Agriculture: Citrus Pest Management Guidelines

Fruit Thinning with Naphthalene Acetic Acid (NAA)

Success with NAA as a fruit-thinning agent requires excellent coverage and wetting; low-volume applications are not known to be effective. Be sure to use the formulation of NAA registered specifically for fruit-thinning; a different formulation is registered for sucker control.

Variety Amount to use REI‡ Application timing
    (hours)  
Always read the label of the product being used.
 
A. ORANGES, TANGERINES (MANDARINS), TANGELOS, and TANGORS 100–500 mg/liter
(100–500 ppm)
24 When fruitlets are 3/16–3/4 inch
(5–20 mm) diameter
COMMENTS: Do not apply within 150 days of harvest. Make only one application per year. Within the specified concentration range, inadequate to excessive thinning may occur. In general, inadequate thinning occurs from the lowest label rate when maximum daytime temperatures on the day of application and several days thereafter are relatively low (~85ºF [29ºC]). Excessive thinning generally occurs from the highest label rate when maximum daytime temperatures on the day of application and several days thereafter are relatively high (~100ºF [38ºC]). In addition, excessive thinning can occur when NAA is applied to unhealthy or water-stressed trees. Do not use on varieties where both young fruit and fruit close to maturity are present on the tree. Use either the ammonium salt or the potassium salt formulation of NAA.
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