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Title:	Does Paraquat Cause Stem Swelling in First-Year Cottonwood Saplings?
Author(s):	Leininger, Theodor D.; McCasland, C.S.
Date:	1998
Source:	USDA Forest Service Southern Research Station Asheville, North Carolina June 1998. General Technical Report SRS-20.pp 44-48.
Description:	Abstract-This study was prompted by the occurrence, in 1995, of stem swellings on about 80 to 90 percent of all first-year shoots of eastern cottonwood (Populus deltoides J. Bartam ex Marsh.) after an application of paraquat to control weeds in a 65-hectare plantation near Fitler, MS. Paraquat was applied in spring and summer 1996, respectively, to the bases of two different sets of first-year cottonwood saplings at 0, 0.25, 0.5, 1 .O, and 2.0 times the normal rate used for weed control to determine a dose-response relationship for paraquat and the occurrence of stem swellings. The occurrence of swellings 2, 3, and 4 months after the spring treatment was positively related to paraquat dose. Swellings occurred less often, and only at the 1 .O and 2.0 rates, after the summer treatment. Sapling survival was related to paraquat dose for the spring application ranging from 97 percent in the control group to 18 percent for saplings treated with the 2.0 rate. Paraquat dose did not affect sapling survival after the summer application. Four months after the spring treatment, stem diameters of saplings treated with 1 .O and 2.0 rates were 67 and 38 percent, respectively, of those of the control saplings. Stem heights showed similar responses. Summer treatments had little effect on diameters and heights of saplings. Use of paraquat to control weedsin first-year cottonwood plantations should include provisions to reduce or eliminate contact with green stem tissues.
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