How to Manage Pests

UC Pest Management Guidelines

Citrus

Preharvest Fruit Drop Control with 2,4-D

(Reviewed 9/08, updated 3/10)

In this Guideline:


Variety Amount to use (g a.e. = grams acid equivalent) Time

  Calculate impact of pesticide on air quality
 
Not all registered pesticides are listed. Always read label of product being used.
 
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.
 
A. NAVEL ORANGES* 30 g a.e./acre in water spray Sept.–Nov.
    . . . or . . .  
    15 g a.e./acre in water spray Dec.–Jan.
    . . . or . . .  
    45 g a.e./acre in hydrated lime spray Sept.–Nov.
  COMMENTS: The 45 g/acre treatment applied in hydrated lime (whitewash) is inferior to 30 g/acre applied in water. This is important during long harvest seasons. The preferred Oct.–Nov. treatment is a 30 g/acre water spray applied 3 days before or 3 days after whitewash. October through December sprays are commonly used and are generally effective. However, September, in particular, and October, as well, may be too early to provide good control when conditions favor fruit drop (warm winter, protracted harvest, etc.). On the other hand, January sprays may be somewhat risky, especially when environmental factors favor an earlier-than-usual spring flush of growth. More than one application of 2,4-D may be appropriate. For example, consider adding 6 to 18 g/acre in a water spray containing gibberellic acid (GA3) followed by up to 30 g/acre in a November water spray. The 2,4-D in the GA3 spray may reduce the GA3-induced leaf and fruit drop and will provide some help with mid- to late-season mature fruit drop. However, the 2,4-D applied with the GA3 early in the season will not provide adequate mid- to late-season control of mature fruit drop in most years.
 
B. VALENCIA ORANGES* 15 g a.e./acre in water spray See comments below
  COMMENTS: If the desired response is to reduce drop of mature fruit and minimize effects on size or quality of next year's fruit, apply when fruit of the following crop is at least 0.5 inch (13 mm) in diameter. May be used as a dual purpose spray in spring for both mature fruit drop control and to improve fruit size of the new crop. See the section on INCREASING FRUIT SIZE. This treatment also reduces fruit stem dieback.
 
C. GRAPEFRUIT*
  (summer fruit drop) 30 g a.e./acre in water spray See comments below
       
  (winter fruit drop) 45 g a.e./acre in hydrated lime spray Oct.–Nov.
    . . . or . . .  
    30 g a.e./acre in water spray Oct.–Jan.
  COMMENTS: If the desired response is to reduce drop of mature fruit and minimize effects on size or quality of next year's fruit, apply when fruit of the following crop is at least 0.75 inch (19 mm) in diameter. May be used as a dual purpose spray in spring for both mature fruit drop control and to improve fruit size of the new crop. See the section on INCREASING FRUIT SIZE. The 45 g/acre treatment applied in hydrated lime (whitewash) is inferior to 30 g/acre applied in water. This is important during long harvest seasons. The preferred winter fruit-drop control treatment is a 30 g/acre water spray applied 3 days before or 3 days after whitewash. January sprays may be somewhat risky, especially when environmental factors favor an earlier-than-usual spring flush of growth. Grapefruit may require special spray application techniques to achieve coverage of interior fruit. These treatments also reduce fruit stem dieback.
 
D. LEMONS* 15 g a.e./acre in water spray Oct.–Dec.
  COMMENTS: Apply a single treatment. Applications to coastal lemons are risky because of their everbearing nature.
 
E. TANGELOS and OTHER
  CITRUS HYBRIDS* 30 g a.e./acre in water spray Sept.–Nov.
  COMMENTS: Apply a single treatment.
 
* 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/gallon. These formulations provide about 1520 g acid equivalent/gal, 12 g acid equivalent/fl oz, 402 g acid equivalent/liter, or 0.402 g acid equivalent/ml. 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. (Added to 500 gal it would be a 16 ppm solution). If spray volumes exceed 500 gal/acre, follow restrictions specified on the label.

[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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