Technical visit

Lemon orchard

Name: F.lli Corvaja

Location: South-east coast of Sicily, province of Siracusa.

Extension:135 Ha entirely level ground and at the sea level.

Main crops: One hundred hectares are used for dry or well-watered grass and vegetables crops while the remaining part is cultivated to lemon (cv “Limone di Siracusa”). This variety is very productive and has high quality fruit for oil composition as well as high citric acid, vitamin and juice (over 30%) content. Sweet orange (cv Navelina) is present only on a small area. Citrus replaced the original crops represented by vineyard and almond trees as well as cattle-breading. The orchard has plots with plants of different age and different distance between them (4.5´4.5/6.0´6.0m).

Soil: On average the soil can be classified as medium fine, basically clayey and with a sub-alkaline pH which is typical of the Siracusa province. The farm is provided with drain tubes to remove extra rain water.

Cultural practices: Every year the owners plan fertilization according to the results of a leaf analysis performed in October. Regularly they carry out end-winter and summer fertilization using mixed organic products added with chemical ones. Moreover, leaf fertilization is made in spring. Pruning is made every other year and the vegetable residues, after a careful inspection to exclude Phoma tracheiphyla infections, are reduced to little bits and buried during tillage. Weeds control is provided through 2-3 tillage operations per year.

Irrigation system: In the area there is a good amount of water available at a low depth (30m) so that the irrigation system uses only water from private underground wells. Irrigation is made with an under canopy aspersion system partly fixed and partly mobile.

Pest management: The farm adopts an Integrated Pest Management program and the necessary insecticide treatments are made mainly using mineral oil. Young trees are sprayed with Imidacloprid to protect summer flows (one or two) from Phyllocnistis citrella infestation.

Phyllocnistis citrella Stainton - In Sicily, due to the low efficiency of indigenous entomophagous detected on this pest, a classical biological control program has been started in 1995 by introducing, rearing and releasing the exotic Hymenoptera parasitoids Ageniaspis citricola Logvinovskaya (Encyrtidae), Quadrastichus sp. and Citrostichus phyllocnistoides (Narayanan) (Eulophidae). The first one was recovered in some coastal lemon orchards where it overwintered in 1998, although without any following permanent establishment. Quadrastichus sp. was found only after releases (1996), but it has not overwintered. C. phyllocnistoides overwintered in all the release sites and showed a high dispersal rate. At the moment it represents one of the main natural enemies of the citrus leafminer together with Semielacher petiolatus (Girault) (Hym. Eulophidae), recovered for the first time in 1998 and naturally spread in all citrus areas in Southern Italy.

Besides, one of the main pest on lemon is the Oleander scale (Aspidiotus nerii), which is rather hard to control mainly due to the lack of an effective monitoring system.

Aspidiotus nerii Bouché - This species is almost worldwide distributed on citrus and the number of generations per year varies between 3 and 8 depending on the temperature and humidity levels. It mainly overwinters as virgin female and immature male on various size branches. The reproduction is sexual or parthenogenetic and each female produces an average of 100 eggs with the parthenogenetic biotypes performing a lower fecundity. This scale insect is extremely polyphagous and it attacks citrus (mainly lemon), acacia, asparagus, carob, ivy, jojoba, kiwi, mulberry, oleander, olive, palm, peach, pear, plum. The pest attacks branches, leaves and fruits. Heavy attacks may cause loss of vigor, deformation of infested plant parts, chlorotic spots on leaves and leaf drop. On the fruits the feeding sites of the scales remain green and do not develop normally while the rest of the rind changes color at maturity and grows evenly. The oleander scale is attacked by the predatory beetles Chilocorus bipustulatus (L.), Exochomus quadripustulatus (L.) Rhyzobius lophantae (Blaisdell) and Scymnus spp. (Coleoptera Coccinellidae). The species is also parasitized by the Hymenoptera Aphytis chilensis How., A. chrysomphali (Mercet), A. diaspis (How.), A. hispanicus (Mercet), Encarsia citrina (Craw) (Aphelinidae) and Arrhenophagus albitibiae Girault (Encyrtidae). Regular pruning represents an important tool in controlling this scale as well as all the other scales. Chemical control can be performed using mineral oils before the scale moves on the fruits and, in case of heavier infestations, the use of an IGR (buprofezin) can be considered.

Finally, the control of Ceratitis capitata infestations is a problem for the farm on Navelina orange, mainly due to the very few authorized insecticides on citrus against this pest in Italy.

Diseases:

Rumple (Wrinkle rind - Corteza arrugata) - A disorder primarily of lemons which first appears in late summer, when fruits turn yellow, at first as chlorotic sunken areas of the rind, with yellow discolorations between the glands, restricted to flavedo tissue. Glands progressively become greenish brown, tan, and finally brownish black. Ultimately they flatten and collapse. After fruits break colour, some areas remain brown whereas others turn to greenish black. The disorder is related to physiological unbalance mostly affecting water translocation to the fruits, therefore a different percentage of affected fruits may be observed, with the climatic conditions, rootstocks, varieties and clones, each fertilization and irrigation.
Psorosis (Citrus psorosis virus - Ophiovirus) - Trees infected by the psorosis virus may gum profusely in the later stages of the disease. In the early or later stages before bark scaling is evident, psorosis is detectable by small flecks, from light green to yellow in colour, lying along the small vein lets of young leaves. Psorosis brings about scaling bark lesions on sweet orange (mostly the navel group), grapefruit and mandarins, and stunting of some trees. This disease usually appears first on the older bark of the trunk or limbs; it is evidenced by small scales with or without gum formation. As the disease advances the wood layers become infiltrated with gum and hard, resin like materials, and later become stained a reddish brown.
Concave gum disease - It is found on orange and mandarin trees. On trunk and limbs it produces relatively broad concavities – a result of the virus’ retarding and at times arresting the formation and growth of wood in the affected parts. Bark covering these depressions is apparently normal, but may sometimes crack open and allow gum ooze to the surface. Tissue on the surface layers of wood is gummy or granulated and reddish brown in colour. Young leaves seasonally show the oak leaf pattern of clearings.
Impietratura - The disease has the name “impietratura” because the fruit turns hard like a stone. Fruit drop, reduction in size, various patterns of skin hardening, and albedo gumming are the characteristic symptoms in citron, grapefruit and oranges trees. No specific symptoms are reported for leaves.
Mineral deficiencies - Iron as well as manganese and magnesium deficiencies, are quite diffused as a result of the calcareous lime soil.
“Mal secco” disease (Phoma tracheiphila) - Phoma tracheiphila (Petri) Kanc. & Ghik is the causal agent of citrus mal secco disease. The principal host species is lemon, although the disease also has been reported on many other Citrus spp. as: citron, bergamot, lime, sour orange and rough lemon. Mal secco is present in the citrus-producing countries in the Mediterranean and Black Sea areas. The fungus penetrates the plant through wounds and reaches the vascular system, causing different symptoms, including leaf vein chlorosis, yellowing and leaf drop, twig and branch dieback, and eventually, the death of the tree. Removal of the bark of shoots and branches can reveal typical pink-salmon or red discoloration of the xylem.

	TECHNICAL EXCURSION
	Lemon orchard Name: F.lli Corvaja Location: South-east coast of Sicily, province of Siracusa. Extension:135 Ha entirely level ground and at the sea level. Main crops: One hundred hectares are used for dry or well-watered grass and vegetables crops while the remaining part is cultivated to lemon (cv “Limone di Siracusa”). This variety is very productive and has high quality fruit for oil composition as well as high citric acid, vitamin and juice (over 30%) content. Sweet orange (cv Navelina) is present only on a small area. Citrus replaced the original crops represented by vineyard and almond trees as well as cattle-breading. The orchard has plots with plants of different age and different distance between them (4.5´4.5/6.0´6.0m). Soil: On average the soil can be classified as medium fine, basically clayey and with a sub-alkaline pH which is typical of the Siracusa province. The farm is provided with drain tubes to remove extra rain water. Cultural practices: Every year the owners plan fertilization according to the results of a leaf analysis performed in October. Regularly they carry out end-winter and summer fertilization using mixed organic products added with chemical ones. Moreover, leaf fertilization is made in spring. Pruning is made every other year and the vegetable residues, after a careful inspection to exclude Phoma tracheiphyla infections, are reduced to little bits and buried during tillage. Weeds control is provided through 2-3 tillage operations per year. Irrigation system: In the area there is a good amount of water available at a low depth (30m) so that the irrigation system uses only water from private underground wells. Irrigation is made with an under canopy aspersion system partly fixed and partly mobile. Pest management: The farm adopts an Integrated Pest Management program and the necessary insecticide treatments are made mainly using mineral oil. Young trees are sprayed with Imidacloprid to protect summer flows (one or two) from *Phyllocnistis citrella* infestation. *Phyllocnistis citrella* Stainton - In Sicily, due to the low efficiency of indigenous entomophagous detected on this pest, a classical biological control program has been started in 1995 by introducing, rearing and releasing the exotic Hymenoptera parasitoids Ageniaspis citricola Logvinovskaya (Encyrtidae), Quadrastichus sp. and Citrostichus phyllocnistoides (Narayanan) (Eulophidae). The first one was recovered in some coastal lemon orchards where it overwintered in 1998, although without any following permanent establishment. Quadrastichus sp. was found only after releases (1996), but it has not overwintered. C. phyllocnistoides overwintered in all the release sites and showed a high dispersal rate. At the moment it represents one of the main natural enemies of the citrus leafminer together with Semielacher petiolatus (Girault) (Hym. Eulophidae), recovered for the first time in 1998 and naturally spread in all citrus areas in Southern Italy. Besides, one of the main pest on lemon is the Oleander scale (*Aspidiotus nerii), which is rather hard to control mainly due to the lack of an effective monitoring system. Aspidiotus nerii* Bouché - This species is almost worldwide distributed on citrus and the number of generations per year varies between 3 and 8 depending on the temperature and humidity levels. It mainly overwinters as virgin female and immature male on various size branches. The reproduction is sexual or parthenogenetic and each female produces an average of 100 eggs with the parthenogenetic biotypes performing a lower fecundity. This scale insect is extremely polyphagous and it attacks citrus (mainly lemon), acacia, asparagus, carob, ivy, jojoba, kiwi, mulberry, oleander, olive, palm, peach, pear, plum. The pest attacks branches, leaves and fruits. Heavy attacks may cause loss of vigor, deformation of infested plant parts, chlorotic spots on leaves and leaf drop. On the fruits the feeding sites of the scales remain green and do not develop normally while the rest of the rind changes color at maturity and grows evenly. The oleander scale is attacked by the predatory beetles Chilocorus bipustulatus (L.), Exochomus quadripustulatus (L.) Rhyzobius lophantae (Blaisdell) and Scymnus spp. (Coleoptera Coccinellidae). The species is also parasitized by the Hymenoptera Aphytis chilensis How., A. chrysomphali (Mercet), A. diaspis (How.), A. hispanicus (Mercet), Encarsia citrina (Craw) (Aphelinidae) and Arrhenophagus albitibiae Girault (Encyrtidae). Regular pruning represents an important tool in controlling this scale as well as all the other scales. Chemical control can be performed using mineral oils before the scale moves on the fruits and, in case of heavier infestations, the use of an IGR (buprofezin) can be considered. Finally, the control of Ceratitis capitata infestations is a problem for the farm on Navelina orange, mainly due to the very few authorized insecticides on citrus against this pest in Italy. Diseases: Rumple (Wrinkle rind - Corteza arrugata) - A disorder primarily of lemons which first appears in late summer, when fruits turn yellow, at first as chlorotic sunken areas of the rind, with yellow discolorations between the glands, restricted to flavedo tissue. Glands progressively become greenish brown, tan, and finally brownish black. Ultimately they flatten and collapse. After fruits break colour, some areas remain brown whereas others turn to greenish black. The disorder is related to physiological unbalance mostly affecting water translocation to the fruits, therefore a different percentage of affected fruits may be observed, with the climatic conditions, rootstocks, varieties and clones, each fertilization and irrigation. *Psorosis (Citrus psorosis virus* - Ophiovirus) - Trees infected by the psorosis virus may gum profusely in the later stages of the disease. In the early or later stages before bark scaling is evident, psorosis is detectable by small flecks, from light green to yellow in colour, lying along the small vein lets of young leaves. Psorosis brings about scaling bark lesions on sweet orange (mostly the navel group), grapefruit and mandarins, and stunting of some trees. This disease usually appears first on the older bark of the trunk or limbs; it is evidenced by small scales with or without gum formation. As the disease advances the wood layers become infiltrated with gum and hard, resin like materials, and later become stained a reddish brown. Concave gum disease - It is found on orange and mandarin trees. On trunk and limbs it produces relatively broad concavities – a result of the virus’ retarding and at times arresting the formation and growth of wood in the affected parts. Bark covering these depressions is apparently normal, but may sometimes crack open and allow gum ooze to the surface. Tissue on the surface layers of wood is gummy or granulated and reddish brown in colour. Young leaves seasonally show the oak leaf pattern of clearings. Impietratura - The disease has the name “impietratura” because the fruit turns hard like a stone. Fruit drop, reduction in size, various patterns of skin hardening, and albedo gumming are the characteristic symptoms in citron, grapefruit and oranges trees. No specific symptoms are reported for leaves. Mineral deficiencies - Iron as well as manganese and magnesium deficiencies, are quite diffused as a result of the calcareous lime soil. “Mal secco” disease (Phoma tracheiphila) -** Phoma tracheiphila (Petri) Kanc. & Ghik is the causal agent of citrus mal secco disease. The principal host species is lemon, although the disease also has been reported on many other Citrus spp. as: citron, bergamot, lime, sour orange and rough lemon. Mal secco is present in the citrus-producing countries in the Mediterranean and Black Sea areas. The fungus penetrates the plant through wounds and reaches the vascular system, causing different symptoms, including leaf vein chlorosis, yellowing and leaf drop, twig and branch dieback, and eventually, the death of the tree. Removal of the bark of shoots and branches can reveal typical pink-salmon or red discoloration of the xylem.