FOLIAR FEEDING and SAR for CITRUS TREES Mongi Zekri and Gary England University of Florida, IFAS
Management practices to improve fertilizer efficiency Evaluation of leaf analysis data Adjustment of rates to the level based on expected fruit yield and IFAS recommendations Selection of fertilizer formulations to match existing conditions
Management practices to improve fertilizer efficiency Proper calibration and maintenance of equipment Careful placement of fertilizer within the root zone or within the canopy Timing to avoid the rainy season (June-early Sept.) Split application and good irrigation management to minimize leaching
Satisfactory nutritional status for citrus leaves Nutrient (%) Nitrogen 2.5-2.8 Phosphorus 0.12-0.17 Potassium 1.2-1.7 Calcium 3.0-5.0 Magnesium 0.3-0.5 Sulfur 0.2-0.4 Nutrient (ppm) Iron 60-120 Boron 36-100 Manganese 25-100 Zinc 25-100 Copper 6-16 Molybdenum 0.1-1.0
http://edis.ifas.ufl.edu/pdffiles /SS/SS47800.pdf SL 253
Benefits of foliar fertilization Foliar fertilization has become important as growers are seeking to improve nutrient use efficiency, reduce losses to leaching and runoff, and fight pests and diseases.
Benefits of foliar fertilization In sandy and calcareous soils, foliar applied fertilizers are 4 to 20 times more effective when compared with soil applied fertilizers. (Lingle & Holmberg, 1956; Wittwer et al. 1959, annual crops, beans, and tomatoes, http://www.ecochem.com/t_foliar. html).
Factors affecting foliar nutrition Response to foliar nutrition is dependent on: Fertilizer form Nutrient concentration Frequency of application Timing (temperature, humidity, wind) Spray volume Spray coverage Leaf age or growth stage
Advantages of foliar feeding When properly conducted, foliar fertilization was found to: increase yield, enhance fruit quality, provide drought tolerance, and improve tolerance to diseases and pests.
http://edis.ifas.ufl.edu/pdffiles/ HS/HS118100.pdf Effects of Mineral Nutrition on Health and Performance of Citrus Trees Arnold Schumann, Tim Spann, Tim Mann, Tom Obreza, and Mongi Zekri Citrus Industry magazine, July 2010, Vol. 91 (7): 22-24.
How does nutrition improve tolerance to pests and diseases? 1. Formation of mechanical barriers, primarily through the development of thicker cell walls. 2. Synthesis of natural defense compounds which provide protection against pathogens.
Advantages of foliar feeding Foliar feeding was found to increase yield from 12 to 25% compared with conventional fertilization. (http://www.ecochem.com/ t_foliar.html.)
Foliar urea or phosphorous acid Foliar applications of lowbiuret urea (25-28 lbs N/acre) or phosphorous acid (2.6 quarts/acre of 26-28% P 2 O 5 ) in late Decearly Jan have been known to increase flowering, fruit set, and fruit yield. (Albrigo 1999, FSHS 112:1-4).
Foliar potassium Postbloom foliar applications of potassium nitrate or mono-potassium phosphate (8 lbs/acre K 2 O) in late April have been found to increase fruit size and yield. (Boman and Hebb 1998, FSHS 111:128-135; Boman 2001, FSHS 114:83-88).
Foliar feeding with micronutrients Considering the wide variations in soil types and ph, foliar sprays of the micronutrients (Mn, Zn, B, and Cu) are a more effective, more economical, and a quicker way to supply these nutrients than soil application (when included with postbloom or summer foliar sprays at about full expansion of the new flush). Sulfate forms are less expensive and nitrate forms appear to facilitate the uptake of micronutrients.
Soil vs. Foliar fertilization There is still a general consensus that foliar fertilization should not be considered a substitute for a sound soil-fertility program. Foliar nutrition can economically supplement a good ground fertilization program. Foliar fertilization can also provide some macronutrient needs and all micronutrients except Fe.
Iron (Fe) Foliar application of Fe is not recommended for citrus trees due to lack of effectiveness and risk of leaf and fruit burn. Soil application of Fe chelates is still the most reliable means of supplying Fe to citrus trees.
Usefulness of foliar feeding Foliar feeding is useful under any condition that decreases the tree s ability to take up nutrients when there is a demand.
When does foliar nutrition make sense? Soil conditions prevent nutrient uptake Small amounts of nutrients are needed which makes ground application inefficient Nutrients are not mobile in the tree Transient deficiency Need nutrients fast Application is profitable
When do soil conditions prevent nutrient uptake? High ph (primarily calcareous soils) makes Mn, Zn, Cu, B and P insoluble and unavailable Low ph reduces availability of Mo and P Excess soil moisture (flooding) Drought Low soil temperature Restricted and damaged root system
Requirements for foliar feeding When no rain is expected for 24 to 48 hours Unlike most pesticides, nutrients need to enter into the leaves ph of spray solution should be 5.5 to 7.5 Spray when wind is minimal Maximize coverage of the underside of leaves (where stomates are located)
Requirements for foliar feeding Spray when weather conditions are humid Spray at 60 to 85 F temperatures Spray fully expanded young leaves of major growth flushes (spring, summer, fall) Most effective foliar feeding is done late in the afternoon or early in the morning (temperature and humidity are right, wind is minimal, and the stomates are open) Addition of a surfactant (and nitrogen source such as urea) may increase absorption
Nutrient uptake after treatment Absorption by underside leaf surface is 20-25 times greater than by the upper surface. Absorption is enhanced by light, even at low levels Heavy rain within 4 hours would reduce potential uptake by half. Rain at 12 hours can reduce uptake by a third. 24% of urea was absorbed in 1 hour. However, only 3% of potassium nitrate (KNO 3 ) was absorbed in 1 hour. (Lea-Cox & Syvertsen, 1995, ASHS, 120: 505-509.)
Tank-mixing foliar nutrients Be careful about possible chemical interactions among foliar fertilizers and other chemicals No nutritional benefit, but phytotoxicity problems can occur using unfamiliar tank mixes Some materials may precipitate, tie up nutrients, and clog nozzles
Tank-mixing foliar nutrients Be sure to read all product labels and do the jar test if uncertain Be consistent in tank mixes, timing, and formulations once you find something that works
Foliar feeding and Systemic Acquired Resistance (SAR) Proponents of foliar feeding consider foliar fertilization an effective means of stimulating the natural defense mechanisms of plants. Systemic Acquired Resistance (SAR) is analogous to the innate immune system found in animals. When a pathogen attacks a plant, the plant reacts to survive. Gene switches are turned on to produce proteins that in some way help the plant to defend itself, resist diseases, and recover.
Systemic Acquired Resistance (SAR) SAR is induced when a plant turns on its defense mechanism in every part of the plant, in response to a chemical or pathogen. There are several commercial chemical sprays that turn on genes in plants, producing Systemic Acquired Resistance (SAR) to diseases. Salicylic acid was found to induce/activate SAR and provide a certain level of disease control.
Some used products Some growers have been experimenting on their own with compounds such as Salicylic Acid, SAver (10% salicylic acid), Actigard, Safeguard, Serenade, Oxidate, Phosphites, Hydrogen Peroxide, KeyPlex, and various fertilizers to reduce the damaging effects of diseases including HLB, to slow down tree decline, and to enhance tree growth and fruit production.
Some products evaluated by Researchers Soil-applied Admire (Imidacloprid), soil-applied Platinum (Thiamethoxam), and soil-applied Actigard (4 applications at 2-month interval) were found to induce SAR and suppress citrus canker, but did not suppress citrus greening (HLB). (Graham, 2010, http://research.fcprac.com)
SAR Facts SAR is not curative or completely disease preventative. Typically, disease prevention by SAR is broad spectrum but incomplete, ranging from 20 to 80% efficacy. Where SAR has shown to work, it only slows down disease progression and reduces disease severity.
SAR Facts & Recommendations SAR alone cannot solve a problem completely. It has to be a component of an integrated comprehensive management program. Data from other crops consistently show that SAR works best at low disease inoculum levels. Thus, SAR management programs should be implemented early in the disease cycle.
Caution for SAR-products If using SAR-induced products, be sure that they are labeled for use on citrus, and that they will not lead to residue issues that may make the fruit unacceptable and unmarketable.
Questions? Is it a good, efficient way to foliar spray nutrients at night?
NO. The stomates are closed at night and nutrients need to enter into the leaves to be useful.
Is it a good, efficient way to foliar feed by air?
NO if the coverage of the lower side of leaves is poor. The stomates in citrus are located on the lower side of the leaves and nutrients need to enter into the leaves to be useful.
Is it a good, efficient way to foliar feed with solutions that have a ph lower than 5 or higher than 7.5?
NO. Leaf absorption of nutrients is poor. The solution may cause leaf and fruit burn. At high or low ph, some fertilizer materials may precipitate, tie up nutrients, and clog nozzles.
YOUR Questions?