Citrus problems: the expert answers on citrus diseases


THE AGRONOMIST ANSWERS ON HOW TO GROW AND CARE FOR PLANTS

PROBLEMS ABOUT CITRUS FRUITS

Citrus spp. (family

Rutaceae

)

The column is dedicated to citrus fruit issues. If you wish to write to our agronomist in order to have an answer on a problem concerning your plant, it is necessary that you indicate:

The section is dedicated to plant problems.If you wish to write to our agronomist in order to have an answer on an unclear situation or a difficulty concerning your plant, it is necessary that you indicate:

  1. what plant it is;
  2. where it is located (inside the house, on the terrace, in the garden, etc.);
  3. the type of exposure (full sun, half-light, etc.);
  4. how long has it been in your possession;
  5. the general state of the plant;
  6. the frequency of watering;
  7. how often it is fertilized and the type of fertilizer used;
  8. any pesticide treatments carried out;
  9. the symptoms it presents and the parts of the plant affect;
  10. any foreign presence (insects or other).

If possible, send a photo, but in any case, take care to be very detailed in describing the overall state of the plant. The address to which everything is forwarded is: [email protected]

Your questions


It is called "Black spot of citrus fruits" and risks destroying Sicilian oranges, lemons, mandarins and clementines / MORNING 467

This terrible fungal disease is not yet present in Europe. But in the last year the seizures of sick citrus fruits that could spread this pathology among the citrus fruit plants of our island have multiplied, where the Tristeza virus has already created enormous problems for the Red Oranges of the Catania Plain. CIA and Confagricoltura: immediately block imports of citrus fruits from Tunisia. Problems also with citrus fruits from South America

Is there a maneuver in place to destroy Sicilian citrus cultivation and, in general, Southern Italy? The question is more than legitimate if we go and examine what is happening. The problems come from Tunisia, the country that, since 2016, has been flooding Europe - Italy in the lead - with olive oil at bargain prices, creating enormous problems for real Italian extra virgin olive oil. Problem we have addressed in this article. Now we are recording strange maneuvers on citrus fruits. With the possible arrival from various parts of the world - for example, South America and North Africa - of pathogens absent in Europe until now.

Let's read what ITALFRUIT NEWS writes:

"The European citrus production chain is very worried about the continuous interception of loads from the Southern Hemisphere infested with harmful organisms and / or diseases not yet present in Europe, starting from Citrus Black Spot (CBS). In fact, in June 2020 alone, Europe encountered an abnormal quantity of contaminated lemons from Argentina. 32 interceptions of CBS were recorded and two more of the causative agent of bacterial cancer of citrus fruits, Xanthomonas citri ".

In particular, the Citrus Black Spot (CBS), a fungus that causes a disease called “Black spot of citrus”. Responsible for this pathology is the Guignardia citricarpa, an Ascomycete fungus that affects citrus plants in all subtropical climates, causing a weakening of the tree which is accompanied by a reduction in production with negative effects on the quality of the fruit.

This year the cases of interception on citrus fruits from the Southern Hemisphere rise to more than 60.

"The latest episode - we always read on ITALFRUIT NEWS - occurred just a few days ago at the port of Naples, where the Phytosanitary Service of the Campania Region found a load of South African oranges with Phyllosticta citricarpa, quarantine pest that causes CBS. Numbers and data that are scary. This is why, on the sidelines of its last meeting, the citrus fruit contact group between Italy, Spain, Portugal and France drew up a common position on the phytosanitary risks associated with products imported from third countries ”.

Problems with imported citrus fruits were recorded this year in Catania, as you can read here and as you can also read here.

Also on ITALFRUIT NEWS we read a statement by Elena Eloisa Albertini, member of the Fruit and Vegetable Coordination of the Alliance of Agri-food Cooperatives (ACI):

"The entire European citrus production chain believes that it is essential to make cold treatment mandatory on all non-EU citrus loads entering Europe. Only in this way is it possible to limit the risk that a devastating disease such as CBS can enter our continent. This was one of the requests that the Citrus Contact Group brought to the attention of the Commissioner for Health, Stella Kyriakides, and to the Agriculture Commissioner, Janusz Wojciechowski. In fact, it makes no sense that we Europeans, when we export citrus fruits around the world, have to carry out cold treatment, while this obligation does not apply to the overseas fruits we import ".

Let's go back to our question: what is happening - the many loads of blocked citrus fruits, citrus fruits arriving in Europe from other parts of the world, carriers of pathogens hitherto absent in our parts - is a coincidental fact, linked to the madness of globalization of economy, or is there a direction behind it to destroy European citrus productions, to open the doors to imports?

Let's read what AgriNotizie writes:

“The European Commission's phytosanitary inspections have recently detected the presence of the fungus Guignardia citricarpa, which causes the citrus disease known as Cbs (Citrus Black Spot) out of seven shipments imported from Tunisia. The news of the presence of CBS on the shores of the Mediterranean is alarming. After South Africa, Argentina, Uruguay and last but not least Brazil, where the number of wiretaps increased exponentially in 2018, the danger can no longer be ignored ”.

Citrus fruits imported from Tunisia enter the scene.

AgriNotizie reports a note from the CIA, the Italian Confederation of Farmers, where we read that, if the CBS "spread, it would cause irreparable damage to the citrus heritage, putting at risk one of the most important sectors of our agriculture in the South".

“At a time when the sector is trying to overcome the problem of Sadness - which has already caused enormous damage - and is engaged in the search for new outlet markets, we absolutely cannot expose ourselves to the attack of a new plant disease ".

Tristeza is a viral disease that affects orange trees. In Sicily it caused enormous damage to Sicilian Red Oranges: a topic we addressed three years ago. And that we recently picked up.

In light of the problems that CBS could create for Sicilian citrus fruits, the CIA calls for "the protection of imports of citrus fruits from Tunisia, with increased controls by the Commission".

The president of the National Citrus Federation of Confagricoltura, Gerardo Diana, asks for more drastic remedies:

“The news of the presence of Citrus Black Spot in Tunisia - we always read on AgriNotizie - is absolutely alarming. After South Africa, Argentina, Uruguay and Brazil, now the danger can be said to be on the doorstep, as it was recently detected in seven expeditions from Tunisia to the European Union. We have always drawn the attention of the competent authorities to this plant disease which is currently not present in Europe but which, if it spreads, would cause irreparable damage to the citrus fruit heritage, putting one of the most important sectors of our southern agriculture at risk ".

Confagricoltura therefore proposed the immediate blocking of imports from Tunisia, the increase in controls and the Commission's commitment to a rapid review of Community legislation which will have to be more rigorous, revising international agreements.

AgriNotizie takes stock of the situation in Sicily "where 57% of national citrus fruit production is concentrated, with over 10 million quintals of oranges, 4 million lemons, 600,000 tangerines and 500,000 quintals of clementines per year".

He says Giuseppe Di Silvestro, president of CIA Eastern Sicily:

"We propose an immediate blocking of imports from Tunisia, an increase in controls and a commitment by the Commission to a rapid revision of Community legislation".

Di Silvestro launches an appeal to the president of the Sicilian Region:

"We ask President Nello Musumeci to make his voice heard on the national tables to deal with the emergency".

Photo taken from Cinque Colonne Magazine


A quarantine insect

A. spiniferus initially it can be mistaken for a cochineal due to its small size and the dark color of the juvenile forms which are immobile and vaguely resembling the Parlatoria spp. The adults, on the other hand, are winged and mobile, blackish in color and covered by a veil of whitish waxy dust. The wings have rounded white spots near the edges on a dark background.

Like other whiteflies, A. spiniferus produces abundant honeydew on which fumaggine easily develops and can attack various cultivated plant species (guests of choice are citrus fruits, but persimmon, pome fruit, vine, rose, etc. are also infested) or spontaneous (eg. 'ivy).

Due to its polyphagia, the insect is potentially harmful not only to citrus fruits but also to other agricultural and ornamental crops. For this A. spiniferus is included by Eppo (European and Mediterranean Plant Protection Organization) in the list (A2) of the organisms whose adoption of quarantine measures is recommended and in the list of plant diseases for which the introduction and spread in the European Union (EU Annex II / A1).

Preimaginal stages of A. spiniferus. Due to their shape and color they can be mistakenly confused with a cochineal


Pedoclimatic needs

Being plants of tropical origin, they have particular needs towards the climate to obtain, in fact, a valid commercial production it is necessary that this is warm, sufficiently humid, with mild winters and without wide temperature ranges, even if a moderate presence of the latter allows in Mediterranean areas the appearance of anthocyanin and carotenoid pigments, responsible for the color in oranges and mandarins, which is impossible, due to their absence, in the tropical areas of origin. They generally carry out their vegetative activity at temperatures between 13 and 30 ° C. Relative to the cold, they are damaged by temperatures below 0 ° C with varying intensity depending on the species and variety. Temperatures above 38 ° C are also harmful, especially if they occur in coincidence with conditions of low relative humidity and during the fruit set phase.
The presence of strong and persistent winds can cause serious damage to citrus crops (drying of leaves and young shoots, mechanical breakage of branches, wounds from rubbing on the fruits themselves). To overcome these problems, windbreaks (dead or alive) are often used.
In our climates, to obtain a valid production, the annual rainfall should be well distributed and exceed 1,800 mm. Therefore, in Italy, irrigation is almost always necessary.
Regarding the soil, citrus fruits prefer loose or medium-textured, deep, fertile, well-drained (they cannot withstand water stagnation), with a pH between 6.5 and 7.5 and well endowed with organic substance. They shun soils that are too clayey, calcareous and salty.


Ferlazzo N. Anti-Inflammatory Activity of Citrus bergamia Derivatives: Where Do We Stand? Molecules 2016 21 (10): 1273

AAVV. Culture & Culture. Citrus fruits

Michela Trevisan. Health! Ed. Pentagòra, 2015

Dr. Michela Trevisan

nutrition biologist, Kousmine method consultant, NUPA and ISDE member, author of the books: weaning according to nature, free from allergies and intolerances, if you do not eat vegetables, the manual of fermented foods, eat healthy and spend little, long and healthy life, Health! Foods for the care of the person, the home, the garden

Dr. Roberta Franceschini

nutrition biologist, Kousmine method consultant, NUPA member


Diseases of the lemon tree

We have already talked about this plant when we talked about how to prune lemon. The diseases of the lemon tree that we are going to describe they are of various types. They can be viral, therefore due to a virus, bacterial, due to a bacterium, or fungal, due to a fungus.

No one is more serious than another, because any disease becomes serious only if neglected. When you notice its appearance, it is necessary to intervene as soon as possible with suitable plant protection products (whether they are of natural or chemical derivation) and with the help of an expert.

Tristeza virus

The Tristeza, scientifically said Citrus Tristeza Virus, is the most serious disease of lemons. It manifests itself in a particularly vigorous way towards grafted plants. It is also called Sadness of citrus fruits, given the particular symptoms that derive from it.

THE symptoms of Tristeza virus they are not specific and can also be confused with other diseases that are easier to treat. The evolution of symptoms can be summarized in the following list.

  • Yellowing of the whole plant
  • Fall of the leaves
  • Conspicuous enlargement of the stem, in the part above the graft
  • Desiccation of the plant
  • Browning of the internal tissues (phloem) of the graft area
  • Death of the plant

In the graft site, the virus alters the "suck" of nutrients and water by the plant. This causes the symptoms described above. Obviously also at a radical level. Attention must also be paid to the spread of the virus. The disease, in fact, is infected both through the infected plant material and by various aphids (Aphis citricola is Myzus persicae).

How the tristeza virus is treated

The cure against Tristeza virus it is purely preventive. It basically consists in the implementation of some agronomic interventions that aim to limit the contagion and spread of the virus. These interventions are:

  1. Choice of coupling combinations (subject-scion) resistant to disease
  2. Eliminate the aphids Tristeza virus vectors
  3. Total destruction of plants infected by fire, so as to eliminate all sources of contagion

Collar rot (or lemon chewy)

Gummy is a disease caused by a fungus: Phytophthora citrophthora. (R.E. Sm. & E.H. Sm., Leonian, 1906). This is also particularly vigorous in the case of plants grafted on non-resistant rootstocks. It typically occurs in the collar area, with the emission of rubber from the cortex. The evolution of symptoms can be described as follows:

  • The underground part rots and is surrounded by intense humidity
  • The peel of the plant browns, necrots and cracks
  • The underlying wood is impregnated with rubber
  • The roots rot and crack
  • The infection progresses to extend to a large part of the plant
  • The foliage withers and the leaves turn yellow
  • The branches dry out
  • The fruits are affected in the case of high rainfall
  • When the infection takes the whole circumference of the plant, it dies

How to cure collar rot

The fight against rot is agronomic and chemical. There agronomic struggle sees the use of rootstocks resistant to rot (bitter orange or others), the burglary at the right depths, the improvement of drainage, the elimination of irrigation by sprinkling, the avoidance of too clayey soils and the grassing of the inter-row . While the agronomic struggle is preventive, the chemical fight, must be carried out at the first symptoms. First of all, it is necessary to eliminate the infected cortex and treat the wound with products based on neutral copper salts or with systemic products such as Propamocarb, aluminum Fosetil and Metalaxyl-M. These products can also be distributed to the ground, by spraying.

Piticchia of lemon

The lemon pit is caused by a bacterium: Pseudomonas syringae (Van Hall, 1904). This is also one of the most common lemon plant diseases. It occurs especially at the end of winter, on the still young and green twigs and on the fruits. The symptoms can be summarized as follows:

  • The branches, in the points of attachment of the leaves, have necrotic, brown and depressed notches
  • The notches are also present on the leaf petioles
  • A drop of rubber comes out of the notches
  • In severe cases, the infection extends to the entire circumference of the branch
  • The leaves wither and dry out
  • On the lemons there are dark brown notches called "piticchie"
  • The size of the notches varies from 10 to 20 mm in diameter
  • In severe cases, a bacterial exudate also comes out
  • The fruit is still edible but loses quality

How to take care of the lemon piticchia

Among all the diseases of the lemon tree, piticchia is perhaps the simplest but at the same time most burdensome to eradicate. There agronomic struggle, preventive, consists of fertilizing the citrus grove in a balanced way, avoiding excess nitrogen, destroying infected vegetation by fire and protecting citrus groves from the wind (with windbreak barriers). There chemical fight, on the other hand, it is carried out only in the event of a serious attack. It consists of performing monthly treatments from October to March, using copper-based products (Bordeaux mixture, hydroxy and oxychlorides).


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Citrus fruits, few remedies for alternating flowering

In citrus fruits, the alternation of production is a common phenomenon in many varieties, with repercussions on the yield and quality of the fruit. The phenomenon is partially controlled by the presence of fruits that can drastically reduce it, with a consequence of a smaller number of fruits (year of discharge or off), followed by a year with a flowering and abundant production (year of charge or on) . To the lower production must be added the damage to the quality of the low-caliber fruits in the year of loading and large pieces with rough skin in the year of unloading, with problems of a commercial nature for the placement of the product. In this context, it is necessary to try to establish a balance, thanks to a cultivation technique, which allows for adequate quantitative and qualitative production. To reduce the alternation of production it is necessary to decrease the vegetative flow in the year of discharge, to reduce the reserves that could feed an excess of flowering the following year. On the other hand, in one year of charge, the vegetation must be stimulated to achieve the formation of reserves in the branches and leaves, to achieve good flowering the following year.

Irrigation and fertilization

In the charging year, the irrigation and fertilization level must be increased to allow for a vegetative development that can feed a good flowering the following year. In the year with poor harvesting, irrigation and fertilization must be reduced to low levels, to reduce vegetative excess. The potassium content in the leaves drops a lot when this is used for fruit growth. An intake of water and potassium and nitrogen fertilizers in the summer during the charging year will decrease the energy expenditure of the plant with a smaller reduction in production in the following year.

Reduce or increase flowering

The reduction of production can be achieved in two different ways: - with thinning and pruning to reduce the number of fruits - with techniques for the reduction of flowering. The flowering of citrus fruits is a complex phenomenon that is influenced by endogenous and exogenous factors, among the first a fundamental role is played by gibberellins, which have an inverse relationship with flowering, greater presence of gibberellins, less presence of flowers and therefore fruits. The fruits synthesize gibberellins, for which an abundant harvest, or a permanence of the fruits on the tree, cause an increase with the subsequent reduction of the flowering in the following spring and, therefore, of the harvest. Therefore, early harvesting reduces the inhibition of flowering. Among the exogenous factors, low temperatures and water stress induce flower formation. The low winter temperatures reducing the radical activity therefore reduce the synthesis of gibberellins and the transport to the canopy, allowing the induction of spring flowering. In this sense it is evident that the vegetative rest phase is the period of greatest sensitivity to flower induction processes. Studies also suggest that floral induction of low temperatures is accompanied by a reduction in the level of endogenous gibberellins, which therefore play a very important role in inducing flowering. Water stress also plays an important role, being enough for 40 to 60 days of stress to promote flowering. From the above it can be said that the induction of flowering occurs during the winter rest period. Therefore, this phase is the most appropriate to manage the final destination of the gem, increasing or decreasing, as appropriate, the percentage of buds per flower. Applications in this period of gibberellic acid (GA3) reduce the percentage of flowers, while applications of foliar urea or potassium phosphite increase it.

Foliar applications to reduce flowering

To reduce flowering there are two phases of greater sensitivity to gibberellic acid. The first phase is during the winter rest between the end of November and mid-December, in this phase the application of 20-30 ppm of gibberellic acid reduces the spring flowering, and consequently the production. The second phase in which you can intervene when the buds begin to move up to a maximum length of 3 mm. However, this period is much shorter than the previous one and since the phenological state is not the same, it is more difficult to determine the correct time to perform the treatment. In this case the doses to be used are 10 ppm. However, winter interventions with gibberellic acid reduce flowering, however this reduction does not always lead to a lower production. On many occasions, a redistribution of spring vegetation occurs, with the increase of shoots with leaves (vegetative, mixed and bell-shaped shoots) and with the reduction of leafless shoots (flowering branches and solitary flowers). The mixed buds and campanulaceae favor fruit development as the leaves are a source of energy for the phenological phases of fruit set and development. This leads to an increase in spontaneous fruit set, as the number of harvested fruits is not reduced. In this case, the treatment with gibberellic acid does not reduce production, but it improves the size of the fruit and increases the incidence of commercial sizes. For the late varieties when the fruits are present on the plant, the use of gibberellins can cause a delay in the coloring of the fruits, to overcome this problem you can reduce the dose to 10 ppm or do not carry out any intervention, trying to regulate the flowering. with the pruning and thinning of the fruit.

Interventions to increase production

To increase the production of a year of discharge, you can use the incision or the application during the winter rest of foliar urea with a low content of biuret or potassium phosphite. Foliar application of 0.5% urea or 0.15% potassium phosphite (0-28-26) during the winter in the floral induction and initiation phase, determines an increase in the number of fruits and consequently , of production, especially in the years in which low production is expected (discharge year). Numerous studies on winter applications of foliar urea or potassium phosphite demonstrate the effect of inducing greater flowering and production, although the time of application and other factors such as variety, geographic location, nutritional status of the plant, etc. they can determine a different response of the tree to these treatments.

Combination of treatments to increase and reduce production

During the winter rest period, it is possible to use in a combined manner, in alternate years, gibberellic acid (20-30 ppm), before the flowering of one year of filler and foliar urea (0.5% N) or potassium phosphite ( 0-28-26) to 0.15%, before flowering in one year of discharge. In tests conducted on 'Valencia Late' in an extremely alternating field, the treatments carried out had not achieved the desired effectiveness, but it was possible to increase production with the increase in commercial caliber. The combination of treatments was as follows: 24 ppm GA3, applied in pre-flowering in one year of scarcity and foliar urea, free of biuret, 0.45% or potassium phosphite (0-28-26) 0.15 %, pre-flowering of one year of discharge. Treatments with foliar urea or potassium phosphite carried out in previous years of poor harvest increased both total production and commercial size. Furthermore, in the years of high harvest, the application of GA3 did not lead to a reduction in production, but it favored a redistribution of flowering, increasing the percentage of flower buds with leaves (mixed flowers and campanulacea), greater fruit set and fruit size. .


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