Chemical and non-chemical thinning methods in apple (<i>Malus domestica</i> borkh)

Abstract

Thinning trials were conducted in the apple orchards of Klein Altendorf Experimental Station, Bonn, Germany using 7-year-old CV. ‘Cox orange’ and CV ‘Elstar’ apple trees in the year 2001 and 2002. The objectives were to find the effects of treatments on fruit set, yield, quality (i.e. fruit size) and to investigate how photosynthesis and transpiration are affected by one of the chemical thinners. The chemical thinning methods applied in the year 2001 were Ethrel (Flordimex) at 500ml/ha, Ethrel at 1000ml/ha, Ammonium Thiosulphate (ATS) sprayed to flowers on one year old shoots (ATS 1), Ammonium Thiosulphate (ATS) sprayed to flowers on older shoots (ATS 2), Amidthin plus Telmion, Amidthin plus Ethrel and unsprayed control. In 2002 the chemical thinning treatments applied were Azolon fluid (Urea formaldehyde), sprayed at 7.5li/ha and Ethrel (Flordimex) sprayed at 300ml/ha and unsprayed control. The non-chemical thinning method which was only applied in 2002 was partial defoliation of leaves. The experimental design used was randomized complete block design with three replications. The results showed that in the year 2001 Ethrel at 1000ml/ha had 67% thinning effect while Ethrel at 500ml/ha had 40% thinning. The other treatments had no thinning effect. Amidthin plus Ethrel had 22% yield reduction while Ethrel at 1000ml/ha had 30% yield reduction. ATS 2 had 44% increases in yield while ATS 1 had no effect. In terms of fruit size Ethrel 1000ml/ha had the best fruit quality (i.e. preferred diameter class of 70mm), followed by Amidthin plus Ethrel, Amidthin plus Telmion and Ethrel at 500ml/ha. In the year 2002 Azolon fluid resulted in 55% thinning in the first fruit set count before June drop while Ethrel had 56% and Azolon plus Ethrel 54% thinning effects which were not significantly different from defoliated treatment. Similar thinning trends were observed for fruit set counts after June drop. Transpiration and photosynthetic rates were reduced by 5% and 20%, respectively. Ethrel at 300ml/ha reduced yield significantly from 29.2kg/ha in the control to 25.5kg/tree while methylene urea (Azolon) had no effect. Thinning with methylene urea increased fruit size to 67% and Ethrel (Flordimex) to 79% of fruits larger than 70mm. It is concluded the chemical treatments thinned the fruits adequately and were not significantly (P ≤ 0.05) different from the non-chemical methods of thinning and fruit size was improved while transpiration and photosynthesis were slightly affected after Azolon application.