Essais d’éclaircissage chimique des pommiers (Malus domestica L. Borkh) « Gala » et « Red Top Spur » dans la région de Meknès au Maroc

Chemical thinning of apple (Malus domestica L. Borkh) cultivars « Gala » and « Red Top Spur » in Meknès area of Morocco. Several factors can contribute to excessive fruit set in apple which usually leads to small fruit of poor quality and could increase the risk of biennial bearing. In this study we tested the effectiveness of the naphthalene acetic acid (NAA) at 1.0 and 1.5 g.100 l-1 and the N-methyl carbamate of naphthyl-1 (carbaryl) at 80 and 100 g.100 l-1 in thinning two apple cultivars « Gala » and « Red Top Spur ». The control treatments consisted of manually thinned and non thinned trees. The chemicals were applied when the king fruits reached the stage of 10 to 12 mm or 17 days after full bloom. The results varied with the cultivar, the chemical and its concentration. This variation appeared at the evolution of fruit drop, the proportion of clusters bearing less than 4 fruits, yield and fruit size. The carbaryl at 100 g.100 l-1 gave excellent results for both cultivars consisting of proportions of fruit drops, clusters with few fruits, fruits of higher size and fruit yield similar to those of the hand thinned control trees. In contrast, NAA, in addition of its insufficient thinning effect, induced the formation of « pygmy fruits » on « Red Top Spur » which led to a reduction of fruit yield and fruit size.