In the most recent Fruit Quarterly (Vol. 28, No. 1, Spring 2020) Dr. Terence Robinson and co-authors introduce some improvements to the Cornell Apple Carbohydrate Thinning Model, also known as MaluSim. If you remember, MaluSim is a decision support tool to help make effective chemical thinning applications based on predicted thinning efficacy. Inputs to the model require temperature and sunlight which are derived from a NEWA weather station. Outputs include a daily Thinning Index and recommendation to increase or decrease chemical thinner rates. Many apple growers have indicated the MaluSim (Apple Carbohydrate Thinning) is one of the most widely used decision support tools on NEWA:
The rationale behind Robinson making these changes/improvements to MaluSim are based on their annual study from 2000 to 2011 where experimental thinning treatments (using carbaryl, NAA, and 6-BA) were applied to apple trees in Geneva, NY and annual data on flower bud density and then cropping (yield, fruit size) was recorded. Weather data was input into MaluSim where a daily carbohydrate balance during the chemical thinning period was calculated and compared to the crop load at harvest. It turns out:
- The greatest effect on fruit set was timing of chemical thinning application, with the best thinning occurring at 200 to 250 degree days (Base 39 degrees F.) Note that king fruit diameter centered about 12 mm during this window. (I remember my MSU colleauge Phil Schwallier, who has done many chemical thinning trials over the years, saying he has consistently got the best results when chemical thinners were applied when fruitlet size was 10 to 12 mm.)
- Initial flower counts (bloom intensity) have to be taken into the equation too. When there are more flowers, more aggressive thinning is needed vs. having fewer flowers.
- Carbohydrate balance also had an effect on fruit set, but was much reduced (or non-existent) outside of this degree-day window of 200-250 DD’s.
- And, the actual daily carbohydrate balance should be expanded to a longer period before and after the thinning application compared to the “old” MaluSim which used a 4 day running average to compute the daily carbohydrate balance.
So, based on this research the new Cornell Apple Carbohydrate Model on NEWA (Apple Carbohydrate Thinning v2019) was modified as follows:
- Users must input % flowering spurs before running the model, with four choices: 76-100%, 51-75%,, 26-50%, or 0-25%. (Note the user must also input green tip and bloom dates. Don't accept the NEWA default green tip date, enter your own. Bloom date should be when 80% of the flowers are open on the north side of trees.)
- Degree Days are automatically calculated, summed, and highlighted in the DD column when they are in the range of 200-250 DD’s (Base 39 degrees F.) from bloom.
- Calculation of the “Thinning Index” (daily carbohydrate balance) is expanded to seven days (two days before the day of thinning to four days after)
- And, thinning recommendation, taking into account % of spurs that are flowering, DD’s from bloom, and carbohydrate balance over seven days (all per above) will be color coded red=high risk of over-thinning, yellow=caution, possible over-thinning, green=expect good thinning, and blue=little or no thinning expected.
In 2019 the older Cornell Carbohydrate Thinning Model will be replaced by the new and improved Apple CHO Thinning v2019 MaluSim model and you are advised to use that. Note that CHO thinning is also available in the Malusim app available on both iOS and Android smartphones for mobile access to thinning recommendations.
 |
| Cornell Apple CHO v2019 NEWA interface |
 |
| Cornell Apple CHO v2019 NEWA output |
