Manage of crop load to improve fruit quality in plums

Abstract

The crop load of European plums must be adjusted to achieve high quality with adequate size and skin color in order to attend market requirements. The present study had the objective to investigate the effects of chemical and mechanical thinning, applied isolated and in combination of both, at different phenological stages of Katinka plum growing in Southern Germany. The following thinners were tested: mechanical thinning, chemical thinning with Ammoniumthiosulfate - ATS, Ethephon, Prohexadione-Calcium and Gibberellin. Mechanical thinning treatment isolated or associated with ATS. Significantly increased fruit drop and reduced the yield. It also, increased fruit size and fruit weight when compared to the control plants. Also Ethephon increased fruit drop and fruit size when compared to the control plants. Among to other chemical treatments, no positive effects were observed for fruit thinning when compared to the control plants.

Efficacy of Chemical Agents in Reducing Fruit Set of ‘Leticia’ Japanese Plums

“…Ethephon had no effect on fruit set in this experiment. This result is corroborated by Pavanello et al (2018) where ethephon did not promote flower thinning and had little effect on fruit set. This growth regulator has variable results and the weather conditions have a huge influence on the performance, as when sprayed later in the season, it tends to be more effective than when used at early spring, due to the colder temperatures in the beginning of the season (WEBSTER; SPENSER, 2000).…”

“…Similarly, for 'Golden Delicious' apples, Myra et al (2007) found that sodium chloride indeed reduced pollen grain germination on an in vitro experiment, but in field conditions it had a mild performance in reducing fruit set, although the caustic compounds lime sulphur and ammonium thiosulfate were effective in reducing pollen grain germination, pollen tube development and on reducing fruit set. In contrast, for European plums, Pavanello et al (2018) found no effect of ammonium thiosulfate on reducing fruit set. Although, for peaches, El-Boray et al (2013) reported that ammonium thiosulfate at 3% v/v and soybean oil at 9% v/v reduced fruit set, and increased leaf area, indicating that somehow these treatments also stimulate vegetative growth, and maybe it causes restriction of assimilates for the flowers.…”

“…Stone fruit manual thinning may be quite expensive WILLEMSEN, 2002;MEITEI et al, 2013;PAVANELLO et al, 2018), especially because most producers are smallholder farmers with limited availability of resources. Although, pome fruits have the inconvenient of having a non-uniform flowering, with flowers at different phenological stages at blooming (FALLAHI, WILLENSEN, 2002).…”

Ammonia thiosulfate in Japanese plum tree thinning

“…This is the first report dealing with ATS use on Japanese plum in Brazil. Previous studies carried out with European plums under the influence of 3% ATS concentrations during full blooming did not culminate to thinning satisfactory results (Pavanello et al, 2018). Recent research taking into consideration ethephon on physiological responsiveness of fruit plants have had a consistent impact on thinning (PAVANELLO & AYUB, 2012, however such a product did not evidence permission of application in plum orchards at commercial scales.…”

“…Fruits with a diameter greater than 44 mm are accepted for commercialization AYUB, 2012;AHRENS et al, 2014). The increase in the plum diameter was proportional to the increase of ATS concentrations, due to the reduction of the excess fruit produced in the accesses, as observed under the mechanical (HEHNEN et al, 2012) and chemical thinning (PAVANELLO, AYUB, 2012, PAVANELLO;ZOTH;AYUB, 2018). The composition of the ATS has a fertilizing effect, mainly having nutrients such as sulfur and nitrogen (FERNANDES, 2010), which when applied to flowering causes an increase in apple diameter of 10 to 12 mm (MAAS, 2007).…”