Asian Journal of Plant Sciences1682-39741812-5697Asian Network for Scientific Information10.3923/ajps.2007.1155.1157Malus domestica)]]>George Ouma 7200767Experiments were carried out at Klein Altendorf station in 2001 and 2002 with the objectives of finding the effect of the chemicals and defoliation on yield, fruit set and quality of apples and investigate how photosynthesis and transpiration are affected by one of the chemical thinners (i.e., Azolon). At a dose of 10 mg ai/Li Ethrel (Flodimex) thinned better than at 5 mg ai/Li in 2001 while at 3 mg/Li in 2002 it achieved the required fruit set by thinning before June drop 62 and 15%, respectively after June drop compared to 49% of the unsprayed control and improved fruit size while yield per tree was reduced by 31% by Ethrel at 10 mg ai/Li but not Ethrel at 5 mg i/Li which had no effect on yield. Mean fruit weight was unaffected by the treatments. The foliar urea based fertilizer Azolon fluid at 75 mg ai/Li applied at full bloom, resulted in 61% fruit set before and 17% after June drop in 2002, slight leaf yellowing, killing and epinasty 7 days after treatment application which disappeared 14 days later but probably started earlier and a slight reduction in leaf photosynthesis and transpiration rates. However, Azolon fluid (i.e., methylene urea or urea formaldehyde) yielded smaller fruit than Ethrel (Flordimex), but larger fruits than the untreated control trees, without affecting fruit yield. The partial and gradual defoliation of selected primary spur leaves reduced fruit set to 50% before and 14% after June drop. These results provide evidence that reductions in photosynthetic rate or photosynthetic leaf area during the period of flowering is sufficient and can successfully induce thinning with a commensurate efficacy of the chemical thinners.]]>Byers, R.E., J.A. Barden and D.H. Carbaugh,1990115913Byers, R.E., D.H. Carbaugh, C.N. Presley and T.K. Wolf,199166717Dennis, F.G.Jr.,200031116Groschowska, M.J. and A. Lubinska,197329425429Knight, J.N.,198055267273Lakso, A.N. and L.C. Grapadelli,1992322231239Proctor, J.T.A. and J.W. Palmer,199166275282Quinlan, J.D. and A.P. Preston,196843373381Quinlan, J.D. and A.P. Preston,197146525553Stopar, M.,199773461466Untiedt, R. and M.M. Blanke,20013519Weaver, R.J. and R.M. Pool,1971Vitis viniferas L.).]]>10201209