Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Mechanism by Which Ammonium Fertilizers Kill Larkspur

Authors
item Ralphs, Michael
item Woolsey, Lee - NRCS
item Bowns, J. - SUU, CEDAR CITY

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 7, 2002
Publication Date: September 1, 2003
Citation: RALPHS, M.H., WOOLSEY, L., BOWNS, J.E. MECHANISM BY WHICH AMMONIUM FERTILIZERS KILL LARKSPUR. JOURNAL OF RANGE MANAGEMENT. 2003. 56:524-528

Interpretive Summary: Environmental concerns of using pesticides on public lands have greatly reduced the use of herbicides to control tall larkspur. Ammonium sulfate has been reported to control tall larkspur. We determined the mechanism by which fertilizers kill tall larkspur. Ammonium sulfate, ammonium nitrate and common salt were applied at equal salt equivalents to individual tall larkspur plants. There was no difference in mortality between the three treatments, suggesting that it is the salt content that kills tall larkspur not the nitrogen. The relative cost per plant for both ammonium sulfate and nitrate was 12.9¢ and 2.6¢ for salt.

Technical Abstract: Environmental concerns of using pesticides on public lands have greatly reduced the use of herbicides to control tall larkspur (Delphinium barbeyi). Alternative methods of control have used ammonium sulfate placed in the crown of individual plants to kill larkspur. The objective of this study was to determine the mechanism by which fertilizers kill larkspur. The hypothesis was that it is the salt content of fertilizers that kill the plant, not the nitrogen. We applied ammonium sulfate, ammonium nitrate and sodium chloride at equivalent salt concentrations and evaluated their effect on tall larkspur plants. There was no difference between treatments in larkspur mortality. The high rate of all treatments killed greater then 70% lf larkspur plants: ammonium sulfate 400g; ammonium nitrate 264 g; sodium chloride 180 g. We concluded that it is the salt in fertilizers that kills larkspur, not the nitrogen. It is necessary to place the fertilizer or salt in the crown of the plant rather than broadcast it. The relative cost per plant for both ammonium sulfate and nitrate was 12.9¢ and for salt 2.6¢.

Last Modified: 8/19/2014
Footer Content Back to Top of Page