It's a fact that broadleaf weeds rob corn and sorghum of necessary nutrients and moisture. But the use of atrazine, one of the preferred and effective herbicides for broadleaf weed control, has led to runoff problems affecting neighboring watersheds in Texas — threatening sources of public drinking water.
A joint study by Texas Cooperative Extension and the Texas Agricultural Experiment Station suggests farmers can incorporate one of two methods into their planting programs to avoid runoff, resulting in higher yields that will help offset the additional costs.
One concept calls for concentrated applications of atrazine directly over planted rows, called banding. Weeds in the middle of rows are then controlled mechanically with early season cultivation.
Another concept, called incorporation, can be implemented as a pre-planting method that also reduces the threat of atrazine surface runoff after rainfall.
What's most pleasing to farmers is either method can lead to higher yields — helping cover additional production costs associated with the banding or incorporation methods.
“Several (Texas) water supplies have detected trace amounts of atrazine in finished drinking water,” said Monty Dozier, Extension water quality specialist. “The source of this atrazine in Central Texas has been linked to atrazine surface runoff coming from agricultural production areas and urban landscapes.”
Dozier has been working jointly with Dr. Paul Baumann, Extension weed control specialist, and Dr. Scott Senseman, director of the Experiment Station Pesticide Fate Research Laboratory.
The group wanted to look at atrazine application methods and find a way to allow producers to keep using atrazine, yet reduce off-target losses of the product in surface runoff.
“If you take atrazine away, you could affect corn yields and drive up the cost of production by as much as $10 an acre,” Dozier said. “We wanted to try and find a way that would allow producers to keep atrazine in their tool box.”
Experiments were conducted at the Stiles Foundation Farm in Thrall and at the IMPACT Center in College Station — each location having different soil types. Typically, farmers apply a broadcast spray over the entire field and let rainfall incorporate it into the soil.
But Extension and Experiment Station researchers evaluated “pre-plant incorporation (ppi)” applications of atrazine where the product was mechanically incorporated 2 to 3 inches deep immediately after application and prior to planting the crop.
“Instead of waiting for rain to incorporate and activate the herbicide in the soil, you accomplish this through the use a rotary hoe, spring-tooth harrow, field cultivator, ro-terra or some other implement,” Dozier explained.
Researchers also evaluated “banded” applications of atrazine where it's applied in a 13-inch wide band over the top of the planted row after planting. Weeds in the middles were then controlled mechanically with early season cultivation.
Each method was replicated four times. For each application method, the percent of weed control, final corn grain yield, and the amount of atrazine lost in surface runoff were evaluated, Dozier said.
“PVC tubes were placed into the ground at the end of the rows on a 2 percent to 4 percent slope to collect any naturally generated surface runoff,” Dozier said.
Inside each PVC tube was a check valve with a ball that floated to the top of the valve as the PVC tube filled with runoff water. Once full, the ball sealed off the tube from any additional surface runoff.
“It's what we call a passive-type collection system,” Dozier said.
In 2000, the first experiment was conducted. Follow-up experiments were completed in 2001 and 2002.
“The neat thing was that at each site it was the same story,” Dozier explained. “We were able to reduce off-target losses of atrazine from the incorporated and banded methods compared to the more traditional broadcast surfaced-applied method. We never had a change in that trend.
“What we always look at is the first runoff event after application. The first flush (first rainfall) is when we lose the largest percentage of surface-applied herbicides. If we can keep the atrazine on the application site after that first initial flush, chances are we can keep it in place where weed control is needed.
“Producers get better weed control and the public water suppliers get less off-target atrazine moving into their water supplies.”
Currently nine lakes and one river in North Texas are being monitored by the Texas Commission on Environmental Quality for atrazine oncentrations. Much of the focus has been on Aquilla Lake, which serves as the source of drinking water for Hillsboro and other nearbycommunities.
If the use of atrazine were to be banned, farmers could expect to pay as much as $9.20 per acre more to produce corn and $6.50 more per acre for grain sorghum. The results from this effort indicate farmers can reduce the amount of atrazine running off from their corn fields while not sacrificing weed control or yield.
This would lead to an increase in net returns per acre, Dozier said, based on the cost of the herbicide and the application and additional tillage operations for both the banded and incorporated methods compared to the broadcast method.