NAA Application In Summer Can Boost Return Bloom

Every year it can be desirable to enhance return bloom on apple varieties that tend to be biennial. This is especially important on trees that have a heavy crop load like Michigan State University researchers are predicting for this year (2013). Most years, treatments of summer NAA applied at five, seven, and nine weeks after bloom will increase return bloom even on varieties that have heavy crop loads and tend to have poor return bloom. This timing is made after the thinning window and any potential thinning from NAA has past. Fruits are often 1 inch in diameter and won’t respond to any NAA thinning action. Flower bud initiation has already begun, but according to Michigan State University Extension it can be enhanced by NAA treatments during the next 30 days after the thinning period ends.
 
Summer Ethrel can also enhance return bloom by treatments of 200 ppm made at the same timing of five, seven and nine weeks after bloom. However, summer Ethrel can thin 1-inch diameter fruit as well as advance maturity of early maturing varieties.
 
A study was initiated in 2000 on biennial varieties. These varieties (Goldens, Jonagold, Paulared, Red Delicious, Fuji Gingergold, and Empire) were treated with three applications of NAA at 5 ppm (Fruitone N). Over seven years on average, return bloom was improved by 23% and some years as much as 55%. These trees were selected because they had heavy crop loads and were not thinned chemically.

To read more on this study, click here.