Agriculture: Citrus Pest Management Guidelines

Increasing Fruit Size with 2,4-Dichlorophenoxyacetic Acid (2,4-D)

Note: Fruit-sizing sprays require excellent coverage.

Precautions When Using 2,4-D

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

  • Avoid 2,4-D spray drift to susceptible plants, which include cotton, grapes, roses, beans, peas, alfalfa, lettuce, ornamentals, and all broadleaf species.
  • Applying 2,4-D shortly before or during a flush of growth may damage vegetative and reproductive growth. This may result in lower fruit production, especially if the spring flush is affected.

Be sure to review the effect of this treatment on mature fruit remaining on the tree in the section REDUCING FRUIT DROP WITH 2,4-DICHLOROPHENOXYACETIC ACID (2,4 D).

  Variety Amount per acre REI‡ Application timing
    (g a.e.= grams acid equivalent) (hours) (based on fruit size)
Always read the label of the product being used.
 
A. NAVEL ORANGES and VALENCIAS* 23 g a.e. in water spray 12 3/16–1/4 inch (5–6 mm)
. . . or . . .
30 g a.e. in water spray 1/4–1/2 inch (6–13 mm)
. . . or . . .
38 g a.e. in water spray 1/2–5/8 inch (13–16 mm)
. . . or . . .
45 g a.e. in water spray 5/8–3/4 inch (16–19 mm)
COMMENTS: May cause an increased roughness of the rind. For Valencia oranges, also controls mature fruit drop and may slightly delay granulation in the new crop. For navel oranges, may decrease fruit splitting.
 
B. GRAPEFRUIT* 23 g a.e. in water spray 12 1/4–3/8 inch (6–9 mm)
. . . or . . .
30 g a.e. in water spray 3/8–5/8 inch (9–16 mm)
. . . or . . .
38 g a.e. in water spray 5/8–3/4 inch (16–19 mm)
. . . or . . .
45 g a.e. in water spray 3/4–1 inch (19–25 mm)
COMMENTS: Also controls mature fruit drop.
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.
* Note:

(1) Do not apply to trees less than 6 years old.

(2) Do not apply within 7 days of harvest (PHI=7 days).

(3) 2,4-D 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.

(4) Use an isopropyl ester formulation of 2,4-D containing 3.34 or 3.36 lb of acid equivalent per gallon. These formulations provide about 1,520 g acid equivalent/gal, 402 g acid equivalent/liter, 0.402 g acid equivalent/ml, or 12 g acid equivalent/fl oz. An example for 30 g acid equivalent/acre: (30g)/(0.402 g/ml) = 75 ml. Thus, 30 g would be contained in 75 ml or 2.5 fl oz of formulation. Apply this to one acre in volumes up to 500 gal. A minimum of 500 gal per acre is recommended for mature trees, which results in a 16 ppm 2,4-D solution.

Text Updated: 01/19
Treatment Table Updated: 01/19