Every now and then, this weed emerges to remind producers it can be quite a formidable foe.
Tropical spiderwort, also called Benghal dayflower, is a weed that came on the row-crop production scene in the early 1990s and continues to crop up from time to time. Although Palmer amaranth became the weed garnering most of the attention in the last decade, tropical spiderwort never really went away.
As production schemes change, and different herbicide regimes are used, producers will find this weed popping back up in their fields and commanding attention. Because of this, University of Georgia Extension weed specialist Eric Prostko continues to conduct research on management of this weed.
Benghal dayflower is an aggressive weed that produces both above ground and below ground flowers and viable seed. It also possesses the ability to root at the nodes and can be propagated from cut stems. Therefore, light cultivation can often break plant parts and increase the area of infestation.
Although benghal dayflower is difficult to control, early identification and proactive management can greatly reduce its impact on crop yields.
Tropical spiderwort/Benghal dayflower has often been confused with spreading dayflower (Comellina diffusa) and Asiatic dayflower (C. communis). However, three characteristics separate benghal dayflower from the other dayflowers:
▪ Presence of leaf hairs. Dayflower species possess a thick, waxy, leaf that lacks hairs (glabrous). Benghal
▪ Flower color: The flower color of many dayflower species is blue, while benghal dayflower is more purple or lavender;
▪ Root structure: Unlike all other dayflower species, benghal dayflower produces underground flowers. These flowers are easily seen by examining the roots. These flowers will appear as “swollen nodes.”
Current crop production practices, such as minimum-tillage production systems, encourage greater germination and growth of this weed. However, an early observation was that benghal dayflower grows poorly in low-light environments.
Forming a dense peanut crop canopy as quickly as possible can help to suppress germination of benghal dayflower and limit its growth and establishment.
Planting in twin rows is another cultural practice that helps establish rapid coverage of the soil surface and may interfere with weed seed germination and emergence.
In a wet spring, tropical spiderwort tends to be more of a problem. Prostko says that over the years, Dual Magnum has provided some of the most consistent residual control of this weed. The more recently registered herbicides Warrant and Zidua also have good activity on tropical spiderwort.
Prostko says another option is paraquat + Dual Magnum + Basagran or Storm for an excellent early post treatment if the peanut field is still within the labeled paraquat application window of approximately 33 to 38 days after planting.
In another research project, Prostko looked at application methods to determine the most effective means of controlling tropical spiderwort/Benghal dayflower.
“In data collected a few years ago in Grady County it was indicated that postemergence applications were more effective than pre-emergence applications for the control of tropical spiderwort/Benghal dayflower.If growers miss the paraquat application window, the best postemergence treatment for TSW/BD is Strongarm,” Prostko says. “Growers who apply Strongarm POST in peanut need to pay close attention to the labeled crop rotation restrictions.”
Tropical spiderwort is a highly competitive and difficult-to-control weed that will likely reoccur in fields from time to time and will warrant producers’ attention.
Effective control can often be attained if early scouting, cultural and herbicidal management schemes are implemented. In extreme conditions, deep tillage may be helpful, but only if herbicidal and cultural management programs have proved ineffective.