Agriculture: Citrus Pest Management Guidelines

Increasing Fruit Set with Gibberellic Acids (GA3)

Precautions When Using GA3

Observe all precautions below and comments given with each plant growth regulator use:

  • GA3 is slowly hydrolyzed by water and rapidly converted into an inactive isomer in highly alkaline solutions. Protect liquid and powder formulations from moisture and do not add GA3 to highly alkaline spray mixtures.
  • Although GA3 seems to be stable in solutions up to pH 11 for short periods of time (2 hours), its activity is diminished rapidly at the high pH values found in Bordeaux and whitewash mixtures. Keep the pH of your GA3 solutions below pH 8, or lower according to manufacturer's label.
  • Some observational evidence suggests that foliar petroleum oil sprays applied within two weeks of GA3 may result in significant leaf drop.

Be sure to review the effect of this treatment on fruit remaining on the tree in the section DELAYING FRUIT SENESCENCE WITH GIBBERELIC ACID (GA3).

Variety Amount per acre
REI‡ Application timing
    (g a.i. = grams active ingredient) (hours)  
Always read the label of the product being used.
Note: Certain formulations emit high amounts of volatile organic compounds (VOCs); use low-VOC formulations of gibberellins. Regulations affect the use of high-VOC gibberellic acid on citrus for the San Joaquin Valley from May 1 to October 31, 2020. Growers, PCAs and interested parties can learn when high-VOC prohibitions are in effect through the VOC e-mail list. Join at www.cdpr.ca.gov and click on "Join E-lists". Review the Department of Pesticide Regulation's updated fact sheet (PDF).
 
A. CLEMENTINE MANDARIN 1–8 g a.i. in water spray 4 Make 1 to 2 applications between 50% petal fall and 3 weeks after petal fall
COMMENTS: Use a dilute spray with sufficient spray volume for adequate coverage of tree canopy. Do not apply mixtures of materials that produce a pH higher than 8.0 (see precautions above). Generally, more fruit will set with two applications, higher rates, earlier applications, and climate conditions that favor fruit set. Differences in type of Clementine mandarin have been observed to interact with these factors and affect the degree of fruit set achieved. Reduction in final fruit size can occur on occasion as a result of excessive fruit set. GA3 seems to be compatible with urea, potassium foliar sprays, zinc and manganese micronutrient sprays, and neutral copper sprays, but the timing of its applications may not coincide with the best time for nutrient sprays.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
Text Updated: 01/19
Treatment Table Updated: 01/19