In three trials, 2004 crop loads were adjusted at the balloon stage of blossom development on heavily cropped whole apple trees by clipping all flower pedicels within a cluster while leaving the spur intact. Trees were adjusted to 0% crop (all flowers removed), 50% crop (half of all clusters removed), or left as 100% crop (no flowers removed). On `Cameo'/Bud.9, 400 ppm GA4+7 were applied to trees of each crop level at petal fall, 10 mm, 20 mm, or left unsprayed. At each crop load, GA4+7 marginally diminished the 2005 return bloom regardless of application timing, but the 2004 crop level was far more influential in 2005 flowering. In a second `Cameo'/Bud.9 trial, 0, 300, 600, or 900 ppm ethephon were applied to whole trees of each crop level at 45 DAFB. Ethephon generally demonstrated a rate response in improving the 2005 return bloom, but the 2005 flowering was more dramatically influenced by 2004 crop levels. On `Honeycrisp'/M.9, 300 ppm GA4+7 were applied to whole trees of each crop level at 10 mm. GA4+7 diminished 2005 return bloom at the 50% crop load, but spray effects were not as clear at the extreme 2004 crop levels. These results suggest that commercial floral inhibitors and promoters have difficulty overcoming endogenous effects of heavy or light bloom and crop in severely alternating apple trees. In a fourth trial, lightly cropped organic `Fuji'/MM.106 trees were sprayed with 0, 150, 300, or 450 ppm GA4 at petal fall, 10 mm, or 20 mm timings in 2004. The 2005 return bloom was inversely correlated with spray rates, with 10 mm showing more floral inhibition than other timings. Overall, `Cameo' was less sensitive to GA and ethephon than `Honeycrisp' or `Fuji'.
Tory Schmidt, Don Elfving and Jim McFerson
Don C. Elfving and Dwayne B. Visser
Improving lateral branch development in young sweet cherry trees without reliance on pruning is a desirable component of tree training programs, especially for high-density systems. Applications of two proprietary formulations of 6-benzyladenine and gibberellins A4 and A7 (Promalin, Valent Biosciences, Walnut Creek, Calif.; and Perlan, Fine Americas, Walnut Creek, Calif.) to individual buds or intact bark of unpruned sweet cherry central leader shoots at green-tip had little effect on lateral shoot growth from buds or on distribution of new shoot growth along the treated leader shoots. Scoring, nicking, or notching cuts alone also had inconsistent effects on shoot development and distribution. In some trials, bud removal (or disbudding, removing every fourth bud on 1-year-old shoots) produced limited improvement of lateral shoot development and vertical distribution. Combining nicking, notching, scoring, or bark scraping with the application of cytokinin–gibberellic acid solution to the cut area greatly improved both number of shoots developed and the numbers originating from the lower portions of treated leader shoots. Removing the physical barrier to bioregulator product contact with active tissues was a primary factor in improving treatment efficacy.
Don C. Elfving and Dwayne B. Visser
The height above the bud union at which induced feathers develop on fruit trees in the nursery is an important determinant of tree quality for an intended market. The bioregulators cyclanilide (CYC; Bayer Environmental Science, Research Triangle Park, NC) and a proprietary formulation of 6-benzyladenine and gibberellins A4 and A7 (Promalin [PR]; Valent BioSciences, Walnut Creek, CA) affected the final height above the union of the lowest induced sylleptic shoot (feather) differently in apple and sweet cherry trees in the nursery. In apple, both products resulted in the lowest induced feather developing at approximately 4 to 20 cm below the height of the central leader shoot tip at the time of bioregulator application. In sweet cherry, the lowest induced feather typically originated starting approximately 2 to 20 cm above the central leader shoot tip height at the time of bioregulator application. Nursery tree height can serve as a suitable criterion for timing bioregulator applications to obtain feathers starting within a specific range of height above the bud union as long as species-specific feathering response characteristics are taken into account. Chemical names used: 1-(2,4-dichlorophenylaminocarbonyl)-cyclopropane carboxylic acid (Cyclanilide), N-(phenylmethyl)-1H-purine-6-amine + gibberellins A4A7 (Promalin), polyoxyethylenepolypropoxypropanol, dihydroxypropane, 2-butoxyethanol (Regulaid).
Don C. Elfving and Dwayne B. Visser
A new bioregulator, cyclanilide (CYC, Bayer Environmental Science, Research Triangle Park, NC 27709), was compared with a proprietary formulation of 6-benzyladenine and gibberellins A4 and A7 [Promalin (PR), Valent BioSciences, Walnut Creek, Calif.] for branching effects on sweet cherry trees. CYC stimulated the formation of lateral shoots on current-season's shoot growth under both orchard and nursery conditions. In the nursery CYC was as effective or better for feathering compared to PR in all cherry cultivars tested. There were no synergistic effects of CYC/PR tank mixes on feather development. Crotch angles of induced feathers were not different from the angles of feathers that formed spontaneously. The growth of CYC-induced feathers was sufficient to produce acceptable quality feathered trees. Trunk caliper of nursery trees was either not affected or reduced to a very minimal degree. CYC is effective for lateral branch induction in sweet cherry, especially in the nursery. Chemical names used: 1-(2,4-dichlorophenylaminocarbonyl)-cyclopropane carboxylic acid (cyclanilide); N-(phenylmethyl)-1H-purine-6-amine + gibberellins A4 and A7 (Promalin); polyoxyethylenepolypropoxypropanol, dihydroxypropane, 2-butoxyethanol (Regulaid).
Don C. Elfving and Dwayne B. Visser
A new bioregulator, cyclanilide (CYC, Bayer Environmental Science, Montvale, N.J.), was tested for growth-related effects on apple trees over three years. Although treatment with CYC produced small reductions in shoot length, its principal effect was to stimulate the formation of lateral shoots on current-season's shoot growth and from spurs on older wood. CYC treatment of `Scarletspur Delicious' apple trees in the nursery more than doubled the formation of well-developed feathers with wide crotch angles (≈60°) and with no effect on final tree height. CYC appeared to flatten the apples and reduce fruit size in one trial. CYC appears promising for lateral branch induction in apple, especially in the nursery. Chemical names used: 1-(2,4-dichlorophenylaminocarbonyl)-cyclopropane carboxylic acid (Cyclanilide); calcium 3-oxido-4-propionyl-5-oxo-4-propionylcyclohex-3-enecarboxylate (prohexadione-Ca, Apogee); N-(phenylmethyl)-1H-purine-6-amine + gibberellins A4A7 (Promalin); polyoxyethylenepolypropoxypropanol, dihydroxypropane, 2-butoxyethanol (Regulaid).
David Sugar, Don C. Elfving and Eugene A. Mielke
The effects of prohexadione-calcium (P-Ca) on fruit size and return bloom in three pear cultivars were evaluated in Medford and Hood River, Ore., and in Cashmere, Wash. A variety of treatment dosages and timings was applied to 4- and 5-year-old trees in 2 years of study. Fruit weight of `Bosc' and `Red Anjou' pears was not affected by P-Ca treatments at any location in either year. However, decreased weight of `Bartlett' pear fruit was associated with all P-Ca treatments in 1999 in Medford except for 83 ppm applied at 2.5 to 6.0 cm shoot growth (first treatment) plus 2, 4, 6, and 8 weeks after first treatment (WAFT) and 125 ppm applied at 2.5 to 6.0 cm growth plus 4 WAFT. `Bartlett' fruit weight was reduced in Medford in 2000 by all treatments except 125 ppm applied at 2.5 to 6.0 cm growth plus 4, 8, and 12 WAFT. In Cashmere in 2000, mean weight of `Bartlett' and `d'Anjou' fruit was reduced by treatments with 83 or 125 ppm applied at 2.5 to 6.0 cm growth plus 2, 4, and 6 WAFT and of `Bosc' pear by all treatments that included more than a single application of P-Ca. Crop load was not significantly different among treatments at any location. Return bloom in the year following P-Ca treatment was reduced in `Bosc' pears by some to most treatments at all locations in both years. In contrast, return bloom was reduced in `Bartlett' and `Anjou' pears only in Hood River in 1999.
Adam Dale, Don C. Elfving and Craig K. Chandler
In greenhouse and field studies, benzyladenine (BA) and gibberellic acid (GA3) applied together as a foliar spray increased runner production in dayneutral strawberries (Fragaria ×ananassa Duch.) but not when applied separately. Runner production increased linearly with increased BA concentration to 1800 mg·L–1. At high dosages, GA3-treated plants produced elongated internodes that, in the field, led to fewer daughter plants. In Florida, daughter plants derived from plants sprayed with the growth regulators increased yield by up to 10% in fruiting experiments. To induce runnering in the field and greenhouse, a treatment with BA at 1200 mg·L–1 and GA3 at 300 mg·L–1 is recommended. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine (benzyladenine); gibberellic acid A3; gibberellic acids A4 and A7.
Don C. Elfving, Gregory A. Lang and Dwayne B. Visser
Prohexadione-Ca (P-Ca) and ethephon (ETH) were evaluated as potential inhibitors of growth and promoters of early flowering for high density orchard management of sweet cherry (Prunus avium L.) trees on vigorous rootstocks. Single applications (P-Ca at 125 to 250 mg·L-1 active ingredient (a.i.) or ETH at 175 to 200 mg·L-1 a.i.) to young, nonfruiting sweet cherry trees produced short-term, generally transient reductions in terminal shoot elongation, and did not stimulate flower bud formation. Tank-mix applications (P-Ca + ETH) usually produced a stronger, possibly synergistic, reduction in shoot growth rate. Single tank-mix applications either increased subsequent flower bud density on previous season shoots or had no effect; when a second application was made three weeks later to the same trees, subsequent flower bud density on previous season shoots and spurs on older wood increased ≈3-fold over untreated trees. Yield efficiency (g·cm2 trunk cross-sectional area) also increased nearly 3-fold. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon); calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene carboxylate (prohexadione-Ca); polyoxyethylene polypropoxypropanol, dihydroxypropane, 2-butoxyethanol (Regulaid); aliphatic polycarboxylate, calcium (Tri-Fol).
Larry E. Schrader, Jianguang Zhang, Jianshe Sun, Jizhong Xu, Don C. Elfving and Cindy Kahn
Postharvest changes in flesh firmness, soluble solids concentration (SSC), and titratable acidity (TA) associated with increasing severity of sunburn browning of apples (Malus ×domestica Borkh.) were investigated over time in regular atmosphere cold storage. In 2005, ‘Gala’ apples were harvested at maturity and sorted into five classes ranging from no sunburn (Sb-0) to severe sunburn browning (Sb-4). Flesh firmness, SSC, and TA were measured on flesh tissue beneath the sunburned area of the apples at harvest and at monthly intervals for 6 months. In 2006, a similar protocol was used for ‘Gala’, ‘Golden Delicious’, ‘Jonagold’, ‘Granny Smith’, and ‘Fuji’ apples, except that these fruit quality traits were determined at harvest and after 3 and 6 months in regular atmosphere cold storage. Flesh firmness and SSC increased, but TA decreased both years in all cultivars as sunburn severity increased from Sb-1 to Sb-4. The patterns of higher firmness with more severe sunburn browning persisted during cold storage even though firmness in all classes of fruit decreased gradually with time in cold storage. The patterns of lower TA as severity of sunburn increased also persisted during cold storage, but TA declined more markedly in apples with more severe sunburn. The ratio of SSC to TA (SAR) increased as the severity of sunburn increased in all five cultivars. The SAR also increased dramatically from harvest to 3 and 6 months after harvest with ratios exceeding 200 in Sb-4 of some cultivars after 6 months storage. This occurred because TA declined very markedly as time in cold storage increased. Relative water concentration of tissue in sunburned areas of apples declined as the severity of sunburn increased, and helps to account for the higher SSC and firmness observed in sunburned apples.
Torrance R. Schmidt, Don C. Elfving, James R. McFerson and Matthew D. Whiting
Gibberellins inhibit flowering in apple (Malus domestica) and show promise as tools to promote annual bearing. The authors validated the efficacy of gibberellic acid (GA) to reduce return bloom dramatically in two biennial cultivars. ‘Honeycrisp’ fruit treated in 2004 with GA4+7 at 0, 200, 400, or 600 mg·L−1 demonstrated advanced maturity in terms of starch levels, flesh firmness, and titratable acidity, whereas ‘Cameo’ fruit showed variable treatment effects. In 2005, 0, 300, 600, 900, or 1200 mg·L−1 GA4+7 was applied to ‘Cameo’, and fruit maturity was once again unaffected. Two commercial GA products (GA4, GA4+7) were applied in 2005 to ‘Honeycrisp’ at 400 mg·L−1. Both formulations caused fruit to have less flesh firmness and acidity, and increased levels of starch conversion compared with the untreated control at harvest and after 140 d of common storage. All GA treatments in all four trials profoundly diminished flowering in the season after treatment. Results demonstrate differences in sensitivity to GA between the two cultivars.