“Don't ignore yellow nutsedge. Make a reasonable control effort if you have heavy pressure, and the crop will do the rest. Promoting rapid canopy closure will reduce the effect of nutsedge on the crop. Nutsedge even competes with itself. You must consider yield potential and the cost of your control options. If you have high yield potential, you can afford to invest more in controlling yellow nutsedge. If yield potential is low, you'll need a lot of nutsedge to recover your investment.”
Weed control continues to be one of the most costly inputs in peanut production, accounting for approximately 14 percent of all variable costs, or an average of about $50 per acre.
It's one of those production costs that can catch a grower off-guard, says Carroll Johnson, USDA-ARS weed scientist in Tifton, Ga. “Weed control in peanuts can be very expensive. It's been my experience that a grower may start the season with the intention of spending about $50 per acre, but he'll eventually spend from $75 to $100 per acre on weed control,” says Johnson.
Surveys that look at the cost of weed control and the peanut losses associated with weeds show that growers haven't gained much ground over the years, he says.
“We're spending more for weed control in peanuts. A lot of this is due to inflation and increasing costs, but yet we're still having the same losses. At best, we're holding our own. And, you could make an argument that we're losing ground,” says Johnson.
There are several misconceptions regarding peanut weed control, he says. “One of these is that we need more herbicides. We probably did need more herbicides at one time. Now, however, we have a substantial arsenal at our disposal. We always could use new tools, but we already have many from which to choose,” he says.
There were 13 peanut herbicides in 1984 compared to 20 herbicides today, minute that we can't do the job with what we already have — we can.”
A second misconception, notes Johnson, is that new herbicides will save the peanut industry in the Southeastern U.S. “If only our problems were so simple that one herbicide would solve them, but it won't. There is no ‘magic bullet’ or stand-alone herbicide,” he says.
Herbicide developments since 1990 haven't produced a “breakthrough” product that has radically changed peanut weed control, says Johnson.
“We haven't seen a breakthrough that revolutionizes how we control weeds in peanuts. Improvements have been made in certain areas, but new herbicides have been very costly compared to older products.
“Considering recent developments, we've increased the total cost of weed control but we're not making real improvements. We're spending more for weed control, but we're not getting anywhere.”
Most of the newer, premium peanut herbicides are touted to be stand-alone products, but they are not, says Johnson. They usually perform better in combination with other herbicides or sequentially with other herbicides, he contends.
“They do a pretty good job on some species, but they're very narrow in their focus. There never has been and never will be a magic bullet for peanut weed control. The diversity of the weeds and their organisms dictate a broad-spectrum or multi-layered approach.”
Regardless of the herbicide being used, timeliness is critical in controlling weeds in peanuts, he says. “It's a logistical strain on any farming operation to be timely. Timeliness is especially difficult to achieve in a large operation. Often times, this leads to a ‘shotgun’ approach to managing weeds — one weed control program over a multitude of acres, farms or fields.”
Fields many times change hands, says Johnson, and growers will go into a new field not knowing the weed control problems or herbicide use history. “A grower might go back to the shotgun approach and treat for weeds he doesn't have.”
Today's specialized herbicides work very well on some weed species but fail on others, he continues. “A good example is Cadre. It's an excellent, broad-spectrum herbicide, but it won't control tropic croton. It also doesn't do a good job on bristly starbur. Older herbicides like Dinoseb did a good job on just about everything.
“With products that are so specialized, we need to use a more specialized approach when planning for weed control at the beginning of the season.”
In formulating a survival kit for controlling weeds in peanuts, growers first should look beyond peanuts at their entire cropping system, says Johnson.
“Long-term weed control in one crop will help other crops in the rotation,” says the weed scientist. “If you fail to control weeds in one crop, there will be implications for all future crops in that field. It takes about one bad year of weed control to erase about 10 years of good weed control.
“Preventing weeds from going to seed should be the utmost priority in our most productive fields. Fields that are left fallow during the summer can cause weeds to explode due to a lack of crop competition. The benefit of the crop itself often is an understated part of weed control.”
Growers also should know the weed pests in their fields, recommends Johnson. Most growers will have to control the top 10 to 12 weeds found in Southeastern peanut production, he says.
“Nutsedge is troublesome but it's not very competitive. On the other hand, Texas panicum is highly competitive and can cause losses in peanuts. Texas panicum would be the priority weed to control compared to yellow nutsedge.”
It's helpful, he adds, if growers understand the role of weeds, including their weaknesses and life cycles. “Since yellow nutsedge is a perennial, you want long-term, successful control of this weed pest. Anything you can do to target tuber production in nutsedge will pay benefits in the long-term.”
Growers also should match effective controls across all crops, he says, and be aware of thresholds. “We all have an idea of how much trouble a particular weed can cause and when that weed will need controlling. If we go back to the shotgun approach, we'll treat weeds that aren't in the field or that are in low density.”
If a grower ignores a weed like yellow nutsedge — either during one season or through many seasons — it'll cause problems, says Johnson. Under good growing conditions, yellow nutsedge can be effectively shaded out by the crop.
“Don't ignore yellow nutsedge. Make a reasonable control effort if you have heavy pressure, and the crop will do the rest. Promoting rapid canopy closure will reduce the effect of nutsedge on the crop. Nutsedge even competes with itself.
“You must consider yield potential and the cost of your control options. If you have high yield potential, you can afford to invest more in controlling yellow nutsedge. If yield potential is low, you'll need a lot of nutsedge to recover your investment.”
The cost effectiveness of weed control, or getting the most from your weed control dollar, is another important consideration, says Johnson. “You need to squeeze every bit of activity from the herbicide. Do whatever it takes to make the herbicide perform well, including using irrigation to activate the chemical or applying the herbicide to small weeds.”
Integrating cultural with chemical controls also can improve cost efficiency, he says. Stale seedbeds, narrow-rows and conservation-tillage all have been documented as benefiting peanut weed control, says Johnson.
“But the cost of weed control in a conservation-tillage system can kill you if you're not careful. In one trial, the cost of weed control in a conservation-tillage system increased by 400 percent over a five-year period. This is caused mostly by perennial weeds moving into the field.”
It's critical, says Johnson, that growers focus on early season weed control. “Small weeds are easier and cheaper to control than large weeds. The first part of the season is a critical period for competition. If you try to control losses in mid and late season, you've already experienced losses that you'll never recover.”
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