P&PDL Picture of the Week for
July 19, 2010

Carolina Horsenettle, More Than a Handful

Glenn Nice, Weed Diagnostician, Department of Botany & Plant Pathology, Purdue University

If you reach down and grab a handful of Carolina horsenettle (Solanum carolinense) you will get more than you bargained for.  Carolina horsenettle is often called simply horsenettle.  This well armed perennial will bite back.  A member of the potato family (Solanaceae), horsenettle is a native to the US that has spines on the stems, petioles and midveins of the leaves.  The flowers have five white to violet petals that are fused into a star shape.  The centers of the flowers are made up of five yellow anthers (the male parts of the flower).  In the late summer horsenettle will produce berries (0.5 to 0.75 inch in diameter) that start out green then turn yellow.  Horsenettle is a creeping perennial meaning that through the use of rhizomes it can spread increasing the number of plants.  Horsenettle can often be found in noncrop and fallow areas, pastures, and occasionally in no-till corn and soybean. 

 All parts of the horsenettle are potentially toxic, but it is the berries that accumulate the largest levels of the toxins. Symptoms are gastrointestinal irritation such as abdominal pain, vomiting, diarrhea.  The central nervous system can be affected inducing depression, apparent hallucinations, convulsions and possibly death.  Removal from pastures and fields is recommended, however this may not be easy.
Control of horsenettle is not easily accomplished.  Regular tillage can wear out the colonies, but infrequent tillage can spread the rhizomes forming new infestations.  Horsenettle is notorious for being hard to control with herbicides. 

The use of 2,4-D alone might provide inconsistent control.  Early work done with 2,4-D reported approximately 80% control[1], however we rated horsenettle control in grass pastures a six out of nine.  In a grass pasture the use of Cimarron Max, Cimarron, Milestone provides excellent control.  Crossbow and Forefront can also be used but can have a slightly lower level of control.  

Preemergence products in corn or soybean have little or no effect on horsenettle.  A control strategy has to be applied postemergence. 

In corn, combinations of products that have the active ingredients dicamba, primsulfuron or nicosulfuron have activity on horsenettle.  These combinations can be found in the product Northstar or by tank mixing Spirit and dicamba together.  Glyphosate also has activity on horsenettle, but use at least a 1.1 lb ae/A rate.  Control was reported using combinations of mesotrione, dicamba, 2,4-D and the primisulfuron; however, the use of 2,4-D or dicamba alone did not adequately control horsenettle.  Control in the whole study ranged from 19% to 92% depending on the treatment suggesting a high level of variation of control.  Using mesotrione plus primisulfuron plus 2,4-D controlled horsenettle 92%, 89%, and 87% in 1999, 2000, and 2001, respectively[1].  The active ingredients primsulfuron, nicosulfuron, and mesotrione can be found in the products Spirit, Accent, and Callisto.  Dicamba and glyphosate can be found in many different products such as Roundup products, Banvel and Clairity.

In soybean, postemergence applications of Classic, Synchrony XP, Pursuit or glyphosate can be used to suppress horsenettle.  Control with these products will be fair (about 70% control).

Reference:
C.R. Armel, H.P. Wilson, R.J. Richardson, and T.E. Hines.  2003.  Mesotrione combinations for postemergence control of horsenettle (Solanum carolinense) in Corn (Zea mays).  Weed Technology Vol. 17:65-72.

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Horsenettle

Horsenettle flower

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service