Rhubarb stalks exposed to frost can become toxic
The Daily Ledger (Illinois)
A Canton woman was cited as reporting Friday her grandmother fell ill Wednesday after eating cake made with rhubarb stalks that had been exposed to frost this spring after emerging. Her grandmother was taken to the hospital and diagnosed by a local doctor as having rhubarb poisoning. The story says that the ailment had to run its course for the older woman to recover.
It has often been reported that rhubarb leaves are toxic. Dangers posed by rhubarb stalks exposed to frost seem less familiar. Thanks to the Canton woman who called Friday, the following research was faxed to the Daily Ledger. The information was attributed to University of Illinois Extension-McLean County.
Tony Bratsch, Extension horticulturist at the Effingham Extension Center, was cited as saying rhubarb is a popular vegetable grown for its leaf stalks which are very tart and sought after for making jams, jellies and especially pies. The leaves are very large and showy in the garden but are inedible due to oxalic acid and oxalic content which can cause poisoning.
Given the late hard freezes in the area this April, there has been damage to rhubarb plantings across the state. Rhubarb emerges early in the spring, and frost or hard-freeze damage is a common occurrence. Gardeners can take some steps to protect plants by covering them. However, although floating row covers, sheets, blankets, straw or tarps provide some degree of insulation, once temperatures fall to a range of the lower to middle 20s, these protective covers reach their limitations, Bratsch says.
"In response to freezing temperatures, the oxalic acid in the leaves will translocate (move) to the rhubarb stalk. Once frozen, the leaf tissue will initially appear 'water soaked' and then wilt, and eventually blacken along the edges or where tissue was damaged. Once the plant experiences a damaging freeze, the stalks should not be eaten, and should be removed from the plant.
"Eventually a new set of leaves will emerge, and no permanent damage is done to the plant. A mature plant should yield another crop of stalks within four to six weeks," Bratsch explains.
The report, "All about Rhubarb! (And Frost to it!)" offers further information about rhubarb and is available on the Web (http://web.extension.uiuc.edu/mclean/news/news6179.html).
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