[1] Functional Characteristics
Naphthaleneacetic acid (sodium salt), belonging to the auxin class of plant growth regulators, possesses the basic functions of general auxins. Additionally, it promotes the formation of adventitious and lateral roots in plants. It is used to stimulate root development in seeds, rooting of cuttings, and the formation of fibrous roots in solanaceous crops. It accelerates the rapid enlargement of fruits, tubers, and rhizomes, hence it can be used as a swelling agent in vegetables and fruit trees. It improves flowering and fruit setting rates, prevents flower and fruit drop, and has an anti-drop function. Not only does it increase yield and improve quality, promoting lush foliage and robust plant growth, but it also effectively enhances crop resistance to drought, cold, waterlogging, disease, saline-alkali stress, and other adverse conditions.
[2] Application Techniques
a. Promoting Adventitious and Lateral Root Formation
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Ginkgo (Ginkgo biloba) cuttings: Dip cuttings for 10 seconds in 600 mg/L NAA solution to promote rooting and increase survival rate.
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Virginia Creeper (Parthenocissus quinquefolia) cuttings: Dip cuttings for 10 seconds in 1000-2000 mg/L NAA solution to improve rooting rate and root number, promoting survival.
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Shrubby Cinquefoil (Potentilla fruticosa): Soak hardwood or softwood cuttings in 500 mg/L NAA for 2 hours to significantly increase rooting rate.
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Purpleleaf Japanese Barberry (Berberis thunbergii ‘Atropurpurea’) softwood cuttings: Dip cuttings for 10 seconds in 500 mg/L NAA solution to increase rooting rate to 94.2%.
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Fortunella spp. (Kumquat) branches: Treat branches with 80-100 mg/L NAA solution to promote rooting in hydroponic cuttings.
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Osmanthus fragrans (Sweet Olive): During full-sunlight mist propagation of softwood cuttings, soak cuttings in 200 mg/L NAA for 60 minutes. With water supply: Start misting after insertion (30s spray / 2min interval). Callus appears in the 2nd week. Then mist 30s / 30min interval. Rooting occurs in weeks 3-4; mist 30s / 2h interval. This greatly improves rooting rate.
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Red Twig Dogwood (Cornus sericea) cuttings: Soak cuttings in 100 mg/L NAA for 2 hours to promote rooting rate and increase root number.
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Bauhinia × blakeana (Hong Kong Orchid Tree) cuttings: Dip cuttings for 5-10 seconds in 150 mg/L Sodium Nitrophenolate + 600 mg/L NAA solution to significantly enhance rooting.
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Bamboo Willow (Salix spp.) softwood cuttings: Soak cuttings in 120 mg/L NAA solution for 45 minutes to improve sprouting and rooting rates.
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Grape (Vitis vinifera) cuttings: Before insertion, soak cuttings in 100-200 mg/L solution for 6-12 hours to promote rooting, faster sprouting, and robust plant development.
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Tree transplantation: Soak the base for 24 hours in 50-100 mg/L solution; or dip the base for 3 seconds in 1000-2000 mg/L solution to promote rooting and increase survival rate.
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Tea (Camellia sinensis), Mulberry (Morus spp.), Metasequoia (Metasequoia glyptostroboides), etc.: Soak the base of cuttings for 24 hours in 10-15 mg/L solution; or soak the base for 3-4 hours in 60-100 mg/L solution to promote rooting.
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Mongolian Oak (Quercus mongolica) seeds: Soak seeds in 150 mg/L NAA for 12 hours to significantly affect seedling growth, increasing seedling height, ground diameter, main root length, and number of lateral roots.
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Phoebe bournei (Min Nan) cuttings: Soak cuttings in 100-600 mg/L NAA solution for 6 hours to improve rooting rate.
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Hickory (Carya spp.) cuttings: Soak the base of cuttings in 500 mg/L NAA solution for 6 hours to significantly increase rooting rate and root number.
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Sweet Potato (Ipomoea batatas): Soak the base (3-4 cm deep) of prepared slips in 10-20 mg/L solution for 6 hours before transplanting; or dip slips for 3 seconds in 80-100 mg/L solution and plant immediately. This improves survival rate, enlarges tubers, and increases yield.
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Cucumber (Cucumis sativus) seeds: Soak seeds in 10 mg/L solution for 12 hours, rinse 1-2 times with clean water, dry, then sow to promote rooting, germination, and produce strong, uniform seedlings.
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Radish (Raphanus sativus), Chinese Cabbage (Brassica rapa pekinensis) seeds: Soak seeds in 15-30 mg/L solution for 12 hours, rinse 1-2 times with clean water, dry, then sow to promote rooting, germination, and produce strong, uniform seedlings.
b. Promoting Grain and Fruit Development, Increasing Yield
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Wheat (Triticum aestivum): Soak seeds in 10-20 mg/L solution for 12 hours, rinse 1-2 times, dry, then sow; Spray flag leaves and panicles with 15-30 mg/L solution 20-30 days after transplanting to promote tillering, increase seed setting rate, spikelet number, and 1000-grain weight, boosting yield. Also improves plant resistance to saline-alkali soil and dry hot wind.
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Rice (Oryza sativa): Soak seeds in 10-20 mg/L solution for 6 hours before transplanting; Spray flag leaves and panicles with 10-20 mg/L solution to promote green recovery, strengthen plants, and increase yield. Can also be used in seedling beds: foliar spray with 5-10 mg/L solution to promote root development.
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Corn (Zea mays), Millet (Setaria italica): Soak seeds in 20-30 mg/L solution for 12 hours, rinse 1-2 times, dry, then sow; Foliar spray with 15-20 mg/L solution during growth period to promote growth and increase yield.
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Cotton (Gossypium hirsutum): Foliar spray once with 5-7.5 mg/L solution during full bloom to prevent bud and boll shedding, enlarge bolls, improve quality, and increase yield.
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Tomato (Solanum lycopersicum), Eggplant (Solanum melongena): Start foliar spraying with 5-10 mg/L solution before plant establishment and at flowering, every 10-15 days for a total of 3 times, to promote growth and increase yield.
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Cucumber (Cucumis sativus): Foliar spray the whole plant 1-2 times with 5-10 mg/L solution during growth to increase female flower density and regulate growth.
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Pepper (Capsicum annuum): Spray flowers with 20-50 mg/L solution during flowering to prevent flower drop and promote fruit setting. Yield increased by 13.4% compared to control. Promotes growth and accelerates maturity.
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Legumes: Soak seeds in 10-20 mg/L solution for 0.5-1 hour before sowing; Foliar spray 2-3 times with 5 mg/L solution during growth to increase yield.
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Potato (Solanum tuberosum): Soak tubers in 10-20 mg/L solution for 12-24 hours to promote sprouting.
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Pineapple (Ananas comosus): Spray leaf buds and flower buds with 10 mg/L solution before flowering; Spray young fruits 2-3 times with 20 mg/L solution during fruit development; Inject 30 mL of 15-20 mg/L solution into the plant heart during late vegetative growth phase.
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Sugarcane (Saccharum officinarum): Foliar spray 2-3 times with 15-20 mg/L solution during tillering to promote growth and increase yield.
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Lemon (Citrus limon): Spray the tree canopy with 100-200 mg/L solution shortly before fruit ripening to accelerate ripening and increase yield.
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Tobacco (Nicotiana tabacum): Foliar spray 2-3 times with 10-20 mg/L solution during growth to regulate plant growth and improve leaf quality.
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Angelica dahurica (Bai Zhi): Treat seeds with 0.5-1 mg/L solution to promote seedling growth, leaf length and width, and plant height.
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Citrus (Citrus spp.): Spray the fruit-bearing parts with 40-60 mg/L solution 15 days before harvest to prevent pre-harvest fruit drop and increase yield.
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Apple (Malus domestica), Pear (Pyrus spp.), Jujube (Ziziphus jujuba): Starting 45 days before harvest, foliar spray the whole plant with 15-20 mg/L solution every 15 days to promote growth, prevent pre-harvest drop, and increase yield.
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Watermelon (Citrullus lanatus): Dip or spray flowers with 20-30 mg/L solution when female flowers first open to improve fruit setting rate.
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Pumpkin (Cucurbita spp.): Apply 5-20 mg/L solution to the ovary during flowering to improve fruit setting rate.
c. Flower and Fruit Thinning
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Apple ‘Golden Delicious’: Spray with 20 mg/L NAA 14 days after full bloom reduces fruit set by 40.5% per 100 clusters compared to control. Generally, for NAA thinning in apples: early-maturing varieties should be sprayed within 10 days after full bloom; effective thinning period for mid/late-season varieties is 10-15 days. Concentration depends on cultivar: Spray 5-10 mg/L NAA for ‘Early McIntosh’, ‘Jonathan’, ‘McIntosh’, ‘Red Delicious’, ‘Wealthy’, etc. Spray ‘Golden Delicious’ with 10-20 mg/L. For strongly biennial bearing varieties like ‘Stayman’, use 15-20 mg/L.
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Note: Do not use NAA as a thinner for ‘Delicious’ and ‘Starking’ apples, as it may inhibit young fruit growth, resulting in small, unmarketable fruit. For early varieties, spraying is best at petal fall; spraying 10 days after full bloom can easily cause under-ripe, early-maturing, and split fruit. Avoid using thinners in orchards affected by frost, poor soil drainage, nitrogen deficiency, or high-density planting causing insufficient light.
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Peach (Prunus persica): Spray with 40-60 mg/L NAA solution 20-45 days after flowering to effectively thin excess fruit and control fruit load.
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Pear (Pyrus spp.), Satsuma Mandarin (Citrus unshiu): Spray once with 100-300 mg/L solution during flowering to effectively thin excess fruit and control fruit load.
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Persimmon (Diospyros kaki): Spray with 5-10 mg/L NAA solution 10 days after flowering to thin excess fruit and control fruit load.
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Plum (Prunus salicina), Apricot (Prunus armeniaca): Spray once with 20-30 mg/L NAA 1-2 days during full bloom to effectively thin flowers and improve fruit quality.
[3] Precautions
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NAA is difficult to dissolve in cold water. When preparing the solution, first dissolve it in a small amount of alcohol, then dilute with water; or first add a small amount of water to make a paste, then add sufficient water, followed by adding sodium bicarbonate (baking soda) and stirring until completely dissolved.
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Using NAA for thinning flowers/fruits in early-maturing apple varieties can easily cause phytotoxicity. Using 40 mg/L NAA on ‘Qiubai’ pear can cause damage; excessive concentrations can cause deformities, leaf scorch, and abscission. Concentrations above 50 mg/L NAA can cause phytotoxicity in fig; excessive rates on watermelon and melon can easily cause phytotoxicity.
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Naphthaleneacetic acid (NAA) can cause poisoning if ingested, potentially leading to liver and kidney damage. There is no specific antidote. If poisoning symptoms occur, seek immediate medical attention.
