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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Citrus

Delaying Fruit Senescence with Gibberellic Acid (GA3)

(Reviewed 9/08, updated 9/08)

In this Guideline:
Variety Amount to Use (g a.e./a = grams acid equivalent/acre) Time
A. NAVEL ORANGES* 10–40 g a.i./a in water spray see comments below
  COMMENTS: Restricted entry interval (REI): 12 hours. Used to reduce rind staining, water spot, and sticky rind (delayed aging and softening of rind). Apply in Sept.–Nov. to groves that will be harvested later than Feb. 15 (San Joaquin Valley) or later than Mar. 1 (southern California). Preferred application time is 2 weeks before color break. If delayed coloring cannot be tolerated, apply after marketable color has developed. In both cases, there will be delayed rind aging but when it is applied after color has developed, considerable aging will have already occurred, resulting in less potential delay in aging. The effect of the later spray may be inadequate to provide the desired protection. Do not apply in mixtures containing lime or other caustic materials that produce a pH higher than 8.0 (see caution on E.2). Make application at least 3 days before or 3 days after whitewash (hydrated lime) and avoid January applications as they may decrease subsequent production. Treatment with GA3 probably lowers intensity of puffy rind and fruit appears to be less susceptible to postharvest decay and mechanical injury. GA3 may result in a minor amount of leaf and fruit drop. Occasionally, leaf drop and fruit drop is excessive. When this happens, twig dieback can occur. Including 2,4-D in the GA3 spray may reduce these negative effects. There is little need for delaying fruit senescence on young trees. This plus the possibility of excessive leaf drop argue against the application of GA3 to young trees.
 
B. VALENCIA ORANGES* 40–80 g a.i./a Aug.–Sept.
  COMMENTS: Restricted entry interval (REI): 12 hours. Used to reduce rind creasing and delay aging and softening of rind. Apply at an early stage of fruit development. Application at a later stage may lead to more regreening than is acceptable. Some regreening or slower color development should be expected in the target crop and some increased regreening of mature fruit, if present, may occur. To improve coverage, high spray volumes (500 gallons) are encouraged.
 
C. TANGERINE (MANDARIN) HYBRIDS* 20–40 g a.i./a see comments below
  COMMENTS: Restricted entry interval (REI): 12 hours. Used to delay rind aging and softening and to reduce puffiness of rind. Apply about 2 weeks before color break, but only to groves where early harvest will not occur as this treatment delays coloring; satisfactory color should not be expected until late January. Later GA3 applications may produce undesirable results: applications made during coloring may result in unacceptable variations in rind color and applications made after coloring may cause preharvest rind staining to occur. Do not apply in whitewash or other caustic materials that produce a high pH (see caution on E.2).
 
D. LEMONS* 10–20 g a.i./a Oct.–Dec.
  (nondesert areas)
  COMMENTS: Restricted entry interval (REI): 12 hours. Used to delay fruit maturity. Apply when target crop is 1/2 to 3/4 full size and still green. Reduces the number of small tree-ripe fruit and delays flowering, which shifts second year crop toward summer.
 
E. LIMES* 20 g a.i./a Sept.–Oct.
  (nondesert areas)
  COMMENTS: Restricted entry interval (REI): 12 hours. Used to delay rind coloration. Apply when target crop is 1/2 to 3/4 full size and still green. Use amount given for large mature trees and less for smaller trees.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Plant Growth Regulators
C. J. Lovatt, Botany and Plant Sciences, UC Riverside
Acknowledgment for contributions to Plant Growth Regulators:
C. W. Coggins, Jr., Botany and Plant Sciences, UC Riverside

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