By Clint Thompson
How specialty crop growers manage weeds when the field is not being sown is just as important as what fumigant they choose prior to planting season.
Photo courtesy of UF/IFAS
Nathan Boyd, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) associate center director and professor of horticulture/weed science at the Gulf Coast Research and Education Center, has conducted years of research on weed management that shows non-fumigant tactics can be effective.
“We did a lot of long-term trials, three or four years, and the one thing that came out of those trials really loud and clear is what you do to control weeds during the fallow period is more important than what fumigant you decide to use,” Boyd says. “We did different fallow treatments compared to different fumigants. What fumigant you choose can affect weed control, but an aggressive weed management program in the fallow period was just as important.”
YEAR-ROUND MANAGEMENT
Boyd points to nutsedge as an example. “You might get really good control during the crop, but if you let it go during the fallow period, your populations are just going to keep increasing,” he says. “That was true with methyl bromide, even. It was an effective fumigant, but it didn’t get rid of nutsedge.”
Weed control in Florida requires a year-round management strategy, especially for pests like nutsedge. Nutsedge remains a destructive weed that can overwhelm a cropping system and challenge plants for essential nutrients, sunlight and water. It thrives on its ability to penetrate plastic mulches, the common production system that most commercial growers use.
Fumigation is an essential tool in preventing nutsedge from becoming a widespread problem. But fumigation is much more effective when incorporated into a broader management system.
“If you have nutsedge in the field, a combination of glyphosate applications and cultivation alternated is the most effective option,” Boyd says. “The glyphosate is very good at killing the shoots and moving down and killing some of the tubers. Then you’re cultivating again to stimulate another sprouting, so you can hit it again with glyphosate. That’s very effective if your problem is nutsedge.”
Nutsedge is a serious problem where it occurs, but there are many fields where broadleaves and grasses are a problem. A really competitive cover crop can prevent those weeds from growing and producing seed. Boyd says that’s a better option in many cases.
DEALING WITH NEMATODES
Non-fumigant management strategies like cover crops also are effective for nematode control. Johan Desaeger, assistant professor of entomology and nematology at the UF/IFAS Gulf Coast Research and Education Center, recommends sunn hemp as a cover crop to reduce root-knot nematode populations. He believes growers should begin implementing alternative methods of nematode control just in case regulations prevent fumigation use in the future.
“Fumigants are not going to be there forever. It’s hard to put a timeline on it. If you look across the world, the European Union, they’re getting rid of all of their fumigants, and growers have to find a different way,” Desaeger says. “I don’t think much is going to change in the next five years, but after that, who knows? They’re still a good fit for producers, but I don’t think we want to assume they’re going to be around forever. That’s why I’ve been advocating for the need to look for alternatives, more from an integrated approach.”
STILL THE STANDARD
While nematicides and crop rotation are effective control measures, fumigation still has a place in controlling weeds and nematodes for the time being. In most instances, it remains the best method of weed control Florida growers have.
“Pic-Clor 60 in Central and South Florida is the standard. Depending on the season and temperatures, it may or may not do a good job on nutsedge. The response is variable,” Boyd says. “It’s more effective in cooler temperatures than it is in hot summer temperatures, because fumigants volatize quicker in heat and move through the soil too fast. You don’t get the same level of weed control.
“However, that’s nutsedge. In other ratios of Pic-Clor 60 and 1,3-D, they will kill some weed seeds. It’s been documented they can kill various weed species. But, on its own, Pic-Clor 60 does not provide adequate broadleaf grass control if you have significant weed pressure in the field.”
Growers also can add supplemental shallow applications of K-Pam or Vapam fumigant to help significantly with broadleaf and nutsedge control. Vydate is also a viable option for vegetable producers.
“When growers fumigate for nematodes, 1,3-D Telone is really the fumigant that gives the best nematode control. That’s what any grower that has nematode issues is going to use,” Desaeger adds. “In most cases, it’s a mixture of Telone and chloropicrin. There’s not a single thing that’s going to replace Telone by itself. There are the metam products like K-Pam and Vapam that some growers use, which are pretty good. As far as nematode control, I would say they’re decent,” he says.
New nematicides, such as Nimitz, can be applied pre-planting through the drip irrigation system. Desaeger cautions there is a seven-day pre-plant label. Velum Prime fungicide provides effective control of nematodes as well and can be applied through the drip system and on the crop. It is also very safe for growers to use. In fact, the new nematicides are much safer for applicators to use, a point of emphasis for chemical companies in today’s regulatory climate.
“That’s a big benefit in my mind,” Desaeger says.