contributed by Dr. Kathleen Willemsen
WSU-Tree Fruit Research & Extension Center

To Control Growth
To Promote Branching
To Promote Bloom To Improve Fruit Quality

To Control Sprouts and Suckers.

Water sprouts can develop on the upper side of main scaffold branches and adjacent to heavy cuts. Root suckers can be a problem around the base of trees. Both types of growth can be controlled by application of either a paint or spray, containing 0.5 to 1.0% NAA. The lower rate has given adequate control of water sprouts and root suckers of apple and pear, but the higher rate is required for control of pear root suckers.

To Control Water Sprouts. NAA should be incorporated in a white interior water base latex paint and applied with a brush. NAA applied without a white paint can result in serious limb and trunk damage from sunburn. Applying NAA as a spray increases the hazard of drift to adjacent and lower branches, spurs and buds, resulting in excessive fruit thinning.

Use a mixture of 5 or 10 fluid ounces of Tre-Hold Sprout Inhibitor A-112 plus 1 quart of white interior water base latex paint and enough water to make 1 gallon of paint mixture. A 0.5% NAA mixture (5 fluid ounces of Tre-Hold Sprout Inhibitor A-112) should be sufficient for most conditions and will control sprouting for 2 to 3 years. Do not use exterior or other than a water base latex paint because of the hazard of paint injury. Do not use less than 25% paint in the mixture. Lower rates give insufficient protection from sunburn.

Brush on the paint mixture around heavy pruning cuts and 3 to 6 inches below the cut to prevent sprouting. Where existing sprouts are to be controlled, remove undesired sprouts and cover the base and up and down the exposed top of limbs and trunk where sunburn is likely and before bud swell in the spring.

Tre-Hold RTU Sprout Inhibitor, a ready-to-use formulation (1.15% Ethyl-1-NAA) is also available to control sprouts and sucker growth on apples and pears. Follow manufacturer's label for use instruction.

Caution: Avoid treating old, weak, or winter-injured limbs with the NAA paint mixture because of the potential of additional injury from reduced sprout growth and sunburn.

To Control Root Suckers. Prune back suckers, but do not treat with chemicals until the end of May (4 weeks after petal fall) to avoid potential excess fruit thinning. Spray suckers thoroughly when they are 4 to 6 inches high and still actively growing. Use a 1% NAA solution, (7.8 gallons of Tre-Hold Sprout Inhibitor A-112 per 100 gallons of spray) and low pressure, 10 to 20 psi, to avoid spray drift.

Control of root suckering may require repeat spray treatment in successive seasons, particularly where root suckering is excessive and has been a problem for many years. Brush on as a paint during the season, before bud break. Cover around major cuts or base of sprouts. Be sure to use interior latex paint to avoid phytotoxicity. For control of root suckers, spray suckers when 4 to 6 inches high and growing rapidly, but not within 4 weeks after petal fall.

Materials Spray conc. Material/100 gallons
NAA (Tre-Hold A-112) + Interior Latex Paint 0.5 to 1.0 percent (25 percent paint) 3.9 to 7.8 gallons + 25 gallons paint
NAA (Tre-Hold A-112) 0.5 to 1.0 percent 3.9 to 7.8 gallons


To Promote Branching

To Promote Side Branching. Young apple trees can be slow to develop side branches and fruiting spurs. As a result, they become leggy and difficult to bring into heavy fruiting. This is particularly a problem with trees on vigorous rootstocks in deep fertile soils.

To promote more lateral bud break, apply Promalin as a foliar spray or spot-apply with a brush using a latex paint mixture. Low rates of foliar applied Promalin should be timed when there are 1 to 3 inches of new terminal growth. For the latex application, high rates are applied in the spring when terminal buds begin to swell but before green tissue emerges.

The response to Promalin will depend on growing conditions, rootstocks, variety and strain. More dwarfing rootstocks and spur types should respond more. Do not apply Promalin on low vigor trees (such as those on M.9 rootstock) or trees under stress from such factors as drought, low fertility or winter injury.

Caution: Do not apply Promalin when air temperatures are lower than 40 F or greater than 90 F. Do not exceed one application per growing season.

APPLES: Non-Bearing Trees

To promote lateral branching: If applying as a foliar spray, apply Promalin at 1 to 3 inches of new terminal growth. Approximately 5 to 10 gallons of spray mixture applied with a pressurized hand sprayer will treat 200 to 300 nonbearing orchard trees 1 to 4 years old. Rate depends on conditions and tree vigor; use higher rates with vigorous trees. Do not use on weak trees, or stunted trees on M.9 rootstock.

If applying Promalin as a latex paint mixture, apply in spring when terminal buds begin to swell but before green tissues emerge. Apply the Promalin-latex paint mixture with a brush or sponge to thoroughly cover the bark surface where growth is desired. APPLY ONLY ON 1-YEAR-OLD WOOD.

NOTE: Do not apply after buds break. Applications after buds have broken may cause some injury to tender shoot tips and fail to promote shoot growth from that point.


To Promote Bloom

To promote bloom the following year: Apply ethephon 4 to 5 weeks after bud break. If some fruit is present, delay application of ethephon 6 weeks after bloom. Avoid double coverage or use on low-vigor trees. Material and rate depend on condition. See general text.


Spray Conc. (ppm A.I.)

Material/100 Gal.

Promalin (foliar application) + Buffer X or nonionic wetting agent (Tween 20; Triton X-100; Glyodin) 125 to 500 ppm + 0.2 to 0.3 percent (1 to 2 pints)
Promalin (latex applied) + Buffer X or nonionic wetting agent (Tween 20; Triton X-100; Glyodin) 5000 to 7500 ppm
+ 0.1 to 0.16 oz. per pint of latex paint
 0.2 to 0.33 pint Promalin per pint of latex paint
Ethephon (Ethrel) + surfactant* 300 to 600 ppm 1 to 2 pints

* Use surfactant according to manufacturer's recommendations, but not more than 1 pint per 100 gallons of spray solution.

To Promote Bloom. Nonbearing trees. Several growth regulators can be used to improve development and fruiting of young apple trees. The selection of material or combination of materials and rates depends on the age and condition of the trees and the desired effect.

Caution: Avoid using ethephon on weak trees or trees on M.9 rootstock because of the hazard of oversetting blossom buds and stunting tree growth.

Bearing trees. Young trees that are slow to bear, or mature trees that produce only a limited number of blossoms in "off years" can be helped by applications of ethephon. Delay applications of ethephon until after the beginning of June drop, about 5 to 6 weeks after bloom, to avoid excess fruit thinning.

Alternate-year bearing on older, mature trees, particularly Golden Delicious, can occur when a high percentage of the spurs blossom in any one season. Although some of these blossoms may not set fruit or are chemically thinned, there may not be adequate return bloom the following season. In this situation, make an application of ethephon the year of heavy bloom. Trees with snowball bloom will require a thorough chemical thinning program plus the use of ethephon sprays.

Caution: Applications of ethephon can reduce fruit size. Early applications of ethephon (before June drop) can cause excess fruit thinning. Use of ethephon on weak trees can cause excess flowering and stunting of growth.

Delay application until June drop begins. Avoid use on low-vigor trees. See text.


Spray Conc.
(ppm, A.I.)

Material/100 gal.


Ethephon + surfactant* 300 ppm 1 pint (3 to 4 pints)

* Use surfactant according to manufacturer's recommendations, but not more than 1 pint per 100 gallons of spray solution.


To Improve Fruit Quality

To Improve Fruit Shape. GA4+7 + BA (Promalin), a growth regulator, can be applied during the bloom period to improve the shape and length of apples, particularly Delicious. Flat apples or a lack of typiness can be the result of: 1) excessively warm or cool weather during bloom or early fruit development; 2) the excessive use of ethephon (Ethrel) in previous years; or 3) use of NAA at a rate of 10 ppm or higher.

Application can be made at any time during the bloom period up to petal fall. However, GA4+7 + BA may be more effective is applied before full bloom during the balloon stage, when wetting of the entire blossom cluster can be achieved. Where poor wetting occurs, use a nonionic wetting agent.

Caution: Fruit thinning can result if GA4+7 + BA is applied to young trees just coming into full bearing. Do not apply more than once per season.


1. To promote longer, typey Red Delicious, apply Promalin when first blossoms are open, but not within 6 hours before or after rain. A spray volume of 100 gallons/acre is recommended. Temperatures between 70 and 80 F give optimum response to Promalin. Can cause excess thinning on young trees.


Spray Conc.
(ppm, A.I.)



Promalin 25 ppm 1.0 pint (1 to 2 pints)

To Control Russeting of Golden Delicious. GA4+7 (ProVide) often reduces the development of physiological russeting in years when russet conditions are present. Physiological russeting is associated with climatic factors such as precipitation, high humidity, and cool temperatures in the early stages of fruit development. Apply GA4+7 (ProVide) as two to four consecutive sprays, beginning at petal fall and continuing at 7- to 10-day intervals. Use of a wetting agent is not recommended. Two sprays of ProVide are often sufficient.

Caution: Do not exceed 40 ounces of ProVide per acre as a total seasonal rate. Avoid application to weak or very young trees. Use of GA4+7 at the higher rate should be accompanied by an aggressive chemical thinning program to avoid reductions in return bloom.

2. To control russeting of Golden Delicious, apply ProVide in no more than 100 gallons of water per acre per application beginning at petal fall and continuing every 7 to 10 days up to 4 applications. Do not exceed 40 ounces per acre per year. See text.


Spray Conc.
(ppm, A.I.)

Material/100 gal.


ProVide 15 to 20 ppm 10 to 13 ounces 10 to 13 ounces


To Improve Fruit Size. Positive responses to Accel applications have been observed on Gala grown under Washington conditions. It is recommended that Accel be applied 2 to 3 times, at 10 to 15 grams active ingredient per acre, starting at petal fall through 10 to 12 mm fruit diameter (about 5 to 10 days between spray applications). Apply in 100 gallons spray solution per acre; thorough coverage, but not to runoff, is adequate. See text.

(PPM, A.I.)
Accel (6-BA) 25-38 ppm 17.8 to 26.7 fl. oz. 10 to 15 g a.i.

Note:  1 bottle Accel = 35.5 fl. oz. = 20 grams a.i. (6-BA)

To Advance Fruit Maturity. To promote more color by advancing fruit maturity, ethephon (Ethrel) can be applied 10 to 21 days before expected harvest. Applications to advance maturity 3 to 5 days can result in smaller fruit size, and can shorten storage and shelf life of fruit not harvested at proper maturity. Ethephon may not promote color when warm weather persists late in the season. Ethephon may not improve color on poor-coloring varieties and standard strains; it is less effective on inside, poorly exposed fruit.

Caution: Ethephon promotes abscission and fruit drop. Use in combination with a preharvest stop-drop spray. Ethephon is not effective for color change on Golden Delicious or advancing maturity of Granny Smith.

Material Spray Conc.
(PPM, A.I.)
Material/100 gal. Material/acre
Ethephon + surfactant* 300 ppm 1 pint (3 to 4 pints)

Washington State University
Tree Fruit Research and Extension Center
1100 N. Western Ave.
Wenatchee WA 98801

phone: 509-663-8181
fax: 509-662-8714

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May 2, 2000