Cornell Cooperative Extension Hudson Valley Regional Fruit Program
Michael J. Fargione, Extension Educator

Tree Fruit Recorded Message for Friday, May 20, 2011

Let’s just say that this is a difficult year to figure out how to approach thinning. We are seeing cropload all over the board, with good bloom and fruit set for some blocks and varieties, and poor return bloom and/or winter injury to fruit buds in other sites (such injury can be determined by looking for short fruit stems or even missing king fruit or whole clusters). In addition, I have been running the Lakso-Robinson carbohydrate model, and the results are now available on our website for Hudson, NY ( ) and Marlboro, NY ( ). This model indicates trees throughout our area have been running carbohydrate deficits due to the extended cloudy weather we have experienced since green tip. These deficits have been alarmingly large at times, and beyond my past experience. Some blocks are already showing small fruitlets shucking off. What is a grower to do?

Here is our best advice on thinning at this time:
1. Steve Hoying made this statement early and we think it holds very true. This is the year to wait as long as possible before thinning to gain as much knowledge of how fruit will respond to past (and upcoming) carbohydrate deficits. You can still obtain adequate thinning results out to 15mm king fruit size. Most blocks can wait until next week before they are thinned, and that is our recommendation. In the meantime, scout, scout, scout.

2. If fruit size is at the effective limit (king fruit at 14-15 mm) or you cannot cover all the ground in time, then carefully evaluate the current set and start your thinning. Yesterday, Dr. Terence Robinson indicated that the model shows the carbohydrate deficit this week was not as severe as expected from the weather forecast (to me, the deficit looked greater in Hudson than in Marlboro). Beginning now, the predicted thinning index (an average of the carbohydrate deficit for a given day plus the next 3 days) is about –20g. Dr. Robinson suggests this is a mild to moderate deficit which should help give good thinning. He also believes the more serious deficit of the past week should not make trees respond excessively to thinners applied in coming days. If you thin over the coming weekend, he suggested going with normal rates where set looks strong, but drop the rates by at least 30% where there was a lighter bloom or poor set.

3. Consider adding carbaryl to “petal fall” sprays this weekend on hard to thin cultivars (Jonamac, Gala, Macoun, Honeycrisp, Empire??) where set is heavy and you plan to wait until next week to do your “normal” thinning.

4. Remember our pest management and thinning meetings are scheduled for this Monday. Details are at: .

5. Finally, I would caution growers that rumors have it that this year’s crop may bring good prices, as the 2010 crop is moving out quickly and weather-related problems in other areas may limit the size of the 2011 national crop. If you can’t make up your mind what rates to use, my suggestion is to be conservative and err on the side of less-aggressive thinning, particularly on high-value cultivars where you can afford to do some hand-thinning.