– Christine Gelley, OSU Extension Agriculture and Natural Resources Educator, Noble County (originally published in The Ohio Cattleman)
Horsenettle is often unnoticed until mid-summer!
Prickly, pesky, pests are common among weed species that can become established in Ohio pastures and hayfields that can be challenging to respond to. Two that cause frustration include cocklebur and horsenettle.
Cocklebur is a summer annual weed from the Asteraceae (daisy/sunflower) family. Unlike many of its relatives, cocklebur looks nothing like a daisy. The mature leaves of the plant look similar to the leaves of a sycamore tree, with irregularly lobed and toothed leaf margins. The flower it produces is usually unnoticed because it is green. The fruit it produces is a cluster of egg-shaped burs that easily catch on and hitch a ride on the hide of animals that pass by. Cocklebur can be especially damaging to animals with fiber value.
Horsenettle is a member of the Solanaceae (tomato) family. It’s leaves and flowers are similar in appearance to tomatoes, except the leaf midvein on the underside of the leaf is lined with sharp spines. The berries of the plant will appear similar to yellow cherry tomatoes when mature. Although they look safe to eat, they are not. While all parts of the plant can be toxic, the berries are most problematic. Horsenettle is an opportunistic and persistent perennial plant.
To learn more about identification of cocklebur, you can visit the OSU Weed Management website at: https://u.osu.edu/osuweeds/weed-id/broadleaves/sunflower-family/common-cocklebur/
To learn more about identification of horsenettle, you can visit the Ohio Perennial and Biennial Weed Guide at: https://weedguide.cfaes.osu.edu/singlerecord.asp?id=55
You can also search YouTube for “Forage Focus Horsenettle” and “Forage Focus Cocklebur” for short videos on identification of both these weeds.
Commonly these plants pop up in the paths that animals travel to reach a common feed, water, or mineral access point, where desirable grasses and legumes are unable to persist. They thrive in disturbed soils with full-sun and good fertility.
Cocklebur has become more prevalent in recent years.
Neither plant is appealing from a grazing perspective due to the hairy leaves and prickly plant tissue, but extremely hungry animals or those without grazing experience may be tempted to taste them. Poisonings are more common when the plant tissue is unavoidable in hay. Although the drying process of haymaking reduces the toxins present in the plant tissue, they are not eliminated.
The most common situations where animals are poisoned by toxic plants are a result of management decisions that lead to inadequate access to enough good forage to eat. Overgrazed pastures or forced feeding of hay containing toxic plants are more often the cause of a poisoning than the plant itself. The amount of plant material that must be consumed to create a negative reaction depends on the species, age, and stage of the animal and the plant.
While many producers hope to address weed challenges with strategic clipping of pastures, mowing is not very effective for cocklebur or horsenettle. This is due to their ability to flower and produce seed so low to the ground. Tillage can be a tempting practice to implement for control, but it will often stir up additional weed seed that is lying in wait in the soil bank.
Herbicides containing aminopyralid, clopyralid, 2,4-D, dicamba, metsulfuron methyl, triclopyr, and/or glyphosate are generally effective either as broadcast sprays or targeted sprays for cocklebur, but horsenettle is susceptible to fewer herbicides. Aminopyralid, metsulfuron methyl, triclopyr, and glyphosate provide 80 percent or better control on horsenettle.
Outside of herbicide application, planting a summer cover crop may provide enough competition to smother both of these weeds by creating shade and utilizing water and nutrients more effectively. This may be best accomplished with the use of a no-till drill to seed an annual grass species, such as sorghum-sudangrass or grazing corn. Multiple growing seasons of this practice may be required before a noticeable difference is seen. Keeping up with soil fertility should always be a priority as well to allow desirable plants to thrive and reduce the window of opportunity for harmful plants such as these to establish.
If you are noticing heavy weed pressure by cocklebur or horsenettle, I encourage you to take action to address it sooner rather than later. Additional control details are available in the OSU Weed Control Guide, which is available as a spiral bound book or downloadable PDF from OSU Publications through your local Extension Office or online at: https://extensionpubs.osu.edu/category-2c-agricultural-weed-control/