Pennsylvania smartweed has found a way into Mid-South rice fields where a Command-based weed control system is used to combat herbicide-resistant weeds and in some reduced-tillage situations.
The shift to a Command-based weed control system is an evolution of weed management, according to Ronnie Helms, a farmer and partner in G&H Associates, an agricultural research and technical support business in Stuttgart, Ark.
“For years, rice producers sprayed propanil on two-leaf rice, then again pre-flood. They took out a lot of weeds because of the broad spectrum nature of propanil. Smartweed has always been here. But we controlled it with the contact herbicides we used.”
When propanil-resistant grasses emerged in recent years, growers went to other options, including residual herbicides like Command, Bolero, Prowl, and Facet — grass materials which don’t have a lot of activity on smartweed.
That is a big reason behind the emergence of smartweed in rice, as well as hemp sesbania, teaweed, and pigweed.
But there is another factor, according to Helms. “Producers usually like to delay the second herbicide application as long as possible. That means that by the time a pre-flood application is made, any smartweed is at the four- to five-leaf stage and very hard to control. Command may turn smartweed red, but it proliferates in cooler weather.”
Despite smartweed’s unsightliness, it’s still a relatively easy and inexpensive weed to control with proper application timing and chemical choice, according to Helms.
One option is to go with a post-application of Command tank-mixed with other products to control smartweed. “Based on some of our research, we recommend (for Arkansas growers) putting Command postemergence on one- to two-leaf rice with propanil or either Grasp or Regiment. That will take out early emerging smartweed and the Command will give postemergence sprangletop activity. Then in two to three weeks, the farmer can decide about his second treatment based on the spectrum of weeds he has.”
On that second application, “If he has resistance issues, and he doesn’t have any broadleaf weeds, he may need a graminicide like Clincher or Ricestar. If he has resistance issues with propanil or Facet, he could go with the Grasp or Regiment.”
Another mix for broadleaf weeds, if a Command pre-emergence treatment has taken care of grasses, is a Grandstand and Permit tank mix, “which will take out just about every broadleaf there is — joint vetch, coffeebean, yellow nutsedge, smartweed, teaweed, and pigweed.”
Chuck Dallas, a consultant with Jimmy Sanders, Inc., in McCrory, Ark., “picked up a farm late in the season with a 350-acre rice field with about 100 acres in the center of the field infested with smartweed.” He believes the escape may have been due to an application error.
Dallas said the smartweed was controlled with an application of Grandstand, 2,4-D and Permit. “It laid them down.” Next season, he’ll try either Regiment or Grasp. “I’ve seen it in some plots, and I may try some.”
Chris Lockley, a rice producer in Marked Tree, Ark., said, “We’re seeing more and more smartweed every year, because we’re getting away from propanil due to propanil-resistant barnyardgrass.”
Lockley’s consultant, Josh Galleon with Ritter Crop Services in Marked Tree, Ark., said, “In some areas, smartweed was severe, to the point where they would have caused major problems if we had not controlled them.
“But the combination of a good burndown with Valor or Roundup and getting after them early with products such as Regiment and Aim — depending on the weed pressure — controlled them”
Galleon noted that many growers have gone to Command not just to battle resistant grasses, but also to save money. “If you apply Command on time and have the correct moisture, you can control a lot of things, except for broadleaves.
“If you can spend $10 to $13 an acre for Command and possibly get through the entire year if the rain hits right… that’s what everybody wants going to do. We use Command, and then if we have something come up, we take care of it later.”
Next year, Galleon will use two shots of Regiment on fields heavily infested with smartweed. “On fields where smartweed is scattered, I’ll add Aim or Grandstand to whatever I’m using to kill the grasses that come up right before flood.”
Helms advises growers to watch the weed spectrum closely and run two or three active ingredients as a tank mix every time they spray. “You’re going to have good control of most everything you’re after. And it’s also a resistance management program for weed control.”
Mark Kurtz, a research professor at Delta Research Extension Center, Stoneville, Miss., says smartweed hasn’t been a major problem in Mississippi, but it’s troublesome for the few producers who’ve battled it.
“The farmer who has it usually has a serious problem. Those who don’t may not know what it is. It seems to occur in cycles. One year, we may have a terrible smartweed problem, the next year we won’t.”
Kurtz doesn’t believe that smartweed problems are necessarily tied to a Command-based weed control program. “I don’t think that Command is turning smartweed loose. Smartweed is not as much of a problem where fields are worked up in the spring as it is in limited tillage situations, where fields are worked up in the fall and planted in the spring.”
Mississippi growers can address smartweed problems with a burndown program “using either glyphosate or paraquat, and (depending on the smartweed size) 2,4-D can be added.”
An early-postemergence treatment of Grasp “looked better than anything else I’ve seen at that timing, but we’ve had only one trial,” Kurtz said. “Aim will do a good job early, but you have to have small smartweed, 3 inches or smaller. In my experience, nobody ever has small smartweed. When I get a call, it’s usually 8 to 10 inches tall.”
Regiment is a good post-flood option, according to Kurtz. “A lot of growers have battled smartweed with Grandstand or Aim pre-flood. By the time they put the flood on, 8- to 10-inch smartweed is back. I’ve seen Regiment take it out after the flood is put on it. I’ve seen some pretty big smartweed melt down with Regiment.”