Abstract: [Objective] Effects of spraying plant growth inhibitors on the leaf diseases, early defoliation and reflorescence of pear trees were studied for improvements on prevention and control of the commonly occurred defects on pear trees in areas under hot and humid conditions. [Method] Five-year-old Cuiguan pear trees were sprayed with one of the 5 plant growth inhibitors or water (control) to observe the effects on the growth of shoots and leaves as well as the occurrence of leaf diseases, early defoliation and reflorescence. [Result] The chemicals applied controlled the growth of shoots in varying degrees ranking in the order of paclobutrazol > PBO > flusilazole > propiconazole > monopotassium phosphate. These inhibitors stopped shoot elongation 27.8 d, 15.2 d, 19.4 d, 18.8 d and 11.5 d, respectively, sooner than did control. On the leaves, paclobutrazol stimulated their growth, while the other chemicals exerted varying degrees of inhibitory effect on the growth. All inhibitors either significantly or extremely significantly alleviated the leaf diseases or delayed the early defoliation and reflorescence. The indices on 4 major diseases in various periods after treatments ranked in the order of flusilazole < PBO < propiconazole < monopotassium phosphate < paclobutrazol. The control effect of the inhibitors on early defoliation were in the order of flusilazole > PBO > propiconazole > monopotassium phosphate > paclobutrazol. The defoliation was delayed 25 d by flusilazole, 22 d by PBO, 20 d by propiconazole, 15 d by monopotassium phosphate, and 12 d by paclobutrazol. [Conclusion] Chemical control could be effective for leaf and flower retentions of a pear tree. Spraying combined agents might produce better effect.

Key words: pear, plant growth inhibitor, control of shoot growth, leaf retention, flower retention