Pennsylvania Ag Connection - Keystone Apple Carbohydrate Thinning Model Run

Pennsylvania Ag News Headlines

Keystone Apple Carbohydrate Thinning Model Run
Pennsylvania Ag Connection - 05/26/2020

Into the early part of this week, the weather appears to favor a good response to the application of chemical thinners, reports Robert Crassweller, Ph.D., a professor of horiculture for Pennsylvania State University.

Maybe in some cases, too good of a response at the Butler County site.

"I believe the combination of predicted warm temperatures and the lower sunlight levels have resulted in lower photosynthetic rates and therefore, lower carbohydrate production," noted Crassweller.

Thinner application is predicated on the average fruit size on the trees. As mentioned in a virtual twilight meeting on May 14, fruitlets are most responsive to thinners at 10 to 12 mm in diameter.

"We also mentioned the cold events that occurred across the state necessitate the need to examine flower survival," he said.

Overall, the fruit at Rock Springs are not near size for a thinner application. There are still some cultivars that have open flowers while early cultivars like McIntosh are still under the 10 mm size. Nine sites across the state have recommendations to decrease the standard rate of thinner. Of course, the "standard rate" will vary based upon your experiences, and the cultivar that you are going to thin.

Typically, at Rock Springs, Don starts at 1 qt of carbaryl for the easiest to thin. He then progresses up to add a quart of oil and further up to add 10 ppm of NAA to the mixture. The rate varies by cultivar and initial fruit set. Not having extensive plantings of any one cultivar and having many different cultivars means we usually end up under thinning some cultivars.

The warm weather expected across the state this weekend will cause a rapid increase in fruit growth. The model predicts out to Monday. However, you should check back if you intend not to thin until Tuesday.

Other Pennsylvania Headlines