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In the future, cherry growers might be able to use a degree-day model to calculate exactly when to protect buds from high temperatures in order to reduce cherry doubling the following season.

Doubling is caused by high temperatures sometime during a six-week period when flower buds are differentiating and the flower pistils are going through their initial growth period.

Dr. Matt Whiting, horticulturist with Washington State University in Prosser, who is researching cherry doubling with funding from the Washington Tree Fruit Research Commission, is hoping first of all to pinpoint the critical timing and temperatures that lead to double cherries.

He began the research in 2005, using a tool developed by a colleague with the U.S. Department of Agriculture to either cool or heat the flower bud tissue to certain temperatures. He imposed high temperatures during three two-week periods: the first two weeks of July, the last two weeks of July, and the first two weeks of August. This spring, he compared the amount of doubling in the fruit.

He is also studying the stages of flower bud differentiation and examining buds under scanning electron microscopy to find out at what stage they are most susceptible.

He hopes a degree-day model can be developed so growers can calculate when their flower buds are most susceptible and protect them from extreme heat.

In addition, Whiting is evaluating potential controls that might be used during hot periods to protect buds. These include overtree microsprinklers for evaporative cooling, shade cloth, and sprayable reflective materials, like Surround.

Whiting said doubling can be a serious problem. In a telephone survey, Washington packing houses reported doubling rates of between 3 and 15 percent in the lots of fruit they received. However, the amount of doubling can be much higher in the orchard, with growers reporting as much as 30 percent in some blocks.