Due the rapidly changing weather forecasts, I ran the MaluSim model again on Thursday. For Central Virginia, the model is showing values in the -20 to 20 range for the next seven days. This means that growers should expect an “average” response from their chemical thinners. Growers in the Central Virginia region should target the next couple-few days to make their thinning sprays as fruitlets are at the ideal size for applications of NAA and 6-BA. Fruitlets grow at ~0.5 mm/day in cool temperatures, and as you can see from the table below, up to 1 mm/day with warmer temperatures.
Table 1. Fruitlet sizes at Silver Creek Orchards.
Much warmer day and night temperatures are forecast for the Winchester area, so the MaluSim model is showing a persistent carbohydrate deficit for the next five days. However, we are still at petal fall to ~5 mm for most cultivars, so hopefully by the time fruit are at 10 mm more moderate weather conditions will reduce the chance of over thinning. Chemical thinning applications made when either the day-by-day or running average value is below -60 g CHO/day will likely result in aggressive thinning.
I will run the models again early next week. Please download the below pdf files for the full report.