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NEWA Carbohydrate Model Run for May 7, 2021

This is the MaluSim Carbohydrate run from the morning of May 7, 2021, for all of the grower-reported sites in Pennsylvania.

Updated:

May 7, 2021

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On May 6, 2021, we had an online Spring Orchard meeting. Besides the updates in the disease, insect, and FSMA information, Jim Schupp gave his estimation of the chemical thinning prospects so far this season.

Jim mentioned in his presentation that temperatures at FREC are not predicted to move out of the 60s for the immediate future. To be the most efficacious, many of the PGR chemical thinners need temperatures to be at least in the 70s. None of the sites participating from across the state will be in that range. Nor is the longer-range prediction for the state to warm up.

Ideally, the warmer the temperature, the more thinning response you will notice from an application of thinners. Of course, as mentioned yesterday, if high temperatures soar into the upper 70s to 80s; application could lead to over thinning. We did show some high temperatures at some sites in the upper 70s to lower 80s around April 25–27 but that was around full bloom. It would be interesting to know if any growers tried an application of Amid Thin-W in that period.

The other factor most growers look for is fruit size being in the 10 to 14 mm diameter size. The 2021 Carbohydrate (CHO) model uses a growing degree day prediction of this stage to occur sometime between 200–250 GDD base 39°C. Only the sites in Adams County are approaching or in the lower end of this range.

The third factor you need to look at is the “Fifth Column” of the tables. This is the daily CHO balance. A negative value means the trees are under a deficit of CHO production and will be more responsive to thinner applications. In the tables today (links below) all daily balance values are positive. Positive values mean trees will be less responsive to a thinner application.

Finally, if you look at the predicted 7-Day Average Balance (the Sixth Column) those are also positive. Therefore, predictive effects on the trees for the immediate future do not look good for optimum thinning weather.

Jim summarized his presentation about the possibility of needing to use the “rescue treatment” of ethephon later at larger fruit diameter. All three of the Spring Orchard meetings were recorded so watch your email for the recording links.

I want to thank the participating growers for their support of this project and their diligence in reporting their flowering stage.

The MaluSim Carbohydrate Model