“Liberty-resistance has actually been around a little longer than Roundup Ready. But because of several factors, it hasn’t hit the market yet. The Bayer people are almost promising us we’ll see this technology in 2004,” says Steve Kelly, an LSU AgCenter researcher.
“We don’t use a lot of Liberty in the South like they do in the Midwest with Liberty Link corn and soybeans. What I’m presenting today is just some data to show what these crops are capable of. While the cotton herbicide resistance is great, I’m more concerned about how Liberty will work on southern weeds,” says Kelly, who spoke at the Louisiana Cotton Forum held in Monroe.
Liberty is a broad-spectrum herbicide. It has a killing speed a little slower than paraquat and a little faster than glyphosate. Liberty causes ammonia accumulation within susceptible plants and – as might be imagined – that causes a quick burn.
Kelly says soil microbes rapidly break down the product so there aren’t any soil carryover problems. In fact, Liberty is a synthetically derived product of a soil microbe – making it extremely safe.
“We’ve done some weed control evaluations. Last summer, I planted several weed species and sprayed them with Liberty and Liberty mixes with other products. We looked at two scenarios. One was efficacy on small weeds – typically plants less than 4 inches tall. The second scenario was looking at Liberty on plants up to 12 inches tall.”
Kelly and colleagues planted the weeds with a grain drill and later sprayed the weeds with a backpack sprayer.
On the small test, Kelly planted a wide range of weeds one can expect to see in a Delta cotton field. On the large test, the weeds he planted were the same with one exception – groundcherry.
“What happened is the test field with large weeds used to be in sweet potatoes with a lot of groundcherry. That’s how it ended up in the test.”
On the small weed test, Kelly checked the field 14 days after spraying. On the large test, the field was checked a bit later. The rates used were 24 ounces, 28 ounces, 32 ounces and 40 ounces. The labeled rate on Liberty Link cotton will be anywhere from 28 ounces to 40 ounces per acre.
“We also looked at Liberty plus ammonium sulfate at several rates. Ammonium sulfate is an additive that’s being pushed. I don’t think we need it in Louisiana unless you have hard water, but we’ll look at it a little longer to make sure. Another mix we checked was Liberty plus Staple.”
The “short” test
Among the weeds Kelly worked with in the short test were morningglories, Pennsylvania smartweed and pigweed.
“We got good control of all these weeds when they were small. Prickly sida was controlled very well across all tests.”
Barnyardgrass control wasn’t good with lower rates of Liberty.
“Once we got up to 40 ounces, it was okay.”
Sicklepod control was good – Liberty is very good on broadleaves. Seedling johnsongrass and Palmer amaranth were controlled well.
“Sesbania was controlled pretty well – up to 90 percent control – even with a 24 or 28-ounce rate. We didn’t need Staple added to control sesbania.
“Purple nutsedge jumps out at us. Liberty is not a nutsedge material as it was missed in almost every test we did,” says Kelly.
The “tall” test
The data from tests conducted on taller weeds was collected 19 days after application. Control of morning glories and redroot pigweed were very good.
“Barnyardgrass control was very erratic – we’re going to have another product added to help with barnyardgrass.”
Sicklepod and seeded johnsongrass were handled well by Liberty. Palmer pigweed and sesbania were controlled. Liberty had some trouble with crabgrass – as it had gotten a little bigger than the first test. As seen in the earlier test, Kelly says Liberty had very poor control of purple nutsedge.
“On groundcherry we got 80 percent control when we got into the 40-ounce rate.”
When compared to smaller weeds, control is much more variable when applying Liberty to large weeds. That’s not unusual with any herbicide.
“What we’re seeing with Liberty is if you don’t get the pigweeds when they’re small, it’s trouble. You’ll burn off the terminal and then get some branching and regrowth.”
Kelly says there is no yield data for Liberty Link cotton.
“Unfortunately, no one at the local level has been able to take Liberty Link cotton to harvest because EPA hasn’t fully approved it.
“But cotton tolerance of Liberty is excellent,” says Kelly. “Researchers have applied as much as an 8X rate of liberty and not have any yield loss. This cotton is as tolerant to Liberty as BXN cotton is to Buctril.”
The proposed labeling will probably include a maximum amount of product that can be applied annually.
“Whether it’ll be in the 80-ounce or 120-ounce ranges, we just don’t know. There will likely be two over-the-top applications recommended before first bloom.”
Bayer Crop Science representatives say they are expecting a registration decision from EPA in the first quarter of 2003. If Liberty Link is registered, availability of Liberty Link cotton will be very limited in 2003. Kelly hopes to have some at the university so tests can be run. Liberty Link will be in Fibermax varieties exclusively before moving to other seed companies. There will eventually be Liberty Link/Bt stacked cotton varieties.
What will bring people in or drive them away will be the price of Liberty, says Kelly.
“Right now, Liberty is very expensive – probably twice the cost of Roundup WeatherMax. The company promises to make the price of Liberty competitive, though. We don’t know if there will be a technology fee associated with this product.”