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Abstract

The length of the lag phase following treatment and the persistence of the eventual growth suppression effect of 1.15 g paclobutrazol (PBZ) per tree declined as the area of treated soil surface beneath the tree increased. Treating one side of the tree row was as effective as treating both sides, but immediately adjacent “control” trees were largely unaffected by these soil-surface treatments. In a 2nd experiment, single, or multiple sprays applying the same amount of chemical in total gave equal growth control in the season of application, but residual growth control was slightly superior on trees sprayed four or 10 times. All PBZ treatments advanced anthesis but failed to improve flower number or fruit set. The weight of individual cherries was increased in each of the three years following the soil-surface application of PBZ, but, except for a reduction in soluble solids, fruit quality was unaffected. Foliar sprays of PBZ in 1984 led to larger fruit size in 1985, but fruit coloring was delayed and soluble solids were reduced. A preharvest spray of 20 ppm gibberellic acid (GA₃) substantially enhanced the PBZ effect on fruit size and color but also increased fruit firmness, juice acidity, stem length, and fruit removal force and reduced the incidence and severity of pitting following 2 weeks of cold storage. Chemical names used: β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

Abstract

Thirty-two lots of ‘Golden Delicious’ apples (Malus domestica Borkh.) from 22 British Columbia (B.C.) orchards varied in their susceptibility to injury from a 10-day 14 or 18% CO₂ treatment preceding controlled atmosphere storage. In general, the incidence of injury was much higher than in 25 lots of Washington State ‘Golden Delicious’ treated similarly in a commercial storage. A small improvement in firmness was observed in the B.C. fruit. Within the 32 B.C. lots, susceptibility to CO₂ injury was not related to fruit skin color, size, soluble solids or acidity, the N, K, Mg, Ca, Zn, Fe or B content of the leaves, or N, K, Mn, Mg, Ca or Zn content of the fruits. However, Washington ‘Golden Delicious’ were less green, were lower in N, Mn and Zn and higher in K, Mg and soluble solids than B.C. fruit which may provide a clue to their resistance to CO₂ injury.

Abstract

Deblossomed 8-year-old Malus domestica L. ‘Goldspur Golden Delicious’ trees on seedling rootstock exhibited less extension growth than trees that had carried a crop during either the current year or the previous year. Trees in the “on” year consistently had more extension growth than trees in the “off” year. Fruitful branches of ‘Golden Delicious’ and spur-type ‘Golden Delicious’ generally had more new growth than branches without fruit from the same tree.

Abstract

Fruit set on mature spurs and on 1-year-old wood (lateral bloom) was followed as a step in the development of a chemical thinning protocol for ‘Greensleeves’ apple trees. Initial set (fruit firmly attached 15 days after full bloom) was a reasonable predictor of final set on spurs but not on lateral clusters. High initial set values on lateral clusters reduced final set. Likewise, initial and final set values on either spur or lateral clusters were inversely related following a 1000 ppm carbaryl treatment, although lateral clusters were more readily thinned than spur clusters by carbaryl. Without the carbaryl treatment, final set per cluster was comparable on spur and lateral clusters, and final set on lateral clusters was improved by defruiting alternate clusters on these 1-year-old branch sections 15 days after full bloom.

We propose that return flowering of `Fuji' apple can be improved if sufficient flower clusters are removed during or shortly after bloom. In this study conducted at Corvallis, Ore., we evaluated two synthetic auxins, MCPB-ethyl and the Na salt of NAA, each at 0, 4, 8 and 16 ppm, as blossom cluster thinners. Each auxin treatment was applied alone or with 100 ppm ethephon as a tank mix. Six-year-old `Fuji'/M.26 trees were sprayed at full bloom of the king flowers (≈85% of whole-tree full bloom). A follow-up treatment of Sevin XLR (800 ppm carbaryl) was made at 11-mm fruit diameter to determine if carbaryl's known effectiveness as a fruitlet thinner was influenced by the bloom-time auxin or auxin + ethephon treatments. MCPB-ethyl proved ineffective as a bloom-time thinner, whereas the NAA effect on cluster removal was linear with concentration, 16 ppm NAA completely defruiting 33% of initial flower clusters. On control trees fewer than 12% of flowering clusters failed to set fruit. Ethephon alone defruited 25% of the clusters and NAA+ethephon defruited 51% of clusters. It is notable that the NAA and ethephon + NAA treatments did not reduce fruit set on the remaining clusters, resulting in considerable need for hand-thinning. Carbaryl effectively reduced total crop load by increasing the number of defruited clusters and reducing the incidence of doubles and triples. There was evidence to suggest that its effectiveness was compromised by the bloom-time NAA and/or ethephon sprays.

Three experiments were conducted at two locations, two at Summerland, British Columbia, Canada and one at Corvallis, Ore., to evaluate synthetic auxins (MCPB-ethyl or NAA) and ethephon as blossom thinners for `Fuji' apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.]. These experiments also involved application of carbaryl at 1000 mg·L^-1 in the postbloom period. All blossom thinners were sprayed at 85% full bloom while carbaryl was applied at 11-mm fruit diameter. Within these experiments, MCPB-ethyl at up to 20 mg·L^-1 or NAA at up to 21 mg·L^-1 increased whole flower cluster removal linearly with rate; however, with the Corvallis experiment MCPB-ethyl failed to result in any thinning. Neither auxin treatment consistently reduced fruit set on the remaining clusters, resulting in “clustering”. Bloom-time application of ethephon at 100 mg·L^-1 with NAA further reduced crop load. Carbaryl reduced total crop load by increasing both whole cluster removal and number of sites with a single fruit. Return flowering was not improved by the auxin treatments except where there was very excessive crop reduction. Ethephon or carbaryl promoted return flowering with the carbaryl effect being more pronounced. However, this carbaryl effect was significantly countered by the bloom-time auxin whereas ethephon overcame the negative effects of the auxin treatments. The combined use of ethephon and carbaryl was effective in terms of both crop reduction and return flowering benefits. Chemical names used: 1-naphthyl N-methylcarbamate (carbaryl); 2-chloroethylphosphonic acid (ethephon); ethyl 4-(4-chloro-2-methylphenoxy) butanoate (MCPB-ethyl); and 2-(1-naphthyl) acetic acid (NAA).

Abstract

Wetting ‘Golden Delicious’ apples (Malus domestica Borkh.) by dipping or vacuum infiltration in water for 5 minutes before a 10-day prestorage 18% CO₂ treatment increased (CO₂-associated peel injury. Dipping in 20°C water resulted in more injury than a 6° water dip and vacuum infiltration with 20° water resulted in the most severe injury. A detailed scoring system for external CO₂ injury is described.