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 rootstocks tolerant to Fe deficiency chlorosis are available for most susceptible fruit species, the agronomic means of preventing or curing Fe deficiency chlorosis will be considered of utmost importance by fruit growers. Chlorosis of fruit trees has been successfully controlled through foliar or soil applications of Fe chelates, which are expensive and have to be applied annually. In this paper results of research carried out within an EU joint research project are reported, where the effectiveness of alternative, low-input, environmentally friendly management techniques to control Fe deficiency chlorosis has been tested in established kiwifruit, peach and pear orchards 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 effective 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 supplying them with Fe sulphate. Laboratory tests indicated that long lasting decreases of pH in calcareous soils are difficult to achieve. We have also followed 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 alternative 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 mesophyll cells. Sprays of Fe sulphate in all the crops tested showed similar or even higher regreening effect than FeDTPA.