UC IPM: Information about Increasing Fruit Size with 2,4-D in Citrus

UC Pest Management Guidelines

Citrus

Increasing Fruit Size with 2,4-D

(Reviewed 9/08, updated 3/10)

In this Guideline:

Variety

Amount to Use (g a.e./a = grams acid equivalent/acre)

Time

CAUTION: Avoid 2,4-D spray drift to susceptible plants, which include cotton, grapes, roses, beans, peas, alfalfa, lettuce, ornamentals, and all broadleaf species. 2,4-D has a 12 hour restricted entry interval.

VALENCIA and NAVEL ORANGES*

23 g a.e./a in water spray

3/16–1/4 inch (5–6 mm)

. . . or . . .

30 g a.e./a in water spray

1/4–1/2 inch (6–13 mm)

. . . or . . .

38 g a.e./a in water spray

1/2–5/8 inch (13–16 mm)

. . . or . . .

45 g a.e./a in water spray

5/8–3/4 inch (16–19 mm)

COMMENTS: Fruit-sizing sprays require excellent coverage. May cause an increased roughness of the rind. For Valencia oranges, also controls mature fruit drop and may slightly delay granulation in new crop. For navel oranges, may decrease fruit splitting.

GRAPEFRUIT*

23 g a.e./a in water spray

1/4–3/8 inch (6–9 mm)

. . . or . . .

30 g a.e./a in water spray

3/8–5/8 inch (9–16 mm)

. . . or . . .

38 g a.e./a in water spray

5/8–3/4 inch (16–19 mm)

. . . or . . .

45 g a.e./a in water spray

3/4–1 inch (19–25 mm)

COMMENTS: Fruit-sizing sprays require excellent coverage. Also controls mature fruit drop.

MANDARIN and

MANDARIN HYBRIDS*

40 g a.e./a in water spray

21–35 days after 75% petal fall

COMMENTS: Specific use is covered by EPA SLN No. CA-040027. Fruit-sizing sprays require excellent coverage, minimum of 500 gallons per acre. Valid until withdrawn, suspended, or canceled by the United States Environmental Protection Agency (US EPA), the manufacturer, the 24(c) registrant, or the California Department of Pesticide Registration. CAUTION: Application of 2,4-D can cause fruit dryness in mandarin and mandarin hybrids, causing them to be less juicy; e.g., 'Nules' Clementine or in orchards prone to granulation.

Note: (1) Do not apply to trees less than 6 years old. (2) Do not apply within 7 days of harvest. (3) Do not enter or allow worker entry into treated area during the restricted entry interval (REI) of 12 hours. (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 152 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 1 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).

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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How to Manage Pests

UC Pest Management Guidelines

Citrus

Increasing Fruit Size with 2,4-D

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