Experiments were carried out in the southeastern United States between 1998 and 2006 to evaluate the potential for applications of NAA, Ethrel, or both, in the on-year of a biennial bearing cycle to increase return bloom in apple. Four bi-weekly applications of 5 ppm NAA beginning in mid June (summer NAA) increased return bloom, measured as the percentage of floral spurs in the year after treatment. The level of return bloom on trees receiving a summer NAA program was more than 2-fold higher than on untreated control trees, averaged across seven different experiments. Four applications of 5 ppm NAA at weekly intervals leading up to harvest (August/September) increased return bloom also. Combining 150 ppm Ethrel with summer NAA sprays resulted in an additive effect on return bloom compared to NAA or Ethrel alone. The effect of flower cluster density on return bloom the following year was more negative on control trees than it was on trees sprayed with Ethrel in the previous year. Treatment effects on fruit maturity at harvest were generally neutral, although flesh firmness was reduced in some experiments. NAA or Ethrel sprays in the on-year of a biennial bearing cycle may provide a strategy for achieving more consistent flowering and cropping in apple.
The relationship between intensity of flowering and various aspects of cropping are reviewed for fruit species. Relatively light flowering can limit yield in most fruit species. This commonly occurs in young trees that have not achieved full production and in “off” years for varieties that display alternate bearing. When trees mature, many species will carry fruit numbers that exceed commercially desired levels, resulting in excessively small fruit and accentuating alternate bearing. The economic disadvantages of excess cropload have resulted in considerable research on fruit thinning and widespread commercial application of this practice. Heavy flowering intensity in some crop species results in economic disadvantages beyond the problems of excessive cropload and resultant small fruit size. Many species flower profusely and have initial fruit set that greatly exceeds tree capacity, resulting in abscission of numerous flowers and fruitlets. Abscised organs can represent a substantial amount of carbohydrates and nutrients, compromising availability of these materials at critical periods in flower and fruit development. The potential implications of this process are best exemplified in `Navel' orange [Citrus sinensis (L.) Osbeck], where an increase in flowering beyond intermediate intensity results in a reduction in both initial fruit set and final fruit yield at harvest. In several species, there is evidence that fruit size may be reduced by excessive flowering, even when cropload is quickly adjusted to an acceptable level. These data suggest that further research on the advantages of controlling flowering intensity is warranted.
and Browning, 1993 ). Although high rates of GA 3 have been investigated as a cropload management strategy for ‘Bing’ the season after application ( Lenahan et al., 2006 ; Proebsting and Mills, 1974 ), significantly lower return bloom severely
Whole fruit clusters were collected from three shoot types: terminal and lateral shoots without secondary growth, and shoots with secondary growth. Fruit per cluster was counted and nuts were individually weighed, shelled and graded. Return bloom of the same shoots was measured. Results indicated that cluster size of lateral bearing shoots was negatively related to next year's average kernel weight, nut weight, and kernel percentage. However, only kernel percentage was related to cluster size on terminal bearing shoots, and none of these parameters were related to cluster size on shoots with secondary growth. Cluster size and total kernel weight per shoot were positively related for the three shoot types. Return bloom of terminal shoots was negatively related to cluster size, but cluster size did not affect return bloom of the other shoot types.
The development of a complete and healthy early season canopy of spur leaves, and later addition of bourse leaves, is essential for fruit set, fruit growth and quality in apple. The present study was undertaken to evaluate the temporal role of spur leaves and bourse shoots on fruit set, growth and return bloom in three apple cultivars and fruit Ca Level at harvest in two cultivars.
Individual flowering spurs on mature wood of “Cox's Orange Pippin”, “Golden Delicious” and “Crispin” apple trees were modified by removing the spur leaves, the bourse shoot, or both, at full bloom and two, four and eight weeks afterwards. Leaf removal reduced fruit set, yield (as fruit number and not size), fruit calcium level at harvest, and return bloom. Defoliationhad its greatest effect on fruit calcium level when done early in the season and plots of this against treatment time suggested a curvilinear relationship. Return bloom was dependent on the presence of the bourse shoots on the spur but not on spur leaves. Return bloom of all three cultivars declined with the number of fruitlets per spur four weeks after full bloom.
BA, NAA, and carbaryl at 75, 6, and 600 mg·liter-1, respectively, were applied alone or in combination to `Starkrimson Delicious' in 1989 and `Redspur Delicious' apples (Malus domestica Borkh.) in 1990. BA was effective alone, but when combined with carbaryl it thinned excessively. Thinning failed when BA was combined with NAA because many seedless pygmy fruit were formed and they persisted until harvest. BA and carbaryl were more effective than NAA at increasing return bloom. Return bloom was more closely related to total seed count than to final set. BA improved flesh firmness at harvest and after cold storage. None of the treatments influenced the development of calcium-related storage disorders following air storage. Chemical names used: benzyladenine (BA); naphthaleneacetic acid (NAA).
Fruit of `Mohawk' in 1986 and 1988 and `Shoshoni' pecan [Carya illinoensis (Wangenh.) C. Koch] in 1986 were thinned during early August using a pecan shaker with modified shaker pads. Fruit removed ranged from 44% to 57% of the crop load. Fruit thinning increased nut size of `Mohawk' in both years, but did not affect nut size of `Shoshoni'. Kernel percentage of thinned `Mohawk' and `Shoshoni' trees increased, and kernel grade of `Mohawk' improved relative to unthinned trees. Return bloom of `Mohawk' was not affected either year by thinning, but return bloom on `Shoshoni' was increased by thinning. Mechanical fruit thinning appears to be a useful commercial tool until better thinning methods are available.
To investigate the effects of bud age on sprouting and flowering, bearing Clementine mandarin trees were hand-pruned at monthly intervals from late spring to fall. This pruning resulted in regrowth bearing axillary buds ranging in age from 9 to 5 months. After winter rest and during the return bloom, sprouting and flowering were assessed on axils on terminally positioned stems of these ages. The proportion of axillary buds sprouting and the number of spring shoots produced by each sprouting axillary site decreased with decreasing bud age. The proportion of axils sprouting one or more inflorescences, and the average number of flowers per stem also decreased with decreasing bud age. The number of axillary sites per stem, also significantly affected sprouting and flowering. Our results demonstrate the potential of hand-pruning to manipulate sprouting and return bloom depending on when in the summer or autumn the trees are pruned.
Postbloom applications of benzyladenine (BA) thinned young fruitlets of mature `Empire' apple trees (Malus domestica Borkh.) as well as or better than NAA or carbaryl (CB). BA increased fruit weight more effectively than either NAA or CB. Promalin (PR) was less effective than BA for both thinning and fruit-weight increase. In 1990, both BA and PR reduced fruit set up to 29 days after full bloom, but PR showed less thinning activity. BA and NAA produced independent and additive thinning responses when tank-mixed. Effects of all thinners on foliar mineral-nutrient concentrations were associated with changes in fruit load. BA increased return bloom as much or more than NAA or CB. PR did not affect return bloom. Chemical names used: N -(phenylmethyl)-1 H -purine-6-amine [benzyladenine (BA)]; BA plus gibberellins A, and A, [Promalin (PR)]; 1-naphthaleneacetic acid (NAA); 1-naphthalenyl methylcarbamate [carbaryl (CB)].
In 2001 and 2002, we imposed a wide range of croploads (0-15 fruits/cm2 of TCA) on 4- and 5-year-old Honeycrisp/M.9 trees by manual hand thinning soon after bloom to define appropriate croploads that give adequate repeat bloom and also the best fruit quality. At harvest each year we evaluated fruit ripening and quality. Samples were stored for 5 months in air at 38 °F and 33 °F and evaluated for fruit firmness and storage disorders. Cropload was negatively correlated with tree growth, return bloom, fruit size, fruit red color, fruit sugar content, fruit starch content, fruit firmness, fruit acidity, fruit bitter pit, fruit senescent breakdown, fruit rot and fruit superficial scald, but was positively correlated with leaf blotch symptoms, fruit internal ethylene concentration at harvest, and fruit soggy breakdown. There was a strong effect of cropload on fruit size up to a cropload 7, beyond which there was only a small additional effect. Although there was considerable variation in return bloom, a relatively low cropload was required to obtain adequate return bloom. Fruit red color was reduced only slightly up to a cropload of 8 beyond which it was reduced dramatically. The reduced fruit color and sugar content at high croploads could indicate a delay in maturity of but, fruits from high croploads were also softer, had less starch and greater internal ethylene. It that excessive croploads advance maturity. Overall, croploads greater than 10 resulted in no bloom the next year, and poor fruit size, color and flavor, but these fruits tended to have the least storage disorders. Moderate croploads (7-8) resulted in disappointing return bloom and mediocre fruit quality. For optimum quality and annual cropping, relatively low croploads of 4-5 were necessary.