Q: What weed is this, and how do I get rid of it?
A: The weed in the picture (Figure 1 above) is jimsonweed (i.e. Datura stamonium), a member of the nightshade family. According to the Canadian Poisonous Plants Information System, jimsonweed “contains toxic tropane alkaloids, which have caused poisoning and death in humans and other animals. Jimsonweed is named for a case of human poisoning in Jamestown, Virginia, when soldiers were poisoned by eating the plant in a salad and then suffered delirium and hallucinations. The seeds and leaves are deliberately used to induce intoxication. Children are attracted by the large flowers and become poisoned after sucking the nectar from the base of flowers or ingesting the seeds. Occurrences of human poisoning are more frequent than livestock poisoning in recent literature reports. Animals of all types can be poisoned… Because of the plant’s strong odour and unpleasant taste, animals consume it only when other food is not available.”
As an agricultural pest, jimsonweed is less common but in the last 10 years more farmers have inquired about its control. Jimsonweed is listed as a species controlled on seven herbicide labels (see Table 1 above). Dr. Peter Sikkema has looked at control options in corn and found that many of the soil-applied herbicides provided excellent control six to eight weeks after application (see Table 2 below). Even so, it is not uncommon for farmers to send me pictures of the weed infesting their crops late in the season.
What gives? I speculate it is because jimsonweed has relatively large seeds (see Figure 2 below) and is able to germinate at greater depths, thereby allowing recruitment of new seedlings after a herbicide’s residual activity has dissipated. This is when other methods of control must be identified. There is always the dreaded hand-pulling method, of course, but perhaps inter-seeded cover crops may be helpful in stopping late season germination.