Near the end of the June, I attended the summer PGR meeting and orchard tour that was held in Geneva, where Dr. Poliana Francescatto reviewed some of her recent work with PGR's. After a detailed discussion of floral bud induction and initiation indoors, we headed out to the research orchard to view a handful of her current field trials.  In this article, we will review some of the key takeaways from that tour.

Take away #1: Adjust Honeycrisp crop load early to maximize return bloom.

Poliana has found Honeycrisp initiates flowers earlier than other popular varieties. This initiation is the first visible sign that a bud is going to be a fruit bud, rather than a vegetative bud the following growing season. In Gala, initiation of the following season's flowers begins about 70 days following full bloom, with its peak around 85 days. In Honeycrisp, 95% of initiation is completed within 45-60 days after full bloom. Poliana explained how Honeycrisp's early initiation may play a considerable role in the cultivar's tendency for biennial bearing. While return bloom sprays have been used inconsistently to reduce biennial bearing in Honeycrisp, Poliana recommended regular and early thinning of Honeycrisp with NAA, followed by low weekly doses of NAA up to 40 days after full bloom to insure adequate return bloom the following season.

Take away #2: Using the Carbohydrate Model as One Tool in the Toolbox

The apple carbohydrate thinning model was developed by Dr. Alan Lakso and Dr. Terrence Robinson to model carbohydrate supply and demand using NEWA weather data and user entered field variables. Dr. Lakso was present at the meeting, and reminded growers that the model cannot always account for unique field circumstances, and that the grower ultimately knows their block history best.  A few growers shared how they like to use the model. One grower explained how he will apply a thinning treatment and then use the model to look back three days to better predict how effective the spray might have been. This helps him determine if he needs to go back in with another treatment when the next thinning window approaches.  The carbohydrate model can be used to determine daily carbohydrate stress during your thinning windows, but carbohydrate stress provides only part of the picture. Consider all of the additional chemical, physiological, and environmental variables that can impact your thinning each year when you develop your thinning program next May.

Take away #3: New Thinning Products

Poliana showed the group a few of her experiments with new thinning products. While not currently registered for thinning in the United States, Metamitron is a sugar beet herbicide that is already being used as a thinner in Europe.  She finds the greatest thinning effect from Metamitron occurs when fruit is between 8-12mm, and when there is a large carbohydrate deficit.  However, tree status prior to the application plays a significant role on the thinning responses. For instance, the carry-over effects of severe drought stress in 2016 explained a lot of the thinning responses seen in 2017. 

Two trees of Crimson Gala on M.9 treated with differing rates and spray timings of Metamitron, a sugar beet herbicide currently approved for fruit thinning in Europe.  

Poliana also discussed thinning with ACC, an ethylene precursor.  She finds ACC works best at the 18-20mm stage, but also works at the 8-12mm stage. The level of thinning from ACC is very dependent on temperatures at and following the application, and the thinning response is also heavily variety dependent.  Leaf drop can also occur using ACC, but it may be reduced if applied with or following an application of 6-BA.   

Take away #4: Strategies for Thinning without Carbaryl

Poliana is also investigating thinning programs that do not include carbaryl, as some retailers do not accept fruit treated with it. We visited a block of NY1 and NY2 where she showed very promising results using different combinations of 6-BA, NAA and NAD. So far, these combinations have had comparable thinning results to trees thinned with Carbaryl. We have seen similar thinning responses with these combinations in Honeycrisp at an on-farm trial in the Champlain Valley. In that trial, trees also received combinations of 6-BA, NAA, and NAD. Applications were made at bloom, petal fall, and 10-12mm. Poliana has developed carbaryl free thinning recommendations for major varieties, and discussed these recommendations at our petal fall meetings this past May.

For more information on Poliana's trials, review her recent article in the spring 2018 NYFQ.