As we see harvest coming right around the corner, the time to apply ReTain for drop control is upon us. Dr. Duane Greene from UMASS presented at the 2015 UVM Apple Program / Vermont Tree Fruit Growers Association meeting on the use of ReTain and NAA for drop control, slides from his talk can be found at: http://www.uvm.edu/~fruit/treefruit/tf_meetings/PGRsVTFGA15.pdf
- The ReTain label limits application to a maximum of 333g active ingredient per acre, but lower rates and multiple applications may be made.
- Earlier application timing results in greater delay in ripening, later timings improve drop control.
- Multiple applications at reduced rates may be more successful than a single application.
- NAA (Fruitone) may also improve drop control but when used alone may advance ripening and reduce storage life.
- NAA when applied with a half-rate or ReTain will improve drop control with less delay in ripening and reduction in red color than ReTain applied alone.
Growers should consider beginning ReTain applications on September-ripening cultivars (McIntosh, Gala, Cortland, Honeycrisp) in the next week if they have not already. Full rates may be made at this time, or half rates so long as a follow up spray will be applied. Inclusion of 10 ppm NAA may be warranted on cultivars and blocks where poor color development has been an issue where ReTain was used alone. A second application of ReTain may be made in another two weeks. This will allow for harvest of McIntosh and Gala beginning the week of September 7. For Honeycrisp and Gala, lower rates may be warranted. All ReTain sprays should include a non-ionic surfactant to increase uptake of the active ingredient. Plant growth regulator applications should be made alone without tank-mix components that may reduce material effectiveness.