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F.R. Harker, J.H. Maindonald, and P.J. Jackson

Flesh firmness is a characteristic used to indicate fruit quality. Experimental design and data analysis are important when comparing devices that measure fruit firmness. We compared the Effegi penetrometer operated by hand, mounted in a drill press and then operated by hand, and mounted on a motorized drive and operated remotely; the hand-operated EPT pressure tester; the Instron with an Effegi probe; and a hand-operated prototype of the twist tester. Devices varied in operator differences and precision. Comparisons between devices were at the within-fruit level of variability and, therefore, more precise than comparisons where different device-operators used different fruit. We demonstrate statistical methods that are appropriate for making the comparisons of interest and discuss the possible cause of differences between operators and between devices. We also discuss how the mechanical properties of the devices may affect results and consider implications for their practical use. In this study, we found the precision of discrimination between soft and hard apples was best using the Instron in 1992, while the Instron and hand-held Effegi penetrometer were comparable in 1991. For kiwifruit, the hand-held Effegi penetrometer consistently gave the most precise measurements of softening in 1991, while the twist test was the most precise in 1992.

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Jeffrey P. Mitchell*, Gene M. Miyao, Jim J. Jackson, Lee F. Jackson, Tom Lanini, Charlie G. Summers, and Jim J. Stapleton

Two field comparisons of conservation tillage tomato production alternatives following wheat were conducted in California's Central Valley. Both studies compared: 1) standard tillage; 2) bed disk or permanent bed minimum tillage; and 3) strip-tillage following winter wheat crops that were harvested the previous June. Processing tomatoes were produced at the site in Davis, Calif., and fresh market tomatoes were grown in Parlier, Calif. At both sites, establishing tomatoes using a commercial transplanter or a modified conservation tillage transplanter achieved adequate stands even in the minimally-tilled strip-till system. Timing of the strip till operation, however, is critical so that large chuncks of dry soil are not brought up and so that these do not create very rough bed surfaces that may cause harvest problems, particularly for processing tomatoes. Machine harvesting the crop at the Davis site did not seem to create any mechanical difficulties or generate additional trash going into the harvest trailer. This may have been due to the fact that by harvest time, the majority of the surface residue from the previous wheat crop had already been broken down or at least sufficiently worked into the soil to pose minimal mechanical harvester impedance or contamination. Tomato yields for the reduced till systems equalled yields of the standard till systems at both sites.

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S.J. Kays, W.J. McLaurin, Y. Wang, P.D. Dukes, J. Thies, J.R. Bohac, and D.M. Jackson

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Cody J. Stewart, S. Christopher Marble, Brian Jackson, Brian J. Pearson, P. Christopher Wilson, and Dwight K. Lauer

The objective of these experiments was to determine if preemergence herbicides perform similarly across pine bark that was aged for varying lengths of time including 0, 4, 8, and 12 months after bark removal from harvested trees. Three preemergence herbicides were evaluated for three separate weed species, including 1) Cardamine flexuosa With. (bittercress) with isoxaben, 2) Digitaria sanguinalis (L.) Scop. (large crabgrass) with prodiamine, and 3) Oxalis stricta L. (woodsorrel) with dimethenamid-P. Leaching of herbicides through substrates was evaluated for prodiamine. Weed growth in the various substrates was variable, but few differences were detected in weed growth among the pine bark substrates evaluated. For isoxaben and prodiamine, weed control was similar among the pine bark substrates in most cases when label rates were applied. Although some differences were detected in prodiamine performance across different pine bark ages, a high level of control was achieved in all cases at rates well below manufacturer recommendations. Prodiamine leaching was minimal in all substrates. It would be recommended that growers test substrates for physical properties before use so that irrigation and other production inputs could be modified if needed. In most cases, growers should expect similar performance of preemergence herbicides regardless of pine bark substrate age.

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J.R. Bohac, P.D. Dukes Sr., J.D. Mueller, H.F. Harrison, J.K. Peterson, J.M. Schalk, D.M. Jackson, and J. Lawrence