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Unruly Arundo donax Targeted by Weed Experts

From California to Maryland, a streamside invader called giant reed or giant cane is crowding out native trees like alders, cottonwoods and willows. Known to scientists as Arundo donax, this member of the grass family sports feathery white plumes called panicles and can grow 3 to 7 inches a day, reaching 30 feet in height.

But little is known about the biology and ecology of this aggressive weed, according to Agricultural Research Service ecologist David F. Spencer at Davis, Calif. He is with the ARS Exotic and Invasive Weed Research Unit.

Spencer and ARS technician Greg G. Ksander, also at Davis, are developing equations that predict this troublesome plant's growth at various times of its life under various environmental conditions. During some of these stages and climatic conditions, the weed may be particularly vulnerable to control tactics, such as spraying it with herbicides or unleashing beneficial insects to attack it, Spencer noted.

Fish and wildlife specialists, water-district managers and other streamkeepers throughout the United States can apply the data derived from the equations. That will help them pinpoint the timing that makes the best use of herbicides, biological control insects or other tools to battle Arundo.

In one experiment, Spencer and Ksander are determining how specific temperatures affect the plant’s ability to sprout. They found that cuttings of aboveground stems and thick underground stems called rhizomes, kept indoors in temperature-controlled growth chambers, sprouted at 57 degrees F or 68 F. At 45 degrees F, no shoots grew from rhizome sections. At that temperature, only a single shoot sprouted from a stem cutting, but soon died.

Results from tests with rhizomes that the researchers planted outdoors at Davis showed that shoots first appeared in late March, when the average weekly temperature was 53 degrees F. New shoots continued to emerge until November. The scientists will work this new temperature data into equations that relate sprouting to temperature and to number of days elapsed.

ARS is the U. S. Department of Agriculture's chief scientific research agency.