DEVELOPMENT OF A RAPID SCREENING METHOD FOR PRELIMINARY ASSESSMENT OF BLOSSOM DESICCANTS AND ADJUVANTS

Field assessment for determining the potential of chemicals as thinning agents is laborious and time consuming, and can result in significant damage to trial trees. With the increased use of desiccating chemicals and a range of adjuvants for crop thinning of perennial fruit trees, a method for rapid screening of blossom desiccants and/or potential adjuvants would enable smaller, more efficient field trials using only those treatments that have shown potential in screening tests. The objective of this work was to determine whether different adjuvants influenced the desiccating effect of the blossom thinner potassium thiosulphate (KTS). Flowering spurs of ‘Gala’ apple were collected from the orchard and treated in the laboratory. Two rates of KTS were applied without surfactant or with the following: Tween 20, Silwet L-77, winter (petroleum) oil, canola oil, fish oil, or Codacide (emulsifiable vegetable oil blend). Following treatment application, spurs were monitored to assess drying time, and the number of damaged stigmas and styles recorded up to 48 hours after treatment to determine the degree of desiccation. Drying time was reduced by all surfactants, with Silwet L-77 having the greatest effect. Winter oil reduced the desiccating effect of KTS. Fish oil had the greatest desiccating effect on both stigmas and styles, with 100% of stigmas desiccated 24 hours after treatment. Both Tween 20, the standard surfactant used with thinning chemicals, and fish oil resulted in higher levels of desiccation than KTS without surfactant when applied with the half rate of KTS. This laboratory assessment method has potential as a valuable rapid screening tool, however further studies correlating laboratory and field results are needed.