Issue link: https://read.dmtmag.com/i/728583
32 OCTOBER 2016 Good Fruit Grower www.goodfruit.com The key lies in combining foliar calcium sprays with reduced potassium fertilization. by Dave Weinstock G rowers have long believed full-season foliar calcium sprays will reduce bitter pit, but two Cornell University horticulture researchers have discovered it's only half the solution: Reduced potassium fer- tilization fills out the rest of the equation. Lailiang Cheng, Cornell University horticul- ture associate professor, and Mario Miranda Sazo, Cornell Cooperative Extension fruit spe- cialist, made this discovery based on ratios of calcium to potassium, phosphorus and magne- sium found in Honeycrisp peels and flesh. This year, for the first time, Miranda Sazo recommended western New York growers reduce their potassium fertilization rather than replenish supplies taken up by the previ- ous year's crop. Based on their findings, lower potassium uptake results in higher levels of calcium in Honeycrisp fruit. "Until now, we have been telling Gala, Empire and McIntosh growers whose orchards produce 1,000 or 1,500 bushels per acre, they needed to apply 70 to 100 pounds of potash (K2O) per acre to replenish what the trees took from the soil," he said. That application is far more likely to set the stage for bitter pit in Honeycrisps. "For Honeycrisp, we may need to lower the (potas- sium application) rate by 25 to 30 percent," Miranda Sazo said. At this point, Miranda Sazo and Cheng are not saying potassium should be brought down lower than that because it is still important to fruit development and sugar accumulation. They are continuing application rate testing this year. Testing is being done in Michigan because its sandier soils hold less potassium. "This allows us to alter the soil potassium level faster," Cheng said. More than just calcium Increasing fruit calcium level by means of foliar sprays still plays a major role in bitter pit mitigation, but it is by no means a panacea. In the early 2000s, Cheng did some research with Dave Rosenberger, Chris Watkins and Steven Hoying using foliar calcium sprays to control bitter pit. "It was effective in some years, but in others, not as effective," Cheng said. One of the things they found was the inci- dence of bitter pit in Honeycrisp is negatively associated with the fruit cortex (flesh) calcium level. "Overall, in a best-case scenario, fruit calcium level explains about 45 to 50 percent of the variation in bitter pit incidence," he said. "In other years, this relationship only explains less than 20 percent." That led them to conclude that there was a lot more to bitter pit than fruit calcium concen- tration alone. In 2006, Cheng's research group did a study of Gala macronutrient and micronutrient requirements. They discovered when calcium was partitioned between fruit and tree leaves, 86 percent of calcium went to leaves and only 14 percent went to fruit. Three years later, Cheng found Honeycrisp leaves had an even higher level of calcium than Gala leaves, and consequently, even lower fruit calcium levels. Based on these two facts, Cheng decided to compare Gala and Honeycrisp in terms of fruit calcium level in balance with other fruit Beating bitter pit in Honeycrisp IFTA New York study tour Mario Miranda Sazo Lailiang Cheng Healthcare WASHINGTON FARM BUREAU Paying too much for health coverage? Call the Washington Farm Bureau today to learn how we can lower your costs. Affordable group health coverage options for you, your family, and your employees Medical I Dental I Vision I Life 800-681-7177 wfbhealthcare.com