was severed from the plant. Five fruit from each plot were measured.

Data were analyzed by analysis of variance using appropriate SAS (SAS Institute, Inc., Cary, NC) procedures. Mean separation was by Duncan multiple range test.

Correlations were made between fruit diameter:stem length, fruit diameter:stem cross-section area, fruit weight:stem length: fruit weight:stem cross-section area, stem length:stem cross-section area, fruit diameter:stem shear force, fruit weight:stem shear force, stem length:stem shear force, fruit diameter:pull force, and fruit weight:pull force.

Significant differences were found among squash hybrids for all stem measurements which were made (Table 1). Theoretically, the hybrid with the longest stem, the smallest stem cross sectional area, and the lowest shear force and pull force should be best suited for mechanical harvest. ‘Lynx’ fits these criteria with stem length not significantly different from ‘Spineless Beauty’, a stem cross sectional area significantly smaller than any other hybrid, and shear and pull forces not significantly different from ‘Cashflow’. ‘Cashflow’ would also be a good candidate, since it differs in ranking from ‘Lynx’ only in stem cross sectional area. On the other hand, ‘Tigress’ has the shortest stem, one of the largest cross sectional areas, and the highest stem pull force in the test which may indicate more difficulty in removing fruit from plants of this hybrid.

Correlations of fruit and stem characteristics give several indications of possible advantages that some zucchini hybrids may have over others for mechanical harvest (Table 2). ‘Jaguar’ stem length increases with increasing fruit diameter and weight; however, stem area cross section significantly decreases with fruit diameter and has a slight negative correlation with fruit weight. This indicates that stems of this hybrid get longer but thinner as fruit develop, theoretically making mechanical removal of the fruit from the plant easier. This advantage may be offset, however, by a significant increase in stem shear force as fruit mature.

All of the hybrids tested except ‘Tigress’ have highly significant correlations between stem length and stem cross sectional area (Table 2). The stems of ‘Tigress’ may be short and thick from the time of flowering and maintain the same relative size as they mature.

‘Cashflow’ has the lowest pull force in the study (Table 1) but has a significant correlation of pull force with fruit diameter and weight. This would indicate that very immature fruit (1.5 to 1.8 inches) would be very easy to detatch from the plant using a mechanical harvester.

Table 1. Characteristics of zucchini squash stems which could affect the efficiency of mechanical removal of fruit from the plant.

*, **, and ***=0.05, 0.01, and 0.001 levels of probability

Table 2 (continued)

*, **, and ***=0.05, 0.01, and 0.001 levels of probability

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Copyright © 1999 by The University of Tennessee. All rights reserved.

This research represents one season's data and does not constitute recommendations.  After sufficient data is collected over the appropriate number of seasons, final recommendations will be made through research and extension publications.