Thinning of 'Golden Delicious' apples with new thinning compounds

Six year old apple trees 'Golden Delicious'/M9 were sprayed with new thinning compounds and their combination. Application of ammonium thiosulphate (ATS) 0.5 % did not thin while ATS 1% doubled the yield of bigger fruits. 1- naphthaleneacetic acid (NAA) 10 ppm affected a strong but still reasonable thinning – the mean fruit weight was increased. Spraying of 6-benzyaldenine (BA) 50 ppm had no influence on fruitlet abscission while BA 100 ppm thinned the best – shifting the fruit to bigger size class was so strong that no yield per tree was lost. Ethephon 150 ppm applied alone had no thinning response. Consecutive spraying of ATS 0.5 % and BA 50 ppm did not reduce the yield significantly but the mean fruit weight was enhanced. All the combination sprayings of NAA 10 ppm with ATS 0.5 %, ethephon 150 ppm or BA 50 ppm respectively, caused a too strong thinning response so that the yield of bigger fruit was diminished too. Return bloom was increased with all chemical thinning treatments except when single agents BA 50 ppm, BA 100 ppm or ethephon 150 ppm were applied.