Agronomic means for the control of iron deficiency chlorosis in deciduous fruit trees

Iron deficiency induced chlorosis represents the main nutritional disorder in fruit tree orchards grown on calcareous and/or alkaline soils. Until roo tstocks tolerant to Fe deficiency chlorosis are available for most suscepti ble fruit species, the agronomic means of preventing or curing Fe deficienc y chlorosis will be considered of utmost importance by fruit growers. Chlor osis of fruit trees has been successfully controlled through foliar or soil applications of Fe chelates, which are expensive and have to be applied an nually. In this paper results of research carried out within an EU joint re search project are reported, where the effectiveness of alternative, low-in put, environmentally friendly management techniques to control Fe deficienc y chlorosis has been tested in established kiwifruit, peach and pear orchar ds located in the Po Valley (Italy), in the Ebro Valley (Spain) and in the area of Imathia (Greece). Iron sulphate supply to the soil proved to be eff ective only if applied together with high amounts of organic matter such as compost or manure, Promising results in preventing chlorosis were obtained by sowing a mixture of graminaceous species along the tree row and supplyi ng them with Fe sulphate. Laboratory tests indicated that long lasting decr eases of pH in calcareous soils are difficult to achieve. We have also foll owed two approaches using foliar sprays: 1) testing a variety of compounds which may activate the Fe pool likely present in chlorotic leaves (citric, sulphuric, ascorbic and indole-3-acetic acid) and 2) applying Fe sources al ternative to synthetic Fe chelates. Sprays aiming to activate the Fe pools in a chlorotic leaf were generally effective, although rarely caused a full recovery. This suggests that inactivation of Fe occurs outside the mesophy ll cells. Sprays of Fe sulphate in all the crops tested showed similar or e ven higher regreening effect than FeDTPA.