STRAWBERRY Fragaria x ananassa YIELD RESPONSES TO SEVERAL DENSITIES OF Tetranychus urticae (Acari:Tetranychidae) UNDER GREENHOUSE CONDITIONS

Abstract

Strawberry plants of cultivar Selva were infested with Tetranychus urticae Koch and mites were permited to reach densities up to: A, 5; B, 25; C, 50; D, 75 mites per leaflet, in order to compare yield with respect to infested and mite-free (clean) controls, and in such a way to determine the maximal density that can be supported by the plants without causing a reduction in yield and fruit quality. Densities of T. urticae were standarized in accumulated mite-days per leaflet (CMD/L). CMD/L observed were: clean control, 0.64; A, 227.10; B, 1324.94; C, 2494.94; D, 3791.58; infested control, 12742.09. Significant differences with respect to clean control were observed in the number of fruits bigger than 2.54 cm in diameter, in its weight and total weight of the fruits, except with the density of 5 mites/leaflet. No significant differences were found in the total number, total and individual weight of fruits smaller than 2.54 cm in diameter, in treatments with low mite densities. The variables of fruits of highest quality were the most reduced as an effect of mite feeding. A close negative correlation was found between log of CMD/L and evaluated variables. It was determined that with a density between 127 and 341 CMD/L it is not necessary to control the mite in the cultivar tested.