Color development in apples is a complex process because many factors are involved: genetics, environmental conditions (i.e., light and temperature), nutrition, stress, crop load, etc. Probably some of the most common causes for low red color development in apple orchards are excessive crop load, shaded canopies, and warm fall temperatures. Unfortunately, there isn’t much that we can do to control temperature in the orchards, and if the warm weather trends that we have experienced these weeks in August continue through September (it looks like we will have a warmer than normal September), there might be a delayed in color development.

At this point in the growing season there are a couple of managements that can be implemented to promote red color development. One of them is to use reflective mulches/films under the tree canopy. We recommend placing them about 3-4 weeks before harvest, and if you have narrow trees placing them just on the west side of the row. The other alternative to increase color development is to use plant growth regulators. There are two products that have shown good results in several research trials, Ethephon and Blush.

Ethephon (2 pint/ac) can improve color development when applied 1 week before harvest. Ethephon will stimulate fruit ripening so if applied more than 1 week before harvesting it will increase fruit drop, so be careful! If you are concerned about excessive fruit drop, you can combine ethephon with a preharvest drop product such as Fruitone. Blush, that contains jasmonates, has shown to moderately increase red color development without affecting fruit ripening or increasing early drop. Blush can be applied 2 to 4 weeks before harvest, but best results have been obtained when applied twice, at 3 and 1 weeks before harvest.

This article was posted in Apples and tagged Amaya Atucha, Apples, blush, color, color development, ethephon, jasmonates.