Metamitron and Different Plant Growth Regulators Combinations in the Chemical Thinning of ‘Eva’ Apple Trees

Aims: The objective of this study was to evaluate the effect of the application of Metamitron and the combinations of NAA + BA and Promalin + BA on the fruit thinning of the Eva cultivar apple tree in southern Brazil.

Study Design: The experimental design used was a randomized complete block design, with four replications, with two plants per treatment in each block, following a one-step scheme with 10 treatments for the thinning factor.

Place and Duration of Study: The experiment was carried out in the agricultural year of 2013/2014 in a commercial orchard located in the municipality of Morro Redondo, RS, Brazil (Lat. 31º 40’ 60” S and Long. 52º 34” 50” W).

Methodology: Spraying of Metamitron was carried out at doses of 300, 350 and 400 mg L-1 and combinations of 5 mg L-1 of NAA + BA at doses 50, 75 and 100 mg L-1 and 0.5 ml L-1 of Promalin® + BA at doses of 50, 75 and 100 mg L-1. Only the doses of Promalin® were applied in full bloom, the other sprayings were carried out in fruiting with 5-8 mm in diameter. The variables analyzed were: number of fruits per trunk section area, number of fruits per plant, yield per plant, mean fruit mass, pulp firmness, fruit shape and diameter, fruit length, length/diameter ratio and soluble solids.

Results: A reduction in harvest load by Metamitron was only observed with the 300 mg L-1 dose. The combination of NAA 5 mg L-1 + BA 75 mg L-1 showed the highest fruit reduction, with a low fruit density per cm-2 and the highest average fruit mass. For the combinations of Promalin® + BA, as the increment of the dose of BA increased, there was a reduction of the number of fruits and consequently an increase in their size.

Conclusion: It was concluded that the Metamitron at the dose of 300 mg L-1 was able to cause thinning when applied in the fruit formation phase (5-8 mm). And the combinations of NAA 5 mg L-1 + BA 75 mg L-1and Promalin® 0.5 ml L-1 + BA 100 mg L-1 were able to reduce harvest load and increase the fruit size.