Action of some micronutrients on the infestation and yield components of faba bean by the aphid, Aphis craccivora Koch (Aphididae, Homoptera) and the leaf miner, Liriomyza trifolii (Burgess) (Agromyzidae, Diptera)

Field experiments were carried out in the two growing seasons of 1999/2000 and 2000/2001 on faba bean (Vicia faba) plants in the Experimental Farm of Agriculture Research Station at Nubaria region, Alexandria, which is considered as a newly reclaimed calcareous soil. The present investigation aimed to evaluate the effect of spraying faba bean plants with certain micronutrients, i.e. Iron, Manganese and Zinc either in single double or triple combinations on the infestation by the aphid, Aphis craccivora Koch (Aphididae, Homoptera) and the leaf miner, Liriomyza trfolü (Burgess) (Agromyzidae, Diptera). The infestation by these insects was assessed using the parameters of Infestation grades as well as the injury indices. Faba bean plants cv. Giza Blanca were sprayed twice (45 and 66 days) after planting with the above-mentioned micronutrients. However, results of this investigation showed, with no doubt, that Mn, Zn and Fe individually or in double or triple combinations have increased to varied extents the infestation rates (%) of faba bean plants compared to the untreated ones. Such varied increases were mainly due to the metabolic roles of the used foliar sprays and their interactions, which indirectly affect the physio-biological actions of plants that may render them suitable for either A. craccivora or L. trifoii reproduction. This phenomenon might be also due to the different environmental factors. In both seasons, the relationship between nutrients applications and pests Infestation followed the same trend of increase in the percentages of infested plants. This assures and confirms the constant metabolic roles of such micronutrients. The biological seed weight (ton/fed.) was positively affected by the application of the used micronutrients. It is worth mentioning that the maximum response was observed in case of the triple treatment followed by the double and single treatments in a descending order. Application of the investigated micronutrients alone or in mixtures resulted in significant increases in yield and its components. Such increases were due to the fact that ions of Zn, Fe and Mn are cofactors of several enzymes, but rarely if ever with a high degree of specificity.