PPDL Picture of the Week

February 23, 2015

ID Weeds in the Field Margins

Travis Legleiter, Weed Science Program Specialist, Department of Botany and Plant Pathology,Purdue University

A great amount of effort has been put towards educating Indiana farmers about the identification of Palmer amaranth over the last couple of years by the Purdue weed science team.  Identification of weed species is critical to formulating a weed control program not only in corn and soybean, but any situation in which weed control is the end goal.  Knowing the correct identification of a weed can help a person understand its biology and allow for alterations of the growing conditions to inhibit the further competition of that weed.  Often we emphasis on scouting for weeds within an agronomic field, but often the weeds on the field margins are of just as much importance.

 

The weeds growing on the field margins or margins of any production area are often overlooked simply because they are not in direct competition with the crop.  These plants are often just as important though, as they are often allowed to produce seed and can quickly go from a species on the fringe of a field to the weed of concern in the field.  In the case of Palmer amaranth, and many other agronomic weeds, these fringe plants contribute a large amount of seed that is easily spread into the field negating any efforts to reduce the seed bank within the field. 

 

This weeks pictures come from southern Indiana along the Ohio River bottoms where producers have been managing Palmer amaranth for a couple of years.  While driving around this area last summer the majority of fields were clean of Palmer amaranth, although along many of the field borders and in the road ditches there was many places where palmer was flourishing.  Again these plants are not in direct competition with the cornfield pictured behind them, but will produce seed the will likely be dispersed into the field.

 

Secondarily, identifying weeds on the field margins can also be beneficial in inhibiting new species from invading the field.  Weeds often begin as plants on the fringe of a field that go unnoticed and then quickly move into the field due to lack of management.  You will also notice in the pictures several other weeds species including hophornbeam copperleaf (pictures alone in pic 3).  Hophornbeam copperleaf is not a weed producers in Indiana often see, but it has slowly made its way north from the Southern United States along with Palmer amaranth.  The plants pictures will continue to grow and produce seed that will likely be at least partially dispersed into the cornfield behind it. 

 

Weed management plans should have a goal of preventing weeds from contributing further to the seed bank; this should include all plants in the production field as well as the field margins.  The next time you scout your fields, make sure you take a look at the field edges as well for any suspicious new species.



​Click image to enlarge

 

Picture 1. Palmer amaranth growing on the margin of a cornfield in Southern Indiana.  Also note the many other weeds species growing around the Palmer amaranth.

 

Picture 2.  A number of weed species growing uninhibited along the edge of a cornfield.  Species include Palmer amaranth, hophornbeam copperleaf, and several others that will likely produce seed that will potential spread into the cornfield.


Picture 3.  Hophornbeam copperleaf is a species that comes from the southern U.S. and can often be found in fields and field margins that have been infested with Palmer amaranth.