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.
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.
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.
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.
David R. Ouellette, C.R. Unrath and Eric Young
One-year-old unbranched `Empire' apple (Malus domestica Borkh.) trees on Malling 26 EMLA and Malling–Merton 111 EMLA rootstocks were planted in Nov. 1991 or Mar. 1992 at an eastern Piedmont or mountain site of North Carolina. In Mar. 1992 and 1993, trees were dormant-headed and then subjected to one of five branch-inducing techniques: 1) control—untouched, 2) notching—removing a thin band of bark above each lateral bud, 3) leaf removal—periodic removal of immature apical leaves, 4) bending—placing at horizontal and setting upright in summer, or 5) renewal—setting a lateral branch upright as the new leader. The second year (1993), half of the trees were periodically sprayed with Promalin (GA4+7 + BA). At the Piedmont site, notching, leaf removal, and bending resulted in more branching than the control after 1 year. At the mountain site, leaf removal was considerably less effective in inducing branches. Bending produced asymmetric trees and, at the mountain site, considerably reduced terminal shoot growth. Planting date had little influence on branching. Two years after planting, notched trees were significantly larger and had twice as many branches as other trees. Promalin increased branching on current-season growth and, when combined with leaf removal, resulted in the most uniform distribution of branches along the length of the central leader. Using notching or Promalin produced a tree structure suitable for high-density plantings. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA), gibberellins A4 + A7 (GA4+7).
Ali M. El-Khoreiby, C.R. Unrath and L.J. Lehman
A single foliar spray of 250 mg paclobutrazol/liter was applied to 7-year-old `Oregon Spur Delicious' (OSD) or `Smoothee Golden Delicious' (SGD) apple trees (Malus domestica Borkh.) at 12 growth stages between tight cluster and petal fall plus 28 days. A linear increase in fruit length and length: diameter ratio and a linear decrease in percent soluble solids content were observed on OSD as sprays were applied later in the season. Russet formation on SGD was excessive if treatment was made between early bloom and petal fall. For both cultivars, best control of shoot growth and minimal change in fruit characteristics occurred when paclobutrazol was applied after bloom. Chemical name used: β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Laura J. Lehman, C.R. Unrath and Eric Young
Mature spur-type `Delicious'/seedling apple trees (Malus domestica Borkh.) were examined for 2 years after paclobutrazol (PB) foliar sprays with or without a soil cover to direct spray runoff away from the root zone, soil sprays, or a trunk drench. Foliar sprays with runoff reduced shoot number and fruit pedicel length in the year of treatment, but had no effect on shoot length. Trees that received foliar sprays with no runoff had fewer and shorter shoots and shorter pedicels the year after treatment. Soil sprays or a trunk drench reduced shoot number and pedicel length for 2 years after application, while only soil sprays reduced fruit weight, diameter, and length. Chemical name used: β- [(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1 H -1,2,4,-triazol-1-ethanol (paclobutrazol).
Laura J. Lehman, Eric Young and C.R. Unrath
Spur-type or nonspur `Delicious' apple scions on either Malus domestica Borkh. (seedling) or M.26 rootstocks received paclobutrazol foliar sprays in one or two `consecutive years or a soil drench in the year of planting. For each scion, total shoot, root shank, and tree dry weights measured in the 3rd year after planting were suppressed by all treatments. Trees on M.26 put less dry weight into rootstock wood after foliar sprays, but trees on seedling were not similarly affected. No treatment influenced fibrous root dry weight of the spur-type scion on seedling, while all treatments suppressed dry-weight gain of the same scion on M.26. All trees had higher root: shoot ratios and blossom densities 3 years after the soil drench and several had higher ratios after foliar sprays. Chemical name used: ß-[(4-chlorophenyl)methyl] (l,l-dimethylethyl)-l-H-1,2,4-triazole-l-ethanol (paclobutrazol, PB).