Using Gibberellic Acid in California Citrus

Craig Kallsen, University of California Agriculture and Natural Resources (UCANR) citrus and pistachio farm advisor for Kern County, offered suggestions for the use of gibberellic acid (GA3) on citrus in the San Joaquin Valley. Highlights follows:

• Late September to mid-October was found to be the best time to apply GA3 to navels for reducing puff and crease and rind staining and for maintaining a more juvenile rind longer. Applying the GA3 two weeks before the fruit begins to change color from green to orange (called “color break”) remains a handy rule-of-thumb.
• Treating with an auxin (an isopropyl ester of 2,4-D is registered for this purpose) in November or early December is necessary if fruit is treated with GA3. The auxin prevents fruit from dropping too early.
• Uptake of GA3 by the peel is improved if the spray solution is acidic. A pH of about 4 to 5 is recommended. Several acidifying agents and products are available to accomplish this.
• Growers have obtained good results with GA3 applications using the labeled rates on a weight-of-product-per-acre basis using dilute or concentrated sprays. Good spray coverage of the fruit is essential, and better coverage is more likely with higher spray volumes.
• It’s common for a Kern County navel grower to report a significant drop of fruit and leaves as a result of a GA3 spray. Usually in these cases, GA3 was sprayed within a week or two of a narrow-range oil spray. Erring on the side of caution suggests avoiding spraying petroleum oils and GA3 within a few weeks of each other.
• GA3 works best on blocks of fruit that normally hold well on the tree. A good strategy is to harvest blocks that are prone to early rind breakdown first and to treat only blocks where the fruit naturally holds longer with GA3.
• Sometimes fruit does not grow as quickly as a grower would like, and a block that was scheduled for an early or mid-season harvest may be rescheduled for a late-season harvest. GA3 applications can still delay harvest if treated later than October. Do not apply GA3 to fruit that is in the process of changing color because a permanently two-tone fruit may result. If the fruit is in the process of changing color, wait until the fruit has turned completely orange and then apply GA3.
• Late-maturing navels are not as likely to require the addition of gibberellic acid and 2,4-D to produce high-quality fruit late in the season.

See Kallsen’s full article on gibberellic acid use here.

Source: UCANR

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