I have received several reports of green-tip across the state and wanted to remind growers that if you will be running the carbohydrate thinning model in NEWA, you need to record the date of green-tip stage for all cultivars. The model will start calculating carbohydrate production at green-tip, so it is critical to record the date in order to have an accurate prediction of the trees’ carbohydrate balance.

This year two new parameters have been added to the model based on long-term thinning studies by Terence Robinson and his research team at Cornell University. Percent Spurs Flowering, refers to % of spurs that are flowering in one of 4 ranges (0-25, 26-50, 51-75 and 76-100%). This information will adjust the recommendation on the severity of thinning, so that if trees have a light bloom, the severity of thinning will be less, while a heavy bloom will recommend a greater thinning severity. Adding the Percent Spurs Flowering parameter to the model helps to offset the long-term study result that trees with more blossoms will always end up with more fruit. To calculate the Percent Spurs Flowering, select two branches of a representative tree in the block and count the number of total spurs and the number of flowering spurs at tight to open cluster.

The second parameter added to the model is Growing Degree Day calculation with a base temperature of 4°C (39°F). The results from the long-term thinning study from Cornell show the effect of carbon balance was greatest at 200-250 DD after bloom and was much less at earlier or later timings. Meaning that fruits are most sensitive to chemical thinning in this 200-250 DD window, which corresponds to when fruitlets are about 12 mm in diameter.

Some of the changes you will see in the model output include:

• The calculation of the Thinning Index (running average carbohydrate balance) now incorporates the average carbohydrate balance for 2 days before applying thinners and the next 4 days, for a total of 7 day running average.
• The column of the thinning recommendations will be based on a new 3-dimensional lookup table considering Growing Degree Day accumulation from bloom, % of spurs that are flowering and carbohydrate balance over 7 days.
• The thinning recommendation cells in the table will also be color coded to indicate red=high risk of overthinning, yellow= caution possible aggressive thinning efficacy, green=good thin­ning efficacy and blue= little or no thinning expected.

This article was posted in Apples and tagged Amaya Atucha, Apples, carbohydrate thinning model, Malusim.