I ran the MaluSim model again today, April 23 (pdf). As you can see from the simulation within the pdf file, we are predicted to have a fairly significant carbohydrate surplus over the next week. This is the result of the forecasted cold temperatures for next ten days.

This data suggests that you can expect an average to below average response from thinning chemicals applied over the next week. In orchards with little to no frost damage, growers may want to increase their rates or add adjuvants, such as oil, to the tank. With the cool weather, fruitlets growth rate has significantly slowed, so there might be another opportunity to thin early next week before fruitlets become too large. Otherwise, orchards that need additional thinning beyond the 12 mm fruitlet size may be treated with ethephon (or ethephon +/- carbaryl +/- oil) up until about 25 mm.

Fruitlets measured at the AREC today were within the size range (8-12 mm) that is typically recommended for fruit thinning:

Empire = 11.7 mm  |  Red Delicious = 10.0 mm  |  Golden Delicious = 8.8 mm

I will continue to run the MaluSim model until chemical thinning is no longer a viable option in the Winchester area.