Apple Carbohydrate Thinning Model-“Updates” for April 28 – May 1

The weather forecast predicts a hot and cloudy day for tomorrow (Saturday, April 29), which certainly will lead to more carbohydrate deficit. As you see from the graphs below, the carbohydrate balance will increase again by Tuesday and Wednesday, but the carbohydrate reserve will be below 20 g/day, which is not too high to influence thinning treatments (if needed) at this time.
For defruting you young apple trees (to fill the space and get a good tree structure), tomorrow might be a good day to do so. The temperature will be high (>85 oF) in Winchester and Central Virginia and the carbohydrate balance is very low (< -60 g/day) which together encourage for more fruit abscission. To defruit your trees, you can apply:
A) NAA (5-8 ppm) + Carbaryl (1-2 pt) + Superior oil (1qt)/100 gal; or
B) Ethephon (1-1.5 pt) + Carbaryl (1-2 pt) + Superior oil (1qt)/100 gal.
Although Ethephon should result in more aggressive thinning at such high temperatures; it might also cause tree growth reduction and might increase flowering the following year.
The following are the carbohydrate model outputs for both Winchester and Central Virginia.

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