INFLUENCE OF PACLOBUTRAZOL RESIDUES ON GREENHOUSE-BENCH SURFACES AND THE EFFECT ON GROWTH AND DEVELOPMENT OF CUCUMBER AND TOMATO YOUNG PLANTS

Application of Bonzi (paclobutrazol) as a foliage spray in pot plant c rops could lead to growth reduction in non-treated plants on the same table, but also in subsequent crops. Accurately cleaning and hosing th e greenhouse benches, using soft soap, or covering the bench surface w ith plastic sheets is not sufficient to avoid growth reduction. Cucumb er and tomato transplants grown on solid polystyrol greenhouse benches sprayed with 0.2 litre Bonzi-solution m-2 (20 ppm paclobutrazol per l itre water) and carefully cleaned, showed a reduction in height of 70 and 58%, respectively, when compared to the control. For tomato young plants these effects were almost equal with a foliage spray. Covering the bench surface with perforated or non-perforated plastic sheets, re duced to a certain extent the effect of the paclobutrazol residues. Yo ung plants of cucumber and tomato placed on the same bench as plants g iven Bonzi as a foliage spray also showed a reduction in height of 9 a nd 25%, respectively. For cucumber young plants, the sensitivity to pa clobutrazol residues decreased with increasing plant age, while the se nsitivity in tomato seemed to be the same during the hole propagation period.