ISSUE 13 August 2, 2007
NEW NC EXTENSION PUBLICATIONS
Extension Weed Scientists in the North Central Region have embarked on a plan to develop a series of extension publications on weed management from glyphosate. This includes weeds that are or might become resistant, troublesome, and tolerant in glyphosate systems. The series will also include glyphosate stewardship / management publications.
The following is a list of publications that are available so far.
These publications are housed at a central web site of: http://www.glyphosateweedscrops.org/
Dr George Kegode, former NDSU Weed Ecologist and I just completed, "Biology and Management of Biennial Wormwood". It is not a NC Regional publication in that it seems to only inflict ND but will be an NDSU Extension publication and will be in the same format as the other weed publications.
Hardcopies of these publications, including the Biennial Wormwood publication, can be ordered from the NDSU Extension Distribution Center by emailing Ardis at email@example.com or calling 701 231-7882. External funding sources paid for the printing but there might a slight charge for shipping and handling.
HORSEWEED SEED FACTS
Horseweed, also known as Marestail, is a common weed in North Dakota no-till fields. Many know that biotypes have become resistant to glyphosate in several states in the east and mid-west U.S. A few fact about the biology may help us.
Previous research had found that horseweed seeds may travel up to 1500 ft downwind from the mother plants. This distance of travel could easily move horseweed seed within a field, from a fence line into a field, or from one field in to an adjacent field. However, it would not account for horseweed seed moving longer distances to potentially spread glyphosate resistance.
Researchers in New York and Delaware wanted to determine if horseweed seed was capable of moving long distances in the wind. They described winds in the surface boundary layer, which are 2.5 times the height of the canopy or 15 feet if considering 6 ft tall horseweed. Winds above the surface boundary layer are called the planetary boundary layer (PBL), which generally have greater wind speeds. Winds in the PBL would be responsible for potential long distance seed movement.
To sample the PBL, the researchers flew specially modified RC planes with samplers downwind from a field with mature horseweed over a 3-day period. The 17 30-minute flights were at heights ranging from 128 to 460 ft above the ground. Remarkably, horseweed seed was collected in 13 of the 17 flights regardless of the height of the flight.
As a result of collecting horseweed seed at these heights, the researchers concluded that long distance seed movement is possible. If seeds were blown into the PBL in early afternoon, an 11 mph wind could move the seed 45 to 90 miles. Since winds in the PBL are often greater and frequently may exceed 40 mph, such wind could move horseweed seed over 300 miles. With this long distance dispersal of seed possible, it is also possible for more rapid or wide-scale introduction glyphosate resistant (GR) horseweed.
What might this mean for North Dakota?
Source: Shields, E.J., J.T. Dauer, M.J. VanGessel, and G. Neumann. 2006. Horseweed (Conyza canadensis) seed collected in the planetary boundary layer. Weed Science 54:1063-1067.
NDSU Extension Weed Specialist