Is 2,4-DB Still A Viable Option?

Does the control it offers outweigh the injury to the crop?

  2,4-DB:
 

• Good activity on several annual broadleaf weeds

• Only option when weed size exceeds label recommen- dations of other herbicides

• Best option to achieve perennial weed control

• No yield or grade reductions at normal rate

• Expect some foliar injury or “canopy wilt”

• Drift destructive to cotton

• Reduce cross contamination by cleaning spray equipment thoroughly

We have experienced some challenging weed management environments over the past several years. Below average rainfall, triple digit temperatures and conditions too windy to fly a kite have put our herbicides to the test in recent years.

One of the keys for successful weed management is early season control. Peanut fields must be kept clean for the first four to six weeks after planting in order to maximize yield. This can be accomplished with the use of preplant burndown herbicides or tillage before planting, preplant herbicides (Prowl, Sonalan, Treflan) followed by mechanical incorporation or irrigation, preemergence herbicides (Valor, Dual Magnum – also sold as Parallel, and Strongarm in labeled areas), and Gramoxone Inteon (also sold as Firestorm, Parazone) from ground crack to 28 days after cracking.

Full Season Options
We typically see weeds start to break through preplant and preemergence herbicides between four and eight weeks after application, and growers may need additional weed management strategies in order to achieve full-season weed control. Several herbicides are labeled for use postemergence in peanut. Basagran has activity on common cocklebur, sunflowers and yellow nutsedge. Ultra Blazer and Cobra are effective at controlling Palmer amaranth (carelessweed), annual morningglory and other small-sized annual broadleaf weeds.

Weed efficacy from these herbicides will quickly decrease as weed size increases, and these herbicides do not provide residual weed control. Storm, a prepackaged mixture of Basagran and Blazer, may be used to control a wide range of small and actively growing annual broadleaf weeds. All of these postemergence herbicides need a spray additive, or crop oil, for maximum herbicidal activity against weeds.

In general, these herbicides are effective on a broad spectrum of broadleaf weeds that are up to four to six inches in height. Dual Magnum and Outlook may also be used postemergence for yellow nutsedge control. To effectively control yellow nutsedge with Dual Magnum or Outlook, the yellow nutsedge must be less than 10 inches in height, and irrigation or rainfall amounts of at least 0.5 inch must follow the herbicide application within 24 to 48 hours to move the herbicide into the root and tuber zone of yellow nutsedge plants.

Applying Dual Magnum or Outlook postemergence also decreases the potential of crop injury following preemergence applications.

Herbicide options to control early season grass weeds include Select (also sold as Arrow, Shadow) and Poast Plus. Cadre (also sold as Impose) and Pursuit have good activity on many broadleaf and grassy weeds, as well as both yellow and purple nutsedge. Also, both of these herbicides have an 18-month rotation restriction following application before cotton and grain sorghum may be planted.

Resistance to Cadre and Pursuit has become a bigger concern across the peanut belt over the past few years. Susceptible weeds that appear more and more tolerant year after year may be a sign that weed resistance may be present. The use of herbicides with different modes of action is critical to delay and/or prevent the development of herbicide-resistant weeds.

Effect On Yield And Grade
Phenoxyacetic acid herbicides (e.g. 2,4-D) are phytotoxic to both broadleaf weeds and crops. However, 2,4-DB (Butyrac or Butoxone), a phenoxybutanoic acid, is an inactive herbicide and must undergo beta oxidation (the removal of two carbons from butanoic acid to render acetic acid) to be activated.

Leguminous crops, such as peanut and soybean, have low beta oxidase activity, which prevents the rapid conversion to 2,4-D. Additional 2,4-DB tolerance is achieved because of the combination of reduced-spray retention and translocation and less effective absorption.

Injury to peanut with 2,4-DB is a concern to many growers, especially during reproductive periods. One report in 1978 on a Spanish peanut variety indicated that a single application of 2,4-DB from maximum pegging to early pod enlargement reduced both yield and grade and resulted in enlarged pods. This study, however, was conducted at twice the labeled rate of 1.6 pints per acre.

In later work, Grichar et al. (1997) reported in south Texas that runner-type yield and grade was not affected by 2,4-DB during all stages of development from pre-bloom through early pod development. Baughman et al. (2002) reported that Virginia-type peanut yield, grade and pod and seed weight were not influenced by 2,4-DB when applied to peanut from pre-flowering to pod maturity.

Expect Injury And Effective Control
Dotray et al. (2004) reported that peanut yield and quality (including enlarged and misshapen pods) were not affected by 1.6 pints of 2,4-DB with and without crop oil applied at application timings from pre-bloom to pod maturity in two runner-type varieties. In this study, applications were made one time at 30, 60, 90 and 120 days after planting (DAP) or in sequential applications (30 followed by 60, 90 or 120 DAP; 60 followed by 90 or 120 DAP; and 90 followed by 120 DAP). Visible injury was noted following all 2,4-DB applications regardless of application timing and use of crop oil, but no injury exceeded five percent.

The visible injury on leaflets with 2,4-DB is quite common and may consist of elongated leaflets that may have a slightly faded appearance. This symptomology is not visible on new growth and will usually remain visible on lower leaves throughout the growing season.

The application of 2,4-DB can be applied alone or accompanied by a crop oil concentrate. Many growers use a crop oil concentrate such as Agridex with 2,4-DB to increase efficacy against taller weeds. However, adding Agridex to 2,4-DB increases herbicide uptake in both weeds and in peanut, and peanut will “lay down” for two to three days after this application.

  2,4-DB: The Economical Choice
 

2,4-DB: The Economical Choice
What about in the Southeast and Virginia-Carolina area? Is 2,4-DB still an option for growers in these production areas? Weed management experts from those areas weigh in.

“Yes, it is inexpensive, controls several weeds on its own and makes many of the other broadleaf herbicides perform more effectively,” says David Jordan, North Carolina State University Extension agronomist. “There are certainly other herbicides that are more broad spectrum than 2,4-DB, but for the money and the help it gives, it may be the most economical herbicide we have.”

Jordan says many growers in his area, probably over three quarters, make at least one application per year, and many also make two applications.

“Next to grass herbicides like Poast or Select, this would be a postemergence herbicide I would hate to not have for peanut weed control,” he says.

Helps Other Herbicides Do More
Jason Ferrell, University of Florida Extension weed specialist, agrees that 2,4D-B definitely has a place, and is particularly important in helping other herbicides kill a lot more weeds.

“For example, Gramoxone alone is a good product, but will generally miss morningglory and sicklepod. If you put in a few ounces of DB, these weeds will disappear.

“Same way with Cadre,” he says. “If you are spraying an area that has larger than normal morningglory, sicklepod or hairy indigo, DB will definitely help. It might not totally kill the weeds, but it will generally mess them up bad enough that the crop can overtake them.” PG

A Different, Needed Mode Of Action
So is 2,4-DB still a viable option in a peanut weed management program? We think so. This herbicide has good activity on several annual broadleaf weeds including pigweed and morningglory species, smellmelon and sunflower. This herbicide may be the only option when weed size exceeds label recommendations of other postemergence herbicides.

Perennial weed control (e.g. silverleaf nightshade) may only be achieved with the use of 2,4-DB or tankmix combinations containing this herbicide.

Weed resistance to Pursuit and Cadre must be managed by alternative “modes of action,” of which 2,4-DB would be a viable option. 2,4-DB is an effective tank mix partner for many broadleaf herbicides in peanut, but it does come with some serious risks.

The main concern over the use of 2,4-DB in west Texas is cotton injury. Adjacent cotton fields are extremely susceptible to 2,4-DB drift.

Tank contamination is another serious concern when the same equipment is used in both peanut and cotton production. Care must be taken to rinse out spray tanks and equipment with plenty of water to rid the spray system of 2,4-DB. Ammonia may be added to the rinse to reduce the likelihood of 2,4-DB carryover. We recommend a separate spray system when phenoxy herbicides are used in a crop production system that contains crops susceptible to these herbicides.

An old timer a few years ago said that it is best to apply 2,4-DB and not look at your peanuts for two weeks, so they have had a chance to recover from the initial application. Another said that the initial “canopy wilt” may help in the pegging process. Regardless, expect some 2,4-DB induced symptoms in your peanut field after application and expect effective weed control. Always read and follow label directions before using any pesticide.

PG