| Rodney G. Lym |
| Author is professor, Plant Sciences Dept., North Dakota State University, Fargo, North Dakota 58105. |
Abstract |
| Leafy spurge control with glyphosate [N-(phosphono-methyl)glycine] plus 2,4-D [2,4-dichlorophenoxy)acetic acid] applied annually for 3 years alone or rotated with auxin herbicides was evaluated at 3 locations in North Dakota. Glyphosate applied with 2,4-D averaged 67% leafy spurge control 3 months after treatment which was a 10-fold increase compared to glyphosate alone. Glyphosate plus 2,4-D applied annually for 3 years or rotated with dicamba (3,6-dichloro-2-methoxybenzoic acid) or picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) plus 2,4-D provided 80 to 90% leafy spurge control, which was similar to the standard annual picloram plus 2,4-D treatment but at 30 to 65% less cost. Herbage production was similar regardless of treatment. The absorption and translocation of 14C-2-4-D increased 2- to 3-fold when applied wit glyphosate compared to 14C-2,4-D applied alone. However, both absorption and translocation of 14C-glyphosate was severely reduced when applied with 2,4-D compared to 14C-glyphosate applied alone. The increase in control when glyphosate is applied with 2,4-D may be because sublethal concentrations of glyphosate break root bud dormancy in leafy spurge, thereby increasing the amount of 2,4-D in the root. Glyphosate plus 2,4-D provided good leafy spurge control at less cost than current widely used treatments and should provide a new tool for leafy spurge management. |
| Key Words: dicamba, herbage production, noxious weed, picloram, rangeland weed control |