Attempts to control alternate cropping of Valencia orange by inhibiting flower formation with gibberellic acid

1978 ◽  
Vol 18 (91) ◽  
pp. 309 ◽  
Author(s):  
PT Gallasch
Keyword(s):  
Gibberellic Acid ◽  
No Reduction ◽  
South Australia ◽  
Flower Formation ◽  
Mature Fruit ◽  
Mature Trees ◽  
Valencia Orange ◽  
Orange Trees

Gibberellic acid (GA) was sprayed on whole Valencia orange trees in 1971 at Loxton in South Australia with the aim of reducing the size of the heavy crop and the alternate cropping cycle. Sprays were applied in June or July at 25 p.p.m. but there was no reduction in mature fruit weights in 1972. In 1973, sprays of GA at 25 p.p.m, were applied twice, about two weeks apart, commencing on either May 7 or 22. In the following November treated trees had 75 per cent fewer fruitlets, but by the time fruit were mature, trees had fully compensated for this early reduction in fruit numbers by increased set and reduced December drop. Again the weight of mature fruit was not reduced at the timings and concentrations used and hence GA cannot be recommended for the control of alternate cropping.

Effect of time of harvest on alternate cropping yields and fruit quality of Valencia orange trees

1978 ◽  
Vol 18 (92) ◽  
pp. 461 ◽  
Author(s):  
PT Gallasch
Keyword(s):  
Fruit Quality ◽  
South Australia ◽  
Mature Fruit ◽  
Late Season ◽  
Valencia Orange ◽  
The Common ◽  
Orange Trees ◽  
Early Harvest ◽  
Time Of Harvest

At Loxton, South Australia, early harvest of heavy, and late harvest of light, Valencia orange crops was compared with the common practice: early harvest of light and late harvest of heavy crops. These treatments were compared with two years of early, mid- or late season harvests. Early harvest of heavy and late harvest of light crops changed the 3.1:1.0 alternate cropping cycle to 1.1:10 and increased the light crop by 101 per cent compared with the common district practice which gave a 3.2 : 10 cycle. Consistent early and mid-season harvests reduced the alternate cropping ratio to 1.3 : 1.0 and 1.4 : 1.0 respectively, produced 14 per cent more fruit than the common district practice and avoided harvesting the light crop late, when fruit quality is poor. Mature fruit weights from trees consistently harvested late were 27 per cent lower than those trees harvested mid-season.

Control of alternate cropping of Valencia orange with ethephon and napthalene acetic acid

1978 ◽  
Vol 18 (90) ◽  
pp. 152 ◽  
Author(s):  
PT Gallasch
Keyword(s):  
Acetic Acid ◽  
South Australia ◽  
Fruit Weight ◽  
Mature Fruit ◽  
Crop Load ◽  
The Third ◽  
Load Following ◽  
Valencia Orange ◽  
Leaf Drop ◽  
Orange Trees

Three experiments were done in the Riverland district of South Australia with the aim of controlling alternate cropping of mature Valencia orange trees by chemical thinning. In experiment 1, 300 p.p.m. ethephon was applied in either October, November or December. In experiment 2, sprays of either 200, 250, 300 or 350 p.p.m. ethephon were applied in late November. In experiment 3, sprays of either ethephon, NAA or a mixture of both were applied in early December. Sprays of ethephon in December were more effective than in October, and resulted in a 40 per cent reduction of mature fruit weight in a heavy crop year. All concentrations of ethephon of 250 p.p.m, or more reduced the heavy crop load, and in the following year increased light crops. A 15 per cent reduction in crop load following sprays of 250 p.p.m, gave even cropping trees. Treated trees produced, over two years, 10 per cent more fruit weight than control trees. Fruit from treated trees were larger in the heavy crop year and smaller the following year. In the third experiment, 300 p.p.m. ethephon reduced the mature crop by 31 per cent and 500 p.p.m. NAA reduced it by 18 per cent. A mixture of the two chemicals effected a 51 per cent reduction in crop load, but the NAA did not significantly reduce leaf drop. NAA at 500 p.p.m. resulted in the most even cropping trees.

scholarly journals Late-season `Valencia' Orange Mechanical Harvesting with an Abscission Agent and Low-frequency Harvesting

HortScience ◽  
2006 ◽  
Vol 41 (3) ◽  
pp. 660-663 ◽  
Author(s):  
Jacqueline K. Burns ◽  
Fritz M. Roka ◽  
Kuo-Tan Li ◽  
Luis Pozo ◽  
Richard S. Buker
Keyword(s):  
Citrus Sinensis ◽  
Low Frequency ◽  
Mature Fruit ◽  
Fruit Removal ◽  
Immature Fruit ◽  
Late Season ◽  
Valencia Orange ◽  
Significant Difference ◽  
Orange Trees

An abscission agent (5-chloro-3-methyl-4-nitro-1H-pyrazole [CMNP]) at 300 mg·L–1 in a volume of 2810 L·ha–1 was applied to Valencia orange trees [Citrus sinensis (L.) Osb.] on 22 May 2004. At this time, immature and mature fruit were present on the tree simultaneously. Three days after application, fruit were mechanically harvested using a trunk-shake-and-catch system. The power to the shaker head was operated at full- or half-throttle (FT or HT, respectively), and the duration of trunk shaking was 2 seconds at FT or 4 seconds at FT and HT. Mature fruit removal percentage and number of immature fruit removed, and fruitlet weight and diameter were determined. Mature fruit removal percentage with 2 seconds at FT or 4 seconds at FT harvesting ±CMNP, or 4 seconds at HT + CMNP was not significantly different and ranged between 89% to 97%. Harvesting at 4 seconds HT without CMNP removed significantly less mature fruit than any treatment. CMNP did not affect immature fruit removal by the trunk shaker. Harvesting at 4 seconds at HT removed significantly less immature fruit than 2 seconds at FT or 4 seconds at FT. No significant difference in fruitlet weight or diameter was measured between any trunk shaker harvest operation and CMNP treatment. Trunk shaking frequency was estimated to be 4.8 and 8.0 Hz at HT and FT, respectively. Yield in 2005 was determined on the same trees used for harvest treatments in 2004. CMNP did not impact yield. No significant difference in yield was seen between the hand-picked control and 4 seconds at HT, whereas yield in the remaining treatments was lower. The results demonstrate that CMNP application combined with low frequency trunk shaker harvesting can achieve high percentage of mature fruit removal with no significant impact on return yield of the following crop.

Regulating Valencia orange crops with CEPA (2-chloroethyl phosphonic acid) - preliminary studies

1974 ◽  
Vol 14 (71) ◽  
pp. 835 ◽  
Author(s):  
T GallaschP
Keyword(s):  
Phosphonic Acid ◽  
South Australia ◽  
Fruit Yield ◽  
Leaf Fall ◽  
Mature Fruit ◽  
Phytotoxic Effects ◽  
Valencia Orange

The effects of chemicals on fruitlet thinning of Valencia oranges were studied in two experiments at Loxton, South Australia. In the first experiment 50 p.p.m. 245T, 2000 p.p.m. N.A.A. and 250 or 1000 p.p.m. CEPA all caused significant thinning but 245T had phytotoxic effects. In the second experiment with several concentrations of CEPA, both 524 and 1048 p.p.m. caused significant leaf and fruitlet drop, whereas 262 p.p.m. caused a significant reduction of 55 per cent in mature fruit yield without any significant leaf fall.

scholarly journals Effects of Exogenous Gibberellic Acid in Huanglongbing-affected Sweet Orange Trees under Florida Conditions – I. Flower Bud Emergence and Flower Formation

HortScience ◽  
2021 ◽  
pp. 1-11
Author(s):  
Lisa Tang ◽  
Garima Singh ◽  
Megan Dewdney ◽  
Tripti Vashisth
Keyword(s):  
Gibberellic Acid ◽  
Sweet Orange ◽  
Fruit Production ◽  
Colletotrichum Acutatum ◽  
Flower Formation ◽  
Flower Bud ◽  
Climate Conditions ◽  
Bloom Period ◽  
Flower Bud Formation ◽  
Orange Trees

Under Florida conditions, sweet orange (Citrus sinensis) affected by Huanglongbing {HLB [Candidatus Liberibacter asiaticus (CLas)]} frequently exhibits irregular flowering patterns, including off-season flowering and prolonged bloom period. Such patterns can increase the opportunity for temporal and spatial proliferation of pathogens that infect flower petals, including the fungal causal agent for postbloom fruit drop (PFD) Colletotrichum acutatum J.H. Simmonds. For the development of strategies to manipulate flowering, the effects of floral inhibitor gibberellic acid (GA3) sprayed monthly at full- and half-strength rates (49 and 25 g·ha−1, or 33 and 17 mg·L−1, respectively) with different regimens, starting from September and ending in November, December, or January, on the pattern of spring bloom were evaluated in field-grown HLB-affected ‘Valencia’ sweet orange at two locations in subsequent February through April for two separate years in this study. To further examine whether GA3 effects on flowering patterns vary in different cultivars, early-maturing ‘Navel’ sweet orange trees receiving no GA3 or full-strength GA3 monthly in September through January were included. Overall, for ‘Valencia’ sweet orange, monthly applications of GA3 at 49 g·ha−1 from September to December not only minimized the incidence of scattered emergence of flower buds and open flowers before the major bloom but also shortened the duration of flowering, compared with the untreated control trees. In addition, exogenous GA3 led to decreased leaf flowering locus t (FT) expression starting in December, as well as reduced expression of its downstream flower genes in buds during later months. When applied monthly from September through January at 49 g·ha−1, similar influences of exogenous GA3 on repressing flower bud formation and compressing bloom period were observed in ‘Navel’ sweet orange. These results suggest that by effectively manipulating flowering in HLB-affected sweet orange trees under the Florida climate conditions, exogenous GA3 may be used to reduce early sporadic flowering and thereby shorten the window of C. acutatum infection that causes loss in fruit production.

The use of gibberellic acid to control alternate cropping of Late Valencia sweet orange

1977 ◽  
Vol 28 (6) ◽  
pp. 1041 ◽  
Author(s):  
GI Moss ◽  
KB Bevington
Keyword(s):  
Gibberellic Acid ◽  
Sweet Orange ◽  
Poncirus Trifoliata ◽  
Minimum Concentration ◽  
Rough Lemon ◽  
Small Fruit ◽  
Valencia Orange ◽  
Orange Trees ◽  
Long Term Adverse Effects

The effect of spraying commercial gibberellic acid (GA) on alternate cropping and yield of Late Valencia orange trees was studied in detail at three sites over three seasons. Two applications of GA were applied at a minimum concentration of 25 ppm (in two experiments 0.75% emulsifiable oil was used as an adjuvant) 3 weeks apart during April and May for Dareton (on the River Murray) or June and early July for Yanco (Murrumbidgee Irrigation Areas) prior to the heavy-crop blossom. These sprays partly inhibited flowering and the subsequent heavy crop was reduced by up to 22% (by fruit number). In the next season there were more flowers and the light crop was increased by up to 57% at Dareton and 228% at Yanco. Some treatments practically eliminated alternate cropping while all reduced considerably the heavyllight crop ratio. Mean weight yields over 2 years were increased by up to 17% at Yanco and 16% at Dareton with mean increases for all successful GA treatments of 12.6% and 7.2% respectively. This represented an increase of 34 and 24 kg fruitltree. No long-term adverse effects on yield were found.Apart from re-greening of the fruit present at the time of spraying, fruit quality was not affected. There were fewer non-saleable small fruit at Yanco in the heavy crop as a result of the GA treatments, and a better range of fruit sizes in both the heavy and light crops. Trees on Rough Lemon rootstock responded well to GA treatments, especially in terms of increased yield in the light crop. Poncirus trifoliata rootstock was less responsive than Sweet Orange. This method might be used for the commercial control of alternate cropping of Late Valencia orange trees.

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