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S.J. McArtney and J.D. Obermiller

A series of experiments was undertaken to compare the performance of an axial fan air blast sprayer equipped with air induction (AI) or conventional (C) nozzles in medium density apple (Malus ×domestica) orchards. Performance was compared by assessing 1) spray coverage within the canopy at four levels of across-row wind speeds, 2) ground deposits from airborne drift under still conditions, and 3) biological efficacy of a postbloom thinning spray and a seasonal “high-risk” fungicide program where thiophanate methyl was not included. Spray coverage was reduced by up to 50% with increasing across-row wind speeds, the most dramatic reductions occurring between 0 and 4 mph and at heights greater than 8 ft in the canopy. AI nozzles resulted in a 2-fold increase in spray coverage in the canopy of trees in the row immediately adjacent to the sprayer compared with C nozzles regardless of across-row wind speed. AI nozzles resulted in significantly less airborne drift compared with C nozzles under still conditions in an open field and within a mature ‘Cripps Pink’/ ‘M.7’ orchard planted in rows 20 ft apart. Sprayer efficiency, measured as the proportion of total spray volume that was intercepted by the tree canopy, was higher for an airblast sprayer fitted with AI nozzles (38%) than for C nozzles (26%). The efficacy of a postbloom thinning spray (100 ppm benzyladenine plus carbaryl at 1 lb/100 gal) applied to ‘Morgan Spur Red Delicious’/‘M.111’ trees planted at a between-row spacing of 15 ft was slightly greater when applied with AI nozzles compared with C nozzles. However, application of a “high-risk” fungicide program with AI nozzles resulted in a higher incidence of fruit with flyspeck (Zygophiala jamaicensis) at harvest compared with C nozzles. These inconsistencies were related to the combined effects of nozzle type, orchard row spacing, and canopy density on spray deposition on trees in the second row from the sprayer or to possible effects of nozzle type on droplet density on the target. AI nozzles should provide equivalent or possibly improved coverage and biological efficacy compared with C nozzles in well-managed orchards planted at distances of 18 ft or less between rows. However, when orchard rows are spaced greater than 18 ft apart, AI nozzles will result in reduced spray coverage and chemical efficacy compared with C nozzles because of a reduction in spray carry-over to adjacent rows as a result of reduced airborne drift.

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S.J. McArtney and D.C. Ferree

Dormant, 2-year-old, own-rooted `Chambourcin' grapevines (Vitis sp.) were subjected to two levels of root pruning (none, two-thirds roots removed) and were subsequently trained with either one or two canes. Vines were destructively harvested at bloom and after harvest when dormant to determine the effect of stored reserves in the root and competition between shoots for these reserves on vine growth and berry development. Removing 78% of the root system reduced shoot elongation and leaf area more effectively than did increasing the number of shoots per vine from one to two. Root pruning reduced the elongation rate of shoots for 45 days after budbreak, whereas increasing the shoot number reduced the shoot elongation rate for only 20 days after budbreak. A positive linear relationship was observed between leaf area per shoot at bloom and the number of berries per single cluster. These results demonstrate the importance of 1) the roots as a source of reserves for the initial development of vegetative tissues in spring, and 2) the rapid development of leaf area on an individual shoot for high set of grape berries on that shoot.

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D.C. Ferree, S.J. McArtney and D.M. Scurlock

Vines of container grown `DeChaunac', `Vidal blanc', `Seyval blanc' and `Chambourcin' grapes were subjected to 5 days of 80% shade at prebloom, bloom or 2 and 4 weeks after bloom. Fruit set, cluster weight, berries per cluster and juice components [soluble solids concentration (SSC), pH and titratable acidity] of `DeChaunac' and `Vidal blanc' were not affected by a short period of intensive shade. `Chambourcin' was sensitive to a shade period near the time of bloom for most of the aforementioned factors, while `Seyval blanc' was intermediate in sensitivity. Shot (green, hard, and undersized) berries of `Chambourcin' and `Seyval blanc' were increased by a 5-day period of shade 2 or 4 weeks after bloom. In a second study, container-grown `Chambourcin' on 3309C (V. riparia × V. rupestris) with one or two clusters and `Vidal blanc' with one cluster were subjected to the following light regimes beginning at bloom for 5 weeks: supplemental light, ambient greenhouse light and 30%, 50% or 80% shade. Yield, fruit set, specific leaf weight (leaf dry weight/leaf area), saturation index, and total leaf chlorophyll increased linearly with increasing irradiance. `Chambourcin' juice pH, SSC, leaf chlorophyll a/b ratio, cluster color development and hue angle decreased as irradiance increased, likely related to crop reduction. Responses in `Vidal blanc' followed similar trends, but differences were not as great. Results demonstrate that light is an important determining factor in fruit set of French-American hybrid grapes and fruit set of some cultivars are sensitive to short periods of intense shade.

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C.R. Unrath, J.D. Obermiller, A. Green and S.J. McArtney

The variation in natural fruit drop of ‘Scarletspur Delicious’/‘M.7’ (M.7) apple (Malus ×domestica) trees in a commercial orchard over a period of 11 consecutive years was visualized using box and whisker plots. Delaying harvest until 1 week after the normal harvest date resulted in fruit drop ranging from 2% to 33% depending on the year. The effects of aminoethoxyvinlyglycine (AVG) and naphthaleneacetic acid (NAA) on fruit drop and fruit firmness at normal and delayed harvests was monitored each year. AVG and NAA programs tended to mitigate fruit drop most effectively in years when natural fruit drop was heavy. AVG delayed the loss of fruit firmness, whereas a preload NAA program delayed firmness loss in fruit that were harvested 3 weeks after the normal harvest date only. A standard NAA program for drop control did not accelerate softening of ‘Scarletspur Delicious’ during the first 3 weeks after the normal harvest date. Growers should closely monitor fruit maturity and stem loosening during the harvest window each year to minimize the risk of major losses due to fruit drop. When timely harvest is not possible, perhaps due to unforeseen weather events or constraints in labor availability, or poor management, then use of harvest management aids such as AVG or NAA becomes critical on cultivars prone to fruit drop.

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H.N. De Silva, D.S. Tustin, W.M. Cashmore, C.J. Stanley, G. Lupton and S.J. McArtney

A number of mass—diameter equations were compared for their potential use in indirect measurement of fruit masses of `Royal Gala' apple (Malus ×domestica). The fruit fresh-mass—diameter relationship changed with time during the season, hence no single function fitted the data well. Smooth piecewise functions that assume different relationships for intervening segments of a curve bounded by knots on the x-axis are particularly useful for modeling such data. The curve is said to be smooth because the first derivative of the function is continuous on the interval, including the knots. Two such equations, a three-parameter piecewise power function and a five-parameter spline exponential function, provided good fits to data. For both equations, the estimated mean bias on individual fruit predictions was within 5% of predicted mass over the two validating data sets. As for the precision conditional on no bias, a sample size of 20 fruit gave standard errors within 2.5% of mean predicted mass. These precisions are adequate to meet the industry requirements for monitoring fruit mass through the growing season. There was evidence of a seasonal difference in the estimated bias, but we were unable to confirm that this variation resulted from seasonal differences in fruit shape. Application of these two equations to data from other regions suggested that divergence from the estimated functional form may in fact be greater under increasingly different climatic conditions. Hence, further investigations to identify possible sources of these differences are necessary before the proposed equations can be applied across climatically different regions.