The Park brothers have decided they are no longer going to be held hostage by Palmer amaranth. Ronnie and Nelson Park, Mount Olive, N.C., have adopted a zero tolerance for pigweed. And says Ronnie, “We appear to be making some progress.”
They start with what they think is the best herbicide program they can devise for their wheat-soybean, cotton and grain sorghum farming operation. But they still consider one non-chemical control measure essential: the manual removal of escapes.
“We’ve been aggressively hand pulling pigweeds for seven years now,” says Nelson, “and it has definitely helped us reduce the seeds that are left after harvest. There have been fewer and fewer pigweeds to pull every year. This works because the best time to get pigweed is while it is still in the ground. We pull any escapes we find — even if it is late, we try to get them.”
That doesn’t always appear to be cost-efficient, but the Parks pull them all anyway.
“It will benefit you next year because you won’t have them to deal with,” says Ronnie. “If you don’t pull that weed this year, you’ll see its brothers, sisters and cousins next year.” (A female Palmer amaranth plant can produce 250,000 to 300,000 seed.)
In 2012, the Parks assigned the removal task to one worker, and that seemed to work pretty well. But, it’s a tough job: Late-season pigweeds don’t normally lend themselves to chopping with a hoe, so one has to grab hold and pull to get them out.
“They hold in the soil, so getting them out is hard enough,” says Ronnie. “But even worse is that pigweed has sharp thorns and attracts fire ants — it’s not easy work.”
As difficult as hand removal is, the Parks can point to clear visual proof that it works. They have one soybean field that butts right up against a neighbor’s bean field. The neighbor has never hand-removed pigweed, and in September his field had numerous tall pigweeds while the Parks’ beans had none.
When Arkansas scientists took one highly-infested field and subjected it to a zero-tolerance program, where the goal was no escapes, hand chopping required 100 man hours, says Ken Smith, Arkansas Extension weed scientist. The next year, only five hours of hand chopping was needed.
“We can get it down to a manageable level,” he says.
Larry Steckel, Extension row crop weed specialist at the University of Tennessee, says, “You may well be able to destroy a lot of weed seed by managing weeds after harvest. This may mean you have fewer to manage next year. If you get to it while the pigweed is still flowering, the results can be good.”
Shading with a cover crop is another non-chemical method that could give pigweed control a boost. “If we can get the ground shaded with a cover crop early on, we can curtail how many weeds we may have to fight with our herbicides later on,” Steckel says.
There are three things pigweed needs to germinate, he says:
“Water and heat are obvious. The third is light. We have a lot of work now showing that light promotes germination of pigweed. So, if you have a good cover crop, you are going to really cut down on how many pigweed seeds germinate.”
Steckel and other scientists have looked at various rotations.
“We found that wheat double-cropped with beans actually does a pretty good job,” he says. “A good wheat stand seems to shade out the pigweed coming up early, and then you’re well on your way toward control without relying on herbicides. That could be a big plus.”
But the wheat stand has to be good. He tells of a farmer following this approach who had a thin stand of wheat. The pigweeds broke through.
Eric Prostko, Extension weed specialist at the University of Georgia, suggests that a dense cover crop of rye, planted in the fall, terminated at its maximum height and rolled, will form a residue mat so thick it will provide from 60 percent to 90 percent control of Palmer amaranth.
Deep plowing is another option, he says. “Not everyone wants to plow — but if you bury pigweed seed deeper than four inches, it’s not going to come up. We have gotten 50 percent control in peanuts just from plowing.”
In Georgia, there seems to be some misinformation about the effect of shading by the cotton plant, says Stanley Culpepper, Extension weed scientist.
“Many growers think pigweed can escape after the cotton canopy closes. If you lay-by with a sound herbicide program in a timely fashion, weeds generally will not emerge after cotton canopy closure. This is rarely if ever a problem.”
Others think that pigweed comes up after lay-by, he says, but more often, that is not the case. “If you have escapes, that means the weed was not killed at lay-by — perhaps because the application was too late, or you had poor coverage, or you used the wrong herbicides — and those surviving plants then made their way through the canopy.”
A sobering note: The era of total postemergence weed control appears to be over, says Tennessee’s Steckel. “And I don’t think it’s ever coming back. I often tell our growers, ‘Think back to 2002 and 2003. You’re going to think of that as the good old days, because weed control is never going to be that easy again, or simple, or cheap.’”