Issue link: https://read.dmtmag.com/i/473131
28 MARCH 15, 2015 GOOD FRUIT GROWER www.goodfruit.com D uring apple thinning time, we need carbohy- drate stress to take excess apples off the trees, but human stress is much less desirable. Fortunately, we can use Precision Cropload Management (PCM) procedures to improve thinning, reduce the risk of over- or under-thinning, and improve our confidence in thinning, thereby reducing human stress and turning tree carbohydrate stress to our advantage. Last year, several Michigan growers used a tool called Predicting Fruitset. This model allows growers to evaluate ongoing fruitset and the effectiveness of their chemical thinning applications. By applying some extra effort during the thinning process, they were able to gain some peace of mind. The growers used a novel approach. They engaged their spouses and children, who teamed up to carry out that extra effort. Start with a target To use PCM, growers first set a target cropload based on anticipated or desired yield, calculating it down to desired number of fruits per tree. Once a target cropload is set, then growers dormant prune to a target budload of, say, 1.5 times the target cropload. If the target cropload is 100 fruit per tree, this means the target budload would be 1.5x or 150 flower clusters per tree. After dormant pruning, the grower chooses five rep- resentative trees and counts the dormant flower buds on each tree. If that is greater than the target budload, they do additional dormant pruning to get closer to the target. Next, at pink stage, 75 flower clusters are marked with flagging ribbon. These clusters will be used to mark and measure individual fruitlets. This is where the growers' spouses and children entered the process. They took the measurements and recorded the data. The individual fruitlets need to be measured two to four times during the fruitset window. Starting at about the 6-millimeter stage, the first measurement is taken to give a baseline diameter. Four to five days later, at about the 8-mm to 10-mm stage, a second measurement is taken, and this will determine each fruitlet's growth and give the first prediction of percent fruitset. Dr. Duane Greene at the University of Massachusetts developed this process after making critical discovery. Fruitlets that will set will grow larger. A fruit will not persist if it is growing at less than half the rate of those fruitlets. After the second measurement, if the prediction is close to the target cropload, then no further measurement or chemical thinning is performed. If the predicted fruitset is too high, a chemical thinner will be applied and another measurement will be taken in four to five days, or at about Stress-free THINNING Crop Management "This project has trained me to see fruitset even before I measure the fruitlets. It has ϔ ϔ taking thinning action." — Bridget Engelsma The model ensures it's the trees that are stressed, not you. by Philip Schwallier and Amy Irish-Brown, Michigan State University Extension Educators PHOTOS COURTESY PHIL SCHWALLIER Michigan growers called upon relatives to help collect data as part of an effort to improve apple thinning. Here Bridget Engelsma, who farms with her father, Jim, at Engelsma Apple Barn, collects data with sister Nicole.