Washington State University scientists hope to find a better way to assess cold hardiness of apple and sweet cherry buds and blooms in early spring.

Crop resistance to freezing temperatures depends on the stage of bud development, and this makes it difficult for growers to know when to protect their orchards. Scientists at the Irrigated Agriculture Research and Extension Center in Prosser plan to develop a cold hardiness model showing the temperatures that buds will tolerate at all stages of development.

Dr. Gerritt Hoogenboom, director of WSU’s AgWeatherNet, is leading the three-year project funded by the Washington Tree Fruit Research Commission.

Current cold hardiness data are based on research conducted more than 30 years ago and with older varieties, reports Melba Salazar-Gutierrez, research associate. These data are still being used today, even for new varieties.

To determine lethal temperatures for buds and flowers, the scientists are using an automated freezer sampler created by IAREC staff member John Ferguson, who also developed a cold-hardiness prediction model for grapes. The machine can hold small cuttings of limbs and flowers and test them overnight, which allows samples to be processed faster than in the past.

The research team began last February by testing samples of Red Delicious, Gala, and Fuji apples, as well as Bing, Chelan, and Sweetheart cherries collected from WSU’s Roza Research Farm and C & M Orchards in Prosser. Samples were exposed to temperatures ranging from -40° to 30°F for varying lengths of time to find out when buds and flowers die. Salazar-Gutierrez said they will continue to collect samples from orchards for two more seasons. They also will study how apple and sweet cherry buds go into ­dormancy.