TECHNICAL EXCURSION
  
 

Orange orchard

Name: Grimaldi

Location: Lentini territory (Siracusa province), locality Xirumi.

Extension:200 Ha in a level ground area suitable for citrus cultivation at an average altitude of 80m a.m.s.l.

Main crops: Several citrus species and varieties are grown (orange, clementine, tangerine) but orange is the main one. The main rootstock is Citrus aurantii but Citrange Troyer is also used (about 10%). The most important orange cultivars grown, in extent order, are: Tarocco, Valencia late, Navelina, Moro and Ovale. Particularly, the Tarocco clone “Scirè” is the most cultivated (50 – 60%) for its good competitiveness on the fresh fruit market due to various characteristics such as early pigmentation (between the end of October and mid November) and persistence on the tree. The average plant age varies from 10 to 25 years and the trees are planted at a distance of 6´4 m.

Soil: The soil is autochthonous and has a medium composition with a good content of organic substance, increased by recurrent manure fertilization and buried cultivation residues.

Cultural practices: Pruning is made regularly by turns. Weeds control is provided by tillage while a fertilization plan is drawn up every year following leaf and soil analysis using organic and mineral compounds. Leaf fertilization is performed only on nucellar Tarocco.

Irrigation system: Irrigation is made with an under canopy fixed aspersion system and the water is provided by private underground wells.

Pest management: The farm adopts an Integrated Pest Management program according to the agro-environmental regulation of the rural development plan of the Sicilian Region. Several Citrus pests are present in the orchard but their population density is well maintained under damage economic threshold by natural enemies. The chemical treatments are made, almost exclusively, with mineral oil, in case activated with Chlorpyriphos – methyl to control occasional high infestations of Aonidiella aurantii.

  • Aonidiella aurantii (Maskell) is a key pest of Citrus groves in Italy. It was firstly detected at the begin of XX century and till 1930 it was confined in restricted areas of Liguria, Campania, Lazio and Puglia districts infesting almost exclusively lemon. From the 70s the scale has been spreading out in the main citrus areas of Southern Italy and during the Eighties diffused in almost all the citrus groves damaging all species and varieties of Citrus. Since its first appearance, a classical biological control programme has been carried out by introducing the aphelinid wasp Aphytis melinus DeBach that was rapidly established in all cultivation areas. Among the several natural enemies detected in Italy, A. melinus (Hymenoptera Aphelinidae) and Chilocorus bipustulatus (L.) (Coleoptera Coccinellidae) are the most effective and the former shows to be the most important biotic mortality factor. The scale performs 3-4 generations per year and especially if mild winters occur it may reach the intervention threshold. California red scale control is generally based on IPM strategies supported by a monitoring system realized with pheromone traps. The male captures data related to Degree Days calculation allow to determine the appropriate period to proceed with chemical treatments (mainly with mineral oils) or biological applications (augmentative releases of A. melinus). During the visit, we plan to see an experimental plot where Aphytis melinus augmentative releases have been carried out for several years to control California red scale and a plot of trees grafted on Citrange Troyer where the same pest is chemically treated when necessary.

 

Diseases:

  • Citrus Greasy spot (Micosphaerella citri) - Greasy spot is caused by the fungus Mycosphaerella citri. This disease can cause serious premature defoliation during the fall and winter on sweet orange, lemon, grapefruit and mandarin type, resulting in reduced yields and fruit size. The disease is induced by high relative humidity or spring rains. Leaf symptoms first appear as a yellow mottle on the under surface of the leaves. Growth of hypha inside the leaf tissue causes cellular swelling resulting in blister formation on the lower leaf surface and produces yellow to brown spots. Later, the swollen tissue starts to collapse and turn brown and eventually the brown or black symptoms become clearly visible on the upper side of the diseased leaves as well. Infected leaves often drop before the lesions develop a dark greasy appearance. Greasy spot infection on fruit produces pinpoint black specks which occur between the oil glands.

Wind machines: Citrus is subject to damage from freezing weather in temperate climates, as in the Mediterranean area.The damage could range from injuries to blossom and young fruit, to reduced production, to heavy tree damage and even loss of large orchards. Wind machines are technical equipment designed specifically for microclimate environmental modification. The fans mix the layers of warm and cold air, raising the temperature at the surface. Incorporating the spray in the same machine (Polyguard) used for frost protection allows easily the applications of chemicals for pest management. The drops are carried in the air flow generated by the fan.