Using a Section 18 label granted in selected states for use from April until August 2012, Clemson University Researcher Mike Marshall used Brake as an effective herbicide against Palmer amaranth in cotton, providing a potential new tool for growers in the their ongoing battles against pigweed.

Over-use of PPO inhibitor herbicides in areas with high levels of glyphosate resistant cotton is a big concern for cotton growers in some parts of the Upper Southeast.

In many areas of the Southeast these popular herbicides are widely used in other crops that are grown in rotation with cotton.

The growing number of herbicide resistant Palmer Amaranth (pigweed) populations, combined with the fear that resistance problems may occur with over-use of glufosinate and other herbicide families without resistance problems, leaves growers with few herbicide options for over-all weed protection in cotton.

This scenario further accentuates the need for new herbicides with different modes of action, especially for control of Palmer amaranth.

“The big advantage for Brake is that it could be a really good rotational material for Reflex and Valor, two PPO inhibitors that are widely used for weed control in cotton,” Marshall says.

Brake, a product of SePRO Corporation, Carmel, Ind., was given a Section 18 label for use in 11 South Carolina counties in 2012, but the label came with some specific restrictions. The label states, “Brake may persist in the soil past the cotton growing season. To avoid difficulties in establishing rotational crops, the following precautions must be followed:”

• Do not make more than two consecutive applications of Brake. After the second application, use an alternative herbicide effective in controlling the weeds of concern.

Consult your agricultural dealer, consultant, applicator, and/or appropriate state agricultural Extension service representative for specific alternative cultural practices or herbicide recommendations available in your area.

• Apply prior to planting or prior to emergence of cotton;

• Only apply in fields where cotton will be planted both in the year of application, and in the year following application, and not rotated with another crop, unless the following crop rotational restrictions are followed for 18 months — Do not plant grain sorghum, sugar beet, tomatoes and other Solanaceae family of crops for at least 18 months after the last Brake application;

In the Clemson studies, done at the Edisto Agricultural Research and Extension Center in Blackville, S.C., Phytogen 499 was used primarily because it has built in tolerance to both glufosinate and glyphosate, Marshall explains.

In Liberty-based system

In the South Carolina tests Marshall looked at Brake for use in a glufosinate (Liberty) based system for cotton weed control.

In these tests a burn-down  treatment of glyphosate at 22 ounces per acre, plus a pint of 2,4-D was applied on April 22 and cotton was planted in a standard row width on May 22.

Treatments included: 

• Treatment one: Three pints of paraquat plus Brake at 16 ounces per acre at planting. No treatments were used at the 2-3 leaf stage. Glufosinate (Liberty) at 29 ounces per acre, plus Warrant at three pints per acre were applied at the 5-6 leaf stage and MSMA at 2.42 pints per acre and Direx at 1.5 pints per acre (standard rates) were applied at layby.

• Treatment two: Paraquat at three pints per acre, Reflex and Direx, both at one pint per acre were applied at planting. No herbicide was applied at the 2-3 leaf stage. Liberty plus Warrant were applied at the 5-6 leaf stage at 29 ounces per acre and three pints per acre, respectively. MSMA and Direx were applied at standard rates at layby.

• Treatment three: Paraquat at three pints per acre and Brake at 16 ounces per acre were applied at planting. No herbicide was used at the 2-3 or 5-6 leaf stage. MSMA and Direx were applied at standard rates at layby.

• Treatment four: Paraquat at three pints per acre and Reflex and Direx at one pint per acre were applied at planting. No herbicides were applied at the 2-3 or 5-6 leaf stage. MSMA and Direx at standard rates were applied layby.

• Treatment five: Paraquat at three pints per acre and Brake at 16 ounces per acre were applied at planting. Liberty plus Warrant were applied at 29 ounces and 2.7 ounces, respectively, at the 2-3 leaf stage and repeated at 29 ounces and three pints at the 5-6 leaf stage. MSMA and Direx were applied at standard rates at layby.

• Treatment six: Paraquat at three pints per acre, plus Reflex and Direx at one pint per acre were applied at planting. Liberty at 29 ounces per acre and Warrant at three pints per acre were applied at both the 2-3 and 5-6 leaf stages of cotton.

Brake is a bleaching herbicide, with fluridone as the active ingredient.

It is widely used under the trade-name Sonar for control of a number of troublesome aquatic weeds.

Cotton is one of a select few terrestrial plants that will tolerate fluridone, and even so, there will be some significant restrictions, should the material be labeled for use by cotton growers in the Southeast, Marshall says.

On the positive side Brake fits in well with several herbicide programs for controlling weeds in areas with a high concentration of glyphosate resistant weeds and fits well into several glufosinate-based herbicide systems.

In the South Carolina tests, treatments 1, 2, 5 and 6 provided better than 90 percent control of Palmer amaranth from June 13 until Aug. 17.

In comparison, treatments 3 and 4, which contained no herbicide applications at the 2-3 or 5-6 leaf stages provided only 60-70 percent control by Aug. 17.

It is significant, Marshall contends, that treatment 5, which contains no Reflex or Valor, provided 100 percent control of Palmer amaranth from June 13 until Aug. 17.

Since glyphosate is weak in control of annual morningglory, it is also significant that this treatment provided the best (96 percent) control of morningglory during the same time period.

Treatments 1 and 6 also provided better than 90 percent control of both annual morningglory and Palmer amaranth in the South Carolina tests.

Whether or not Brake will receive clearance for use by cotton growers in the Southeast for the 2013 crop remains unclear.

However, tests across the Cotton Belt in 2012, including tests in South Carolina, demonstrated the material is highly efficient as part of a management program to control Palmer amaranth in Liberty-based programs.

rroberson@farmpress.com