The effectiveness of AVG used in a single and combined application with NAA against preharvest fruit drop in apple

Abstract

The results of four experiments carried out in years 2007, 2008 and 2010 in the Research Institute of Horticulture in Skierniewice on the apple cultivars ‘Gala Must’ and ‘Ligol’ are presented. The preparations ReTain® (as formulation VBC-30033) containing AVG (aminoethoxyvinylglycine) and Pomonit Super 050SL (as salt of NAA with triethanoloamine) were used against preharvest fruit drop by spraying the trees alone and subsequently. Retain® was used 4 weeks before anticipated harvest at two doses: 180 and 360 mg L-1, and Pomonit Super one week before harvest at 20 or 40 mg L-1. The effect on the dynamics of fruit drop, on fruit quality at harvest and after storage, as well as on shoot growth and subsequent flowering was determined. In all experiments it was found that the lowest number of apples abscised before the harvest when both preparations were used at half of optimal doses, respectively, at four and one week earlier. The efficiency of subsequent use of preparations was better than the use of ReTain® alone at twice higher dose (optimal). The effect on preharvest fruit drop of low dose of ReTain® used alone was too weak. No significant effect of preharvest treatments with ReTain® and Pomonit Super on the total yield of apples, and on the average fruit weight was found. However, in 2008 in both cultivars the combined treatment with low doses of ReTain® and Pomonit Super, caused distinct increase in percentage of large apples (>70 mm diameter), while other treatments with preparations have no effect on the distribution of apple in the individual classes of fruit size and on average fruit weight. The effect of both preparations on other parameters of apple quality depended on the cultivar. Treatment with ReTain® alone at high and at low dose, but combined with NAA, caused a significant reduction of red color of apples in ‘Gala Must’, but significant increase in flesh firmness at harvest and after storage. However, on the cultivar ‘Ligol’ no effect on red color of apples and reduction of firmness was found. In 2010 it was also shown that before the harvest, abscission could be avoided by twice application of Retain® 40 days before anticipated harvest and Pomonit Super 10 days before anticipated harvest, both in doses reduced by half as compared to what was previously recommended.