Deicing Salts Reduce Cold Hardiness and Increase Flower Bud Mortality of Highbush Blueberry

Injury has been observed since the early to mid-1990s to highbush blueberries ( Vaccinium corymbosum L.) growing along roads in southern Michigan. Symptoms include shoot dieback, flower bud mortality, and reduced yields. To determine if this injury was the result of deicing salts applied to roads, salt (sodium chloride, NaCl) spray was applied to potted blueberry plants, and to the plant root zones. Bushes sprayed six times during the winter with NaCl solutions (0, 0.034, 0.068, 0.137, 0.274, 0.548 m ) developed the same injury symptoms observed in roadside fields, and injury severity was proportional to the spray concentration. The root media of other potted plants was saturated with NaCl solutions (0, 0.017, 0.051, 0.154, and 0.462 m ) in Mar. 2002. Pots were then rinsed with fresh well water when growth began in April to determine if soil salt caused similar damage. The highest soil salt levels killed most above ground growth, and damage diminished with decreasing salt levels. Twigs were also excised from branches sprayed twice with NaCl solutions or water and frozen incrementally to measure the temperature resulting in 50% flower bud mortality (LT 50 ). Salt exposure reduced the LT 50 of flower buds, by as much as 11.5 °C, relative to the control, even within 2 days of treatment. Additional studies with chloride salts (NaCl, KCl, CaCl 2 , MgCl 2 ) and sodium salts (NaCl, Na-acetate, Na 2 SO 4 ) indicated that most reduced the cold tolerance of blueberry flower buds to some degree.