News

NEWA Carbohydrate Model Run for May 21, 2021

We have had unusually warm temperatures for most of this week and all stations report good to very good efficacy for any thinners that may have been applied.

Updated:

May 21, 2021

Skip to the end of the images gallery

Skip to the beginning of the images gallery

I hope that all growers have taken advantage of this week to apply chemical thinners to their apples and pears. Locations in the south and eastern portion of Pennsylvania are seeing a rapid closure of thinning windows. The model that we have been running is based upon Gala green tip and full bloom. If you have later blooming cultivars there still may be good responses to the application of thinners based upon the size of the fruit.

We are looking for a maximum response when fruit size hovers around 10 to 15 mm. Based on the GDD model, most of Adams County areas and southeastern Pennsylvania are entering or will soon achieve 350 GDD. Western Pennsylvania and the northern regions still seem to have lower GDD values indicating that fruit size could still be within the target diameter size.

If you failed to remove enough fruit from previous applications, then your last resort may be a combination of carbaryl and ethephon. Rates for ethephon would be 0.5–1.0 pt./100 gallons or 2–4 pt./A. Ethephon has been shown to remove apples up to 24 to 27 mm in diameter. As the temperature goes into the mid-80s or higher it can take off more fruit than desired. Therefore, use the lower rates especially on Golden Delicious and Rome, and other easy-to-thin cultivars.

Table 1–17 on page 75 of the current Tree Fruit Production Guide lists some of the cultivars based upon how they respond to chemical thinners. There is also the possibility of adding a pint to a quart of spray oil per 100 gallons. Be aware that the combination of Captan and oil can cause leaf phytotoxicity symptoms. If you need to use oil in a thinning spray keep Captan out of the spray and the next two cover sprays. As always keep good records of the responses to your thinners and weather.

After you have finished all of your thinner applications, I would urge you to go back to the Carbohydrate model on the NEWA website and choose a weather station close to your location enter your green tip and full bloom of your cultivars and run the model for the entire season. You can highlight and copy the Model table and past it into an Excel document. Annotate the Excel table when and what you applied to serve as a record for comparison of the success of your chemical thinner applications.

The MaluSim Carbohydrate Model

Network for Environment and Weather Applications (NEWA)