Horsenettle (Solanum carolinense), a poisonous member of the nightshade family, is one of the most difficult weeds to eradicate since it resists most attempts at control. Tilling the soil only makes it worse because it brings seeds to the surface where they can germinate. Flame weeding doesn’t kill the weed either because the penetrating roots reach depths of 10 feet or more, where they survive after the tops are burned away. For horsenettle, herbicide is the most practical control method for many gardeners.
Like most seedlings, horsenettle begins life as two small, rounded leaves sitting opposite of each other on a short stem. The first true leaves come as a cluster. Although it still has smooth leaf margins at this point, the plant is beginning to show its true nature because it has prickly spines along the vein on the undersides of the leaves. As they mature, some of the leaves develop lobes and numerous hairs and spines. The stems also develop spines.
In midsummer, star-shaped white or blue flowers bloom. They look like potato flowers, and this isn’t surprising since both potatoes and horsenettle are members of the nightshade family. The flowers are followed by yellow fruit, three-quarters of an inch in diameter.
Frequent mowing is about the only method for the organic control of horsenettle. The roots are at their weakest right after the plant flowers, so let it flower before mowing for the first time. Afterward, continue mowing regularly to further weaken the roots. It can take two years or more to kill the plants this way. To speed things along, however, you can apply systemic herbicides after mowing while the plant is weak.
In late summer or fall, apply an herbicide labeled for use against horsenettle, such as Weed-B-Gone. If you buy a concentrate rather than a ready-to-use product, mix carefully according to the label instructions. The label contains information about how to get rid of horsenettle, and you should read it carefully. Application timing is very important to successfully eradicate this weed.