ABSTRACT
To determine the effect of fertilizers containing nitrogen, phosphorous and potassium on the population level of the citrus whitefly, nine combinations of fertilizer were tested on a 2 ha plot of Clementine trees. The fertilizer, in combinations of from zero to excess (quadruple) doses of each of the three elements N, P and K, was compared to a control plot receiving a normal dose. Each type of fertilizer was applied each year in a dose proportional to the age of the tree.
One sample per type of exposure, consisting of a leaf-bearing branch of the spring growth, was taken from 216 clementine trees at the centre of the individual subplots.
Variance analysis of the densities of citrus whitefly eggs has revealed sharp differences in the degree of infestation of the trees. The effect of the fertilizer is highly significant, and the plots showing an excess of all the nitrogen and phosphopotassium fertilizer differed from all the others in having very much higher egg densities. The analysis also established that only N2 and P2O5 were involved in the fertilizer effect, with increased doses of phosphorous and then of nitrogen giving rise to an increase in the embryo population of the citrus whitefly.
