Issue link: https://read.dmtmag.com/i/473131
When the thinner is applied, the model resets pollen growth at zero so that sub- sequent thinning applications can be made to prevent fertilization of blossoms that open later. Second, third, and fourth (if necessary) bloom thinning sprays should occur when the model predicts pollen tubes are no more than 75 percent of the average style length to ensure that fruit are not set in fl owers with short styles. Larson said fi guring out the target crop load is very important, and that process should begin before pruning. "Look at how many potential fl owers you have and the fruit you need on each tree," he suggested. "If your tree's going to have 6,000 fl owers on it and you want 150 apples, you're asking a lot of the model. This process doesn't start the day before you employ the model." To measure the styles, Schell plucks off all the petals from the blossoms and then cuts off the sepals with a knife so he can see the base of the styles and then measures the longest one of each fl ower with a ruler. He emphasized that style length can vary from year to year. "So, you may have one season when your longest style might average 10 millimeters, and the next it could be 14 mm. Just don't assume anything." Adam Zediker, area manager with Washington Fruit and Produce Company, Yakima, said he uses a digital micrometer, or caliper to measure the length and recommends having two people working together, with one person measuring and the other being the scribe. "Two people make it four times as fast," he said. Larson said measuring styles can seem time consuming, depending on how many blocks need to be done, but the manager needs to fi nd people at each ranch to do it. "They pick it up right away," he said. "It's not diffi cult." Schell said he begins measuring styles and counting blooms as soon as bloom begins because it can progress very rapidly. "If you want 60 apples per tree, when that 60th bloom opens up, you'd better start the model." 1RJXHVVZRUN Larson said the model takes some guesswork out of when to thin. "The model is going to tell you when to apply because you've made the decision about how aggres- sive you want to be and how much you want to take off. You've already made those decisions. Once you push the button all you have to do is watch it. You're going to know 12 to 24 hours ahead so you can tell your managers. This is a huge advantage." Larson makes the second and subsequent spray applications when the model shows that pollen tube growth has reached 50 to 75 percent of the length of the style to ensure that they're not applied late and that there's no further fruit set. Zediker said for hard-to-thin varieties he applies the fi rst spray at 80 percent pollen tube growth and subsequent sprays at 50 percent, for the same reason. He said the model helps him to plan and prioritize because he's not making last-minute judgments about when, during bloom, to apply a thinner. "I can collect the data and be in a planning phase, rather than a crisis phase, and I can get across more acres and make better decisions," he said. Zediker has found that pollen tube growth can differ even in blocks that have the same conditions. "If two blocks of different varieties bloom at the same time, using the model, I can make a decision whether to spray the Pink Lady or Gala fi rst, based on the percentage of pollen tube growth that's been achieved," he said. "Once I spray, I can make second, third, and fourth applications and it tells me the time, approximately, that I will achieve the correct amount of pollen tube growth. Then I can manage my sprayers for optimal utilization by selecting the block of highest priority." But Zediker said the model is only as good as the information that goes into it. "Know the blocks and the desired bins per acre before you start the model," he advised. Schell advised growers to try it out on a small block and track what's going on, bearing in mind that it assumes optimal bee activity and pollen availability. Some variability can also be introduced by the differences among pollenizers in their average pollen tube growth rate. "There are no guarantees or absolutes, so you have to be able to take the infor- mation and put it to use in a way that will fi t your orchard and your observations," Schell said. "It did enable me to better time sprays." The model is available for Cripps Pink, Fuji, Gala, and Golden Delicious apples. Models for Honeycrisp, Granny Smith, and Red Delicious are being beta tested and should be released within the next two years, according to Tory Schmidt at the Research Commission. • www.goodfruit.com GOOD FRUIT GROWER MARCH 15, 2015 43 "Know the blocks and the desired bins per acre before you start the model." —Adam Zediker