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NEWA Carbohydrate Model Run for May 17, 2021

You should be hearing the sprayers running across the state this week. The weather has finally warmed up.

Updated:

May 17, 2021

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Photo: Rob Crassweller

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Highs are expected to be in the upper 70s to low 80s. Carbohydrate daily and 7-day average balances are negative for all sites in this report. The majority of the sites show that the risk of overthinning is low except for some sites in the west of the state, Rock Spring, and North East Escarpment. Some specific sites are still recommending an increase in chemical thinner rates. I believe the primary reason for this is based on GDD values; suggesting that fruit size is larger than desired.

One problem that I have observed in our orchard is the differential timing and potential size difference of the fruitlets. We have some fruit that were 8 to 9 mm in diameter this weekend. We also still have some late bloom that has yet to set. Since the majority of our fruit are approaching the minimum 10 mm size we intend to apply thinners this week probably on Wednesday. We will have to deal with the late bloom later and hope that the warm temperatures will still push the straggling fruit for an application next week after our current 8–9 mm fruit are beyond reach.

Fruit size differential. Photo: Rob Crassweller, Penn State

As in the previous reports released, the first column is the date of the run. The second and third columns are the expected high and low temperatures. The fourth column is expected solar radiation. Solar radiation, as you know, is what drives photosynthesis, the process of producing carbohydrates for fruit and tree growth. The fifth and sixth column is the daily and expected 7-day carbohydrate balance from the MaluSim model. The more negative the values indicate a deficit and potential for greater response to a chemical thinner application. The seventh column is a calculated growing degree day value. This is used to help estimate fruit size.

Based on research fruit is estimated to be most responsive to thinner application when the GDD is in the 200 to 250 GDD range; or approximately 10 to 14 mm diameter. The last column is the suggested general dosage rate of what your standard thinning chemical should be. Those general rates can be found in Table 1–15A (page 67) and 1–15B (page 69) in the 2021–22 Penn State Tree Fruit Production Guide.

This is also a good time to remind you about the color coding added to the tables this year. There are three sets of color codes. The first column lists the date with green shading indicating the date the model was run and the blue shading previous dates and tan shading future dates. In the next seven columns, the text color indicates the efficacy of a thinner that is applied on those specific dates. Good efficacy and very good are indicated by the green and orange text, respectively. Red text indicates the possibility of an excessive response for a thinner application. The last column shaded color codes indicate the possibility of overthinning with green shading being a low risk of overthinning and red shading a danger of overthinning.

The MaluSim Carbohydrate Model

Network for Environment and Weather Applications (NEWA)

Finally, if you want to see how this year's conditions compare to last year you can go back and look at previous years’ model outputs. To do so enter the dates from last year’s green tip and bloom date and select the date you applied your chemical thinner.