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  • Author or Editor: C. R. Unrath x
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The use of Sevin XLR Plus in chemical thinning applications at or shortly after petal fall in 1998 resulted in serious negative fruit quality effect, especially on `Red Delicious'. This negative fruit quality impact was worse in certain Henderson Co., N.C., orchards. Fruit diameter was reduced by 9%, fruit weight was reduced by 22%, misshapen fruit increased by 30%, eliminator fruit (<2.25″) increased by 102%, severely stunted fruit (<2.0″) increased by 317%. Surface russetting increased by 160% and seed numbers per fruit dropped by 27%. These are “never before seen” fruit quality problems for North Caronlina, which appear to be related to the unusual environmental conditions between full bloom and fruit thinning. Comparing the 30-year weather records, Apr. 1998 was the wettest April on record with twice the average rainfall. There were only two rain free days between bloom and petal fall, and only 9 of the 30 days following bloom were rain-free. Daily lows were at or above while daily highs were below the 30-year average, resulting in an extremely small daily temperature fluctuation. The departure from normal for average daily temperature was highly negative from partial petal fall until 2 weeks post petal fall. Daily relative humidity values for daily minimum, average and maximum were consistently and substantially above 30-year average values. It appears that these environmental extremes with Sevin XLR Plus use has an impact on fruit quality. In one `Golden Delicious' orchard where Sevin formulations could be compared side by side, fruit russetting jumped from 5.3% with 50 WP to 36.2% with the XLR Plus formulation.

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Handgun applications on bearing spur `Red Delicious' evaluated both timing and concentration. At season's end, single 250-ppm applications at petal fall (PF), PF+7, +14 or +21 days reduced growth by 47% to 67%. Concentration of 125, 250, and 375 ppm @ PF+7 were all effective (45% to 55% reduction). Number of pruning cuts, pruning weight, and pruning time were all reduced. Applications at PF+0, +7 and +14 days increased fruit set, and, as a result, fruit weight trended lower. Airblast applications to `Top Red Delicious' applied at PF+3 weeks using 125, 250, and 500 ppm showed good initial growth suppression, but considerable regrowth in August and September. Yet, pruning weight and tree row volume were reduced with no fruit set or quality differences. Multiple, low-rate applications starting at PF on `Granny Smith' were very effective (60-70% reduction). Total application concentrations of 250 ppm were more effective than 500 ppm. The earlier the application sequence was started, the better the growth suppression. Two years of successive 200-ppm applications to the same trees in five separate plots involving three varieties showed an average 32% reduction in year 1 and a 56% reduction in year 2.

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The canopy of an apple orchard can be objectively quantified by using tree height and cross row limb spread to calculate the tree row volume (TRV). Use of the appropriate water rate, adjusted for canopy density, is an effective tool for determining full dilute water rate for airblast applications. To save run off most dilute pesticides are applied at 70% of TRV. TRV model use will be discussed and illustrated. Comparison of handgun vs airblast applications showed more deposition and thinner activity w/handgun. Thinners applied at a fixed concentration of a.i. showed decreased activity as volume decreased. Applications at the same a.i./ha, regardless of water volume showed similar activity at and below TRV water and reduced activity at higher than TRV water, indicating activity loss from run off. Added testing showed uniform thinner activity only if water volume was within ± 20% of tree TRV rate. A fruit dip experiment showed greatly differing natural fruit drop but similar added chemical induced fruit drop between top, lower outside and lower inside of apple trees, a factor which must be adjusted for w/nozzle distribution on large trees.

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Abstract

Under the relatively dry and hot conditions which prevailed in 1972, both evaporative cooling and (2-chloroethyl)phosphonic acid (ethephon) improved fruit color and accelerated fruit maturity. The ethephon-evaporative cooling interaction on color and maturity was far superior to either one alone. Combined cooling-ethephon treatment resulted in 77% crop removal the first week of the season vs. only 5% in the control plot. Evaporative cooling also eliminated the leaf phytotoxicity of 2-(2,4,5-trichlorophenoxy)propionic acid (fenoprop), which was observed under heat stress conditions. In a drier production area, ethephon advanced maturity but did not increase red color. In an adjoining orchard ethephon applied after a 5 cm (2 inch) soil irrigation resulted in an additional 31% of the fruit surface showing red color within 10 days after application.

Open Access
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Abstract

Ethephon [(2-chloroethyl) phosphonic acid] at 250 ppm + 20 ppm of fenoprop [2-(2,4,5-trichlorophenoxy) propionic acid] was applied to fruit only as a dip, to leaves only as a spray, and to fruit and leaves as a normal dilute spray. Fruit color was stimulated only when ethephon was applied to the fruit surface and a direct relationship existed between coverage and color response. A small increase in fruit soluble solids appeared following all applications, while fruit softening occurred only when materials were applied to both fruit and leaves. This softening response is apparently a combined ethephon-fenoprop response. These data imply that ethephon applications should be applied as a dilute spray, using sufficient water to cover all fruit on the tree as thoroughly as possible if maximum color response is to be achieved.

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Abstract

Apple trees treated with (2-chloroethyl) phosphonic ethephon applications at 400 ppm, plus 2-(2,4,5-trichlorophenoxypropionic acid (fenoprop) at 10 ppm for abscission control, approx 1 month before optimum maturity exhibited increased fruit coloration. On some cultivars, fruit firmness, soluble solids, acidity, and soluble solids-acid ratio were altered. Ethephon accelerated red color development of ‘Starkrimson Delicious’ apples whether or not the trees had been previously treated with succinic acidb-2,2-dimethylhydrazide (SADH); however, the amount of coloration was greater when both SADH and ethephon were used. Ethephon reduced the titratable acidity of ‘Starkrimson Delicious’ fruit resulting in a greater soluble solids-acid ratio. ‘Golden Delicious’ fruit exhibited a definite yellowing of skin color when treated with ethephon but flesh softening was excessive at higher concn. Ethephon treatments applied without an accompanying abscission control chemical resulted in fruit abscission within 2 to 7 days depending on concn. SADH treatment delayed abscission 2 to 3 days as compared to no SADH treatment, where no abscission control was used. Fenoprop was superior to naphthalene acetic acid (NAA) in reversing the abscission stimulation of ethephon.

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High-density apple (Malus domestica) orchard management techniques and productivity were evaluated on an old orchard replant site in North Carolina. Trees were planted at 5 × 10 ft (1.5 × 3.0 m), giving a tree density of 871 trees/acre (2152 trees/ha). Well-branched `Smoothee Golden Delicious' trees on `Mark' rootstock were planted in 1990. Orchard-management factors which increased cumulative yield were supplemental irrigation (+21%), slender spindle training (+19%), preplant tree-hole fumigation (+11%), and fumigation + postplant mefenoxam (Ridomil) collar drench (+17%). Collectively, these factors increased cumulative yield by 55%. Supplemental irrigation was the only treatment to significantly impact fruit quality, increasing average fruit size by 20% over the 11-year study.

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Abstract

Low vol overtree sprinkler irrigation was used on ‘Starkrimson Red Delicious’ apples during 2 successive growing seasons to determine the potential for moderating environmental extremes and reducing moisture stress through evaporative cooling. Irrigation, applied when air temp exceeded 87°F, substantially cooled plant tissues. In addition a residual cooling effect from evaporation of irrigation water following application was evident. The fruit exhibited the greatest amount of cooling (avg of 12.1° and 8.1°F in 1969 and 1970, respectively) because evaporation cooling negated radiation heating which normally caused fruit temp to be well above air temp. Cooling effects were proportional to length of operation of the irrigation system.

Open Access