Avocado: Preventive treatments against fruit drop

History and Evolution of the Avocado

Avocados have been part of the Mesoamerican diet for approximately 8000 years. It is believed that avocados began to be cultivated for human consumption around 5000 years ago, with the Persea americana.

The word avocado comes from the language Nahuatl, where the word "ahuacatl" means testicle and refers to the shape of the fruit. This explains why it was also called the "fruit of fertility," as the Aztecs believed it had special powers, including aphrodisiac qualities for men and women, as well as giving strength to those who consumed it.

The honor of making the first technical description of the avocado went to Francisco Hernández in his “History of the plants of New Spain"after having carried out the first exploration in Mexican territory from 1571 to 1576.

The first mention of the word avocado (English) was in 1696 by Henry Sloane, who would also describe her as the “alligator pear"since the rough appearance of its skin allowed it to be compared to the skin of this reptile.

The conquistadors must have brought the avocado to Spain around 1600, as there are records of the tree in the Valencia Botanical Garden and of some plantations in the province of Málaga in 1770. Likewise, Indian traders and wealthy families brought avocado trees to Spain in the XNUMXth and XNUMXth centuries to provide shade for their gardens. Later, avocado trees began to spread worldwide. 

The avocado was described by the horticulturist y botanical British Philip Miller and published in “The Gardeners Dictionary” in 1768 in its eighth edition, using the name Persea, designated by Theophrastus, who derives from the Greek in honor of Perseus, the demigod, to refer it to a tree of the East, and Blazer to mention its origin in the American continent.

In 1924 it began to be implemented in Malaga, at the Southern Agricultural Station, where the initial project discussed the introduction of exotic fruit trees. It was when the Torrox experimental station was incorporated that an initial avocado seedbed was established around the 30s.

The popular Hass variety first saw the light of day in 1926, and the first avocado tree died of old age and rotten roots around 2002. It was a mere lucky discovery. In those years, the most popular avocado variety was the Fuerte, and this was the variety that Rudolph Hass He intended to grow from seed, trying to graft his plant with several types of avocados, but none of them yielded the desired results. Disappointed, he considered cutting down his tree, but his children convinced him not to, as they preferred the flavor of his fruit to the popular Fuerte. Thanks to this, we now have this avocado variety with a creamier taste.

There are currently more than 400 varieties of avocado. It is considered one of the more nutritious fruits, with high content in fiberPlus potassium that bananas and rich in folic acid y Vitamin E. It is also one of the fruits with the highest protein content, and its oils are good for the skin, as they have Antioxidants that prevent aging.

Requirements for avocado cultivation

Before establishing an avocado plantation, you must know its characteristics. requirements edaphoclimatic, and check that the characteristics of our plot are adequate to such requirements, this being indispensable condition so that the crop is profitable.

The avocado in its origins evolved into Andisols soils, characterized by presenting Low apparent density, high macroporosity, high organic matter content and high rainfallFor this reason, avocados grow best in soils with high hydraulic conductivity, with shallow roots, no absorbent hairs, and very sensitive to a lack of oxygen.

Avocado crop humidity

Periods of heat and drought can cause fruit to drop., especially in mountain varieties. Excessively wet sites are not suitable, due to the increased likelihood of certain soil-borne diseases, to which the species is highly susceptible.

Lighting in avocado cultivation

Avocado cultivation requires a good and direct sun exposureShaded branches are unproductive. Pruning to allow sunlight to reach the interior of the canopy is highly recommended. Only the main branches and trunk should be shaded.

Soil in avocado cultivation

It adapts to a wide variety of soils, from sandy to clayey, volcanic silt, lateritic and limestone, but grows best in loamy, well-drained, slightly acidic soils rich in organic matterThe Antillean variety tolerates calcareous and slightly saline soils. None of the varieties tolerate heavy, poorly drained soils, and should not be planted where the water table is less than 1 m below the surface. The optimal pH range is considered to be between 5,5 and 7, although some cultivars grow well in soils with a pH of 7,2 to 8,3.

Water requirements for avocado cultivation

El irrigation It is, without a doubt, the most determining factor in the success or failure of our avocado. Especially in the early stages of life. It requires high rainfall rates, but well distributed over time and with slow emission. sensitive to fungus Phytophthora cinnamoni y Rosellinia necatrix, whose development is favored by excess humidity, aeration and poor drainage.

The amount of irrigation water depends greatly on the climate, rainfall, soil type and composition, varieties, etc. For commercial productions in Spain there are average values ​​already established for localized drip irrigation, with irrigation rates by month, etc., but always subject to multiple variations due to the other soil and climate factors already mentioned. The best option is localized irrigation because:

• It is slow emitting.
• It is easier to regulate the amount emitted by the dropper.
• Since irrigation is variable depending on age, we can better calculate irrigation doses.
• It is easy to program.
• The irrigation dose will increase over the years and it will be easier to establish frequencies and times.

Recommendations for avocado cultivation in the southern and eastern climate zones of Spain.

These data are indicative. According to the FAO, water volumes of 4000 m³/ha/year would be sufficient for avocado cultivation, while other publications recommend irrigation doses calculated according to climatic data found by a meteorological station that show irrigation needs of approximately 3500 m³/ha/year.

On the other hand, we must also take into consideration the water quality, since the avocado does not tolerate irrigation with water with electrical conductivity above 1,5 mmhos/cm.

Nutrition in avocado cultivation

It's important to note that the nitrogen, phosphorus, and potassium requirements for trees younger than 3 years old are 1:2:1; for slightly older trees just beginning to produce, the ratio is 1:1:1; and for mature trees in full production, the ratio is 2:1:2.

In avocado nutrition, we must primarily consider the needs for nitrogen, phosphorus, potassium, calcium, magnesium, zinc, boron, and iron, among other essential nutrients.

• Nitrogen: The requirements for this element are estimated at 100–200 UF per hectare per year, with the highest requirements occurring between May and October. Given the high mobility of this element and to avoid leaching losses that result in the contamination of aquifers, applications should be made in small quantities along with irrigation water.
• Phosphorus: The requirement for this element is estimated at 20–40 UF per hectare per year. Additions should be made during flowering and at the beginning of root development.
• Potassium: The requirement for this element is estimated at 100–200 UF per hectare per year. Maintaining an adequate level is important to ensure fruit growth, and it should be supplied between May and October.
• Football: The requirement for this element is estimated at 30-50 UF per hectare per year. The greatest absorption of Ca by avocado occurs in the early stages of fruit development.
• Magnesium: The needs of this element are estimated at 10-30 UF per ha per year.
• Zinc: Requirements are estimated at 10-30 UF per hectare per year. Soils with high pH levels are often deficient in this element.
• Boron: The requirement for this element is estimated at 3-5 UF per hectare per year. It is very important for fruit setting and is well assimilated by the inflorescences.
• IronThe peculiarity of this element lies in the fact that it solubilises in acidic media and precipitates in basic media, making it difficult to supply plants. Chelates, by sequestering the metallic iron ion, form stable, soluble molecules that are easily assimilated by the plant. Therefore, iron applications to plants should be carried out in the form of chelates.

El distribution of each element throughout the crop cycle, will depend on the role it plays in the plant's development. Nitrogen requirements are highest during vegetative growth, while potassium and phosphorus are most important during flowering and fruiting. Calcium is essential during fruit development, and boron during flowering, given its influence on pollen viability.

To establish an adequate fertilization plan, it is important and basic to consider a soil, foliar and irrigation water analysis, as this allows us to use the appropriate products to correct a critical level or nutritional deficiency in a timely manner. Fertilization should be carried out through monthly fertilization programs, taking into account the phenological phase of the crop, and paying special attention to nitrogen contributions, since an excess of this element can cause the fall of flowers and fruits.

La organic matter is a very important factor as a complement to chemical fertilization, so sufficient amounts should be applied according to the age or size of the tree. It is important to maintain or restore soil fertility for a stable plantation.

To summarize, for proper avocado nutrition you should:

1. Maintain an oxygenated, fertile soil rich in organic matter.
2. Define the expected extractions from our crop.
3. Discount some of the nutrients supplied by water, taking into account the interactions between them, and adjust based on soil reserves.
4. Choosing the optimal application times.
5. Verify and correct with foliar analysis

Causes of fruit drop in avocado cultivation

Serving solely and exclusively to the phenological stages between fruit setting and initial growth and the start of vegetative activity of the shootsThere are four main causes that can directly or indirectly cause avocado fruit to fall:

1.Nature

Avocado cultivars can produce thousands of inflorescences, each of which, in turn, may be made up of more than 100 flowers, so the total number of flowers per tree can be more than a million.

Avocado fruits that do not set are divided into two groups, those coming from pollinated flowers, but in which fertilization was not achieved, and from pollinated and fertilized flowers that give rise to a normal, seeded embryo.

Under favorable conditions, avocados More fruit sets than the tree is capable of carrying to maturity. Under these conditions, the plant adjusts its ability to nourish the fruits by modifying their number, that is, causing the massive fall of newly set fruit during the first three to four weeks and again in the summer, when the fruit has already reached between 10% and 40% of its final size.

Some studies show that during the first week after anthesis, 80% of the fallen fruits came from pollinated but unfertilized flowers. However, one month after anthesis, all the fallen fruits had been fertilized and showed normal embryo and endosperm development.

A final drop can occur in autumn, as a result of insufficient water supply and rising ambient temperatures.

2. Physiological

This cause is based on the fact that the plant suffers from conditions of Stress that hinder their normal physiological functioning, that is, when faced with a excess temperature above 35º C or a water deficit, the plant will respond at a physiological level by altering its normal functioning. One of these responses may be a abnormal stomatal behavior which causes excessive transpiration in the plant and, therefore, excessive water loss, or on the contrary, the plant completely closes the stomata, producing an inhibition of photosynthesis and carbohydrate transport. In both cases, a possible fruit fall It would be related to these abiotic stresses, on the one hand linked to excessive temperature or sun exposure and, on the other hand, to a water deficit, due to excessive loss of water through transpiration or a low irrigation supply.

There are three possible solutions to prevent this accident.

a) Plant avocado in an area with climatic characteristics suitable for its cultivation.

b) High-altitude sprayingUsing droplet sprinklers, which reach the surface of the tree's leaves so that the water evaporates, through heat exchange with the leaf surface, cooling the leaves. This method requires a higher initial investment and extraordinary water expenditure, although it has the advantage that it can be incorporated into fertilizer treatments and also used in preventive measures against low temperatures.

c) From the technical and R&D department of Cultifort, we recommend a nutritional solution with one of our Special Products, CultisilK. It is a potassium silicate that also incorporates free amino acids. On the one hand, the silicon will create a protective layer on the plant to cushion the thermal regime In the face of excess temperature, on the other hand, potassium will act as regulator of good stomatal behavior, also helping to maintain cellular turgor and thus avoiding excessive water loss through transpiration; and finally, free amino acids are focused on reinforcing the synthesis of chlorophyll activate photosynthesis, avoiding interruption in the synthesis of assimilates and ensuring that the competitive relationships between the fruits and the growing shoots are not accentuated.

Another possible cause of stress is root asphyxia. Remember that avocado crops are extremely sensitive to excess soil moisture. Root asphyxiation occurs either due to poor irrigation management or excessive rainfall during a time of lower water demand. In any case, there is a period of approximately 90–100 days after flowering and fruit set in which this crop is especially sensitive to excess moisture, and can suffer root asphyxiation stress, leading to a massive fall of fruits directlyTo avoid such situations as much as possible, it is recommended to plant avocados in loose soils with a macropore volume greater than 17% (24% is ideal), of good drainage, with a minimum depth, planning well the water outlets of the plot avoiding accumulations in the lowest parts and carrying out a good irrigation management, optimizing water contributions and soil oxygenation.

In relation to soil oxygenation, at Cultifort we have developed Oxifort, another of our Special Products. It is a product that, when applied together with irrigation water, releases oxygen slowly, improving aeration in the root zone, It prevents root asphyxiation and the development of anaerobic microorganisms. It also improves soil structure, making it more spongy and allowing air and water to circulate better through the pore space. It increases fertilization efficiency, especially nitrogen, and promotes the development of beneficial microorganisms involved in the transformation and mobilization of soil nutrients. 

3. Nutritious

An fruit drop from a nutritional point of view, could have its origin in a limited supply of assimilates or in strong competition for nutrients between fruits and vigorous shoots that develop at the same time.

conduct a correct fertilization program It is essential, as this practice represents an expense for the farmer and can negatively impact the environment if not done correctly. The current approach to managing avocado fertilization is oriented towards providing fertilizers in specific times and quantities for each phenological state, based on the nutritional requirements of avocados to sustain a given production level. This aims to increase yields without unnecessarily increasing production costs.

When the content of these elements is deficient, a series of symptoms often appear in the plant. Visually, this can help us identify which element is below its optimal content. However, Determining deficiencies through visual symptoms is not a solid tool for establishing a firm diagnosis.. A multitude of causes (phytotoxic effects of phytosanitary treatments, attacks by fungi, bacteria and pests, damage caused by adverse weather conditions, toxicities, etc.) can generate symptoms in the tree similar to those caused by deficiencies and lead to a misdiagnosis. Likewise, deficiencies in certain elements may occur that are not reflected in the appearance of symptoms, or the characteristics of the plot itself (organic matter content, soil pH, etc.) as well as its management (excessive application of soil enhancers or fertilizers, earthworks, etc.) may be the determining factors in the low availability of these elements for the plant. However, excesses in the content of essential elements can also negatively impact the crop, generating toxicity problems and other undesirable situations.

Improving Fruit Retention in Avocados: Tips for Easier Reading

Avocado flowers require more than just nutrient reserves to develop into fruit. However, massive flower and fruit drop can limit retention. Only about 1% of the fruit remain on the tree. Although factors such as extreme temperatures and insufficient pollination have been suggested, we still don't fully understand why some flowers are retained and others drop prematurely.

Connection between Nutritional Status and Curdling: There is a direct connection between the starch content of flowers and their ability to develop into fruit. Flowers with higher starch content are more likely to develop fruit. However, most avocado flowers have a low starch content, reducing their chances of fruit development.

Importance of Sugars in Development: During the process of photosynthesis, the plant synthesizes glucose, which is essential for nutrient assimilation and efficient transport. During fruiting, the fruits accumulate most of the exported sugars.

Cultifort Specific Products for Avocado: Cultifort offers products such as AMACOL and BVC EVOLUTION (formerly BVC 2021), rich in reducing sugars. AMACOL, a biostimulant with amino acids, provides energy and promotes absorption. BVC 2021 acts as a leading biostimulant, optimizing flowering, promoting fruit set, and improving vegetative development and final yield with amino acids, nitrogen, potassium, and seaweed.

The role of the nitrogen It plays a role in promoting vigor in the growth of shoots and fruits. However, excessive vigor can inhibit the development of flower buds in autumn, reduce the setting of new fruits in spring, and reduce the quality of the harvested fruit. A deficiency of this element will lead to a weakening of the tree, causing a decrease in production, while an excess of nitrogen could reverse the tree's tendency toward greater vegetative than reproductive growth, causing a direct fall of fruits.

El match Phosphorus is an important nutrient associated with the processes of chemical energy transport during photosynthesis for carbohydrate production. These molecules are subsequently required during flowering and to increase oil accumulation in the fruit. Phosphorus also plays an important role in the formation of cell membranes that regulate the movement of water and other nutrients between the cells of shoots, flowers, and fruits. Phosphorus availability is known to be strongly associated with root development and determined by soil pH.

El potassium Potassium is a mineral element that contributes to the water transport processes within the cells of the tree and its fruits, thus playing an important role in the vigorous growth of roots, shoots, and fruits. Specifically, potassium facilitates the transport of carbohydrates to the growing roots and fruits, essential for adequate accumulation of dry matter for a high yield of marketable-sized fruits. It is also important in the plant's protection mechanisms against frost or drought conditions, regulating the stomatal behavior of the leaves. A deficiency of this nutrient can cause poor stomatal behavior, with the associated problems we have previously discussed regarding the opening and closing of stomata. Cultifort offers different solutions within its catalog to prevent possible potassium deficiencies, among which we highlight: Cultifort K or its pH neutral version, Cultineutral K.

However, to meet the NPK needs of both newly planted trees and avocados in full production, Cultifort provides several alternatives:

• Cultifort Soluble 11-24-11 for newly planted trees.
• Macrofol Green Plus (18-18-18+2Mg+ME) for avocados that are going into production.
• Cultifort Special Avocado (16-8-20) for adult plantations in full production.

El Calcium It is the most demanded macronutrient by avocado after nitrogen, phosphorus and potassium. It is a nutrient of low mobility in the plant, without a specific absorption mechanism and that moves via the xylem by simple perspiration. Because of this, a potassium deficiency that reduces perspiration could also cause a calcium deficiency. Calcium is required by growing fruits and apical meristems due to the synthesis of auxins in these growing areas. Therefore, as the fruits grow and stop synthesizing auxins, calcium is no longer important for them. That is, The greatest demand for calcium by avocado occurs during the period in which the fruits are growing, especially during the first months after fruit set. In other words, all the calcium contained in the fruit is accumulated during the first five months of initial development. This is because calcium is only mobilized to actively growing cells, as occurs during the initial development of the seed. For this reason, the new shoots developed in spring compete strongly for this nutrient, reducing its availability for the newly growing fruits.

To prevent a possible deficiency of this important nutrient, we recommend the application of Cultifort CalciumThis is a liquid formulation of calcium complexed with lignosulfonic acid to improve its absorption, along with carbohydrates and organic polyacids to enhance its mobility within the plant. Cultifort Calcium It does not provide nitrogen, so calcium is distributed throughout the plant more evenly, reinforcing cell walls in roots, stems, leaves and growing fruits, preventing them from falling (peduncle) and improving their firmness.

El Magnesium It is a structural macronutrient. It forms the nucleus of the molecule clorofila, so it is directly linked to the net assimilation rate of CO₂ o photosynthesisA deficiency in this nutrient causes chlorosis in the basal or older leaves of the tree's branches, causing them to lose some of their photosynthetic potential and, therefore, reduce the synthesis of photoassimilates, which can accentuate the competitive relationships between growing fruits and new shoots. Our solution for a deficiency in this nutrient is Cultifort Mg.

El sulfur It is a multifunctional element related to the synthesis of sulfur-containing amino acids (methionine and cysteine) and the formation of proteins. It also plays a role in the synthesis of vitamins and phytohormones and is also important in the formation of cell membranes (sulfolipids).

El boron It is another multifunctional element, in this case, a micronutrient. Its relationship with pollen production and pollen tube germination is well known, but it is also an element that participates in the transport of sugars, carbohydrates, and potassium, in nitrogen metabolism, protein formation, and hormonal regulation. Boron accumulates most rapidly during the second season of fruit growth. This is important because boron is required early in spring to support pollen tube development, at a time when the growing older fruit is placing a high demand on it. Therefore, in years of high fruit load, it is useful to increase the boron dose proportionally to the expected harvest. Cultiboro Plus It is our recommendation to avoid deficiencies of this nutrient.

El iron It is an enzyme activator, a micronutrient precursor to the chlorophyll molecule, and present in cytochromes, which are important in photosynthesis and plant respiration. Its deficiency manifests itself as chlorosis in young shoots or leaves, resulting in a loss of photosynthetic efficiency. Ferrofort, is Cultifort's alternative to prevent deficiencies iron.

Manganese y zinc, are also enzyme-activating micronutrients. The first is related to carbohydrate and fatty acid metabolism, the Krebs cycle, and photosynthesis, and the second is related to auxin synthesis. Their deficiency is associated with a decrease in photosynthesis and poor growth in the case of zinc. Cultifort's solution for preventing zinc and manganese deficiencies is Manzifort.

Due to the nutrient competition between shoot growth, flower buds, fruits from the previous season, and newly set fruits, avocados need to produce sufficient carbohydrates and provide the necessary amounts of nutrients for the requirements of each phenological stage. If these carbohydrates are not sufficient, the fruit normally becomes dehydrated. a natural fall of set fruit, a reduced growth of vigorous and non-vigorous shoots required to form flower buds in summer, a significant decrease in yield or a reduction in fruit size, which is usually determined during the first 3 months after fruit set.

4. Pathogens

The pathogens responsible for possible fruit drop in avocado are related to root rot that weaken the plant.

In this case, we are going to differentiate between two pathogens, two soil fungi that cause root rot in avocados: Phytophthora cinnamomi Rands. and Rosellinia necatrix Prill.

Phytophthora cinnamomi It is classified as an Oomycete fungus.

The disease manifests itself in the field with a progressive decline of the tree, presenting a general appearance of wilting. leaves are smaller of the normal color pale green to yellow and often wilted. The defoliation The infection of the tree begins at the top and progresses downwards, and in highly developed stages of the infection all the leaves are lost, the branches drying out and burning due to the direct action of the sun due to the absence of foliage. Fruiting is declining In a very advanced stage of the disease, the tree dies. The appearance of aerial symptoms is a direct effect of the rotting of most of the small feeding roots (1 to 3 mm in diameter), which appear blackened, brittle, and dead, and are difficult to find in severely affected trees.

Infection by the pathogen is optimal at soil temperatures between 21 and 30°C, and infection is virtually non-existent above 33°C or below 9-12°C. The optimal pH for disease development is 6,5.

La prevention The prevention of root rot includes the production and distribution of healthy nursery plants and preventing the spread of the pathogen in established plantations. To obtain healthy nursery plants, seeds that are completely free of contamination must be used. Infected seeds can be controlled by immersion in hot water at 49°C for 30 minutes. The use of a substrate free of the fungus, planting in an area with no incidence of the fungus, and using irrigation water that does not come from infected areas are recommended prevention methods against this fungus. Likewise, locating and isolating potential sources of infection is essential to prevent the spread of the disease.

Just like chemical control For the disease, foliar applications or trunk injections of phosphorus acid buffered with potassium hydroxide or aluminum ethyl phosphite are quite effective and can recover diseased trees. To maintain a low level of inoculum of Phytophthora cinnamomi In established plantation soils, solarization treatments are recommended by applying a transparent plastic cover to the soil for at least six weeks during the summer. The use of avocado rootstocks (Duke7, Dusa, etc.) tolerant to this pathogen can also be used in replanting dead trees and in new plantations suspected of being infested by the pathogen.

Rosellinia necatrix It is classified as an Ascomycete fungus.

Air symptoms show a progressive weakening of the plant, accompanied by a loss of vigor. The leaves wither and dry up, and the tree may eventually die. The fungus mycelium can be observed on the neck and on the surface, beneath the bark of the roots.

Rosellinia necatrix It is able to survive for years in the soil, which is why control measures should be preventative rather than curative. Some studies recommend a integrated control This involves the use of tolerant rootstocks, the removal and burning of infected plants, and physical measures such as solarization. Both biological and chemical control in the field are still under development, although the use of Trichodermas appears to be yielding good results. Likewise, the proliferation of antagonistic organisms may be an interesting alternative for preventing this fungus.

The incidence of these fungi does not cause a direct fall of fruits, but as a consequence of the symptoms produced and in a manner hint, yes, abscission of avocados could happen.

El Cultifort's technical and R&D department, recommends a series of alternatives aimed at preventing these diseases:

1. On the one hand, avoid planting in heavy or poorly drained soils, conditions that favor the development of these fungi.
2. Microvital – LIt is a biological soil activator of plant origin, rich in Magnesium, micronutrients, organic compounds and flavonoid molecules, aimed at improving the physical-chemical characteristics of the soil and the microbiota activation.
3. Foliquino. Formulated with aluminum lignosulfonate with systemic and phytofortifying action, which increases the synthesis of metabolites in the plant, such as polyphenols and phytoalexins. Its action is mainly focused on the prevention of Phytophthora cinnamomi in pre-flowering and flowering stages, as it also improves the tree's covering and balances the leaf surface and the number of flowers.
4. Cultisan Cu. Product that combines the multiple properties of chitosan with the antifungal power of copper. Recommended for the prevention of Phytophthora cinnamomi In post-flowering stages. Chitosan strengthens the roots and stimulates the tree's growth and defenses, creating a protective layer that prevents colonization by external agents.
5. Spiralis Long Life or your version ECO Long Life. Fruit of our R&D line of Natural Defensive BiotechnologyIt is an activator of systemic resistance, both acquired and induced. It promotes the accumulation of lignin and callose, strengthening cell walls, preventing or hindering their colonization by microorganisms, and also induces the synthesis of PR proteins and phytoalexins, providing the plant with defenses against a possible attack by pathogens.