Better than average soil moisture is likely to increase weed pressure, says a state Extension peanut specialist, increasing the need for early-season weed control. "Herbicides applied pre-plant and at planting have been effective, but new weed flushes following rainfall or irrigation are likely as soil-applied herbicides are dissipating," writes Dr. Emi Kimura, Vernon, Texas, in the Texas A&M AgriLife Extension Texas Row Crops newsletter. "Herbicides applied at early-postemergence that do not have soil activity are also prone to allow new weed flushes. In other words, good early season weed control may need some attention because previously applied herbicides have dissipated over time."
Kimura, Texas A&M AgriLife Research and Extension assistant professor and agronomist, recommends the following herbicides for application now to early peg stage:
- imazapic (e.g., Cadre and other generics)
- imazethapyr (e.g., Pursuit and other generics)
- acifluorfen (e.g., Ultra Blazer and other generics)
- 2,4-DB (e.g., Butyrac and other generics)
- lactofen (e.g., Cobra and other generics)
"There has been some good discussion about herbicides applied to peanuts in bloom to early peg and the potential for increased injury. We have looked at this timing issue with several herbicides, including those listed above, and have not seen a problem when these herbicides are applied at that time during the growing season," says Kimura. "Pay attention to the preharvest interval (PHI) restriction (Table 1)." (Click here for descriptions of these herbicides from the May newsletter article.)
The only herbicide not covered in the May article was 2,4-DB. "Note that 2,4-DB is different from 2,4-D, which is not labeled for use in peanuts. 2,4-D may cause plant death and yield loss, which is dependent on rate and stage of growth at application," says Kimura.
The herbicide, 2,4-DB (e.g., Butyrac 175, Butyrac 200, and other generics), may be used in peanuts at various rates (13 to 28 oz/ac) depending on the formulation, she says. "Applications should be made between two to 12 weeks after planting. Do not apply to peanuts suffering from lack of moisture," she writes. "The second application should not be made later than the late bloom stage of the peanut." This herbicide should not be applied later than 100 days after planting or within 60 days of harvest.
2,4-DB has good activity on several annual broadleaf weeds including morningglory, smellmelon, and sunflower, she says. "This herbicide is also a good option on silverleaf nightshade (whiteweed). The use of crop oil with 2,4-DB will increase herbicide activity; however, crop oil will enhance phenoxy-type injury (Figure 1) to peanuts and cause plants to ‘lay-down’ for 24 to 48 hours," says Kimura. "Plants will recover quickly and research suggests this injury will not result in yield losses at the end of the season." (See Table 2).
Table 2 source: Dr. Eric P. Prostko, University of Georgia, 2015. Rate and application timings used in this study were exaggerated with the intent to causing injury and not recommended timings.
To broaden the spectrum of weed control, 2,4-DB may be tank mixed with other herbicides. "The dominant issue with using 2,4-DB in Texas is cotton injury," Kimura says. "Adjacent cotton fields planted with Xtendflex, LibertyLink, Glytol, and conventional cultivars are exceedingly susceptible to 2,4-DB drift. Effective tank clean-out procedures are very important when the same equipment is used in both peanut and cotton production. It is best to have a separate spray system when 2,4-DB is used."
Peanut herbicide injury symptomology guide: http://publications.tamu.edu/PEANUTS/PUB_peanuts_Peanut%20Herbicide%20Injury%20Symptomology%20Guide.pdf
Texas Peanut Variety website at http://varietytesting.tamu.edu/peanuts/
Emi Kimura, State Extension Peanut Specialist, Vernon, TX
Pete Dotray, Weed Scientist at Lubbock, TX
James Grichar, Senior Research Scientist at Yoakum, TX
Josh McGinty, Extension Agronomist at Corpus Christi, TX