Field experiments were conducted at nine locations in Texas and Georgia in 2005 and 2006 to evaluate peanut tolerance to lactofen. Lactofen at 220 g ai/ha plus crop oil concentrate was applied to peanut at 6 leaf (lf), 6 lf followed by (fb) 15 days after the initial treatment (DAIT), 15 DAIT alone, 6 lf fb 30 DAIT, 30 DAIT alone, 6 lf fb 45 DAIT, 45 DAIT alone, 6 lf fb 60 DAIT, and 60 DAIT alone in weed-free plots. Lactofen caused visible leaf bronzing at all locations. Yield loss was observed when applications were made 45 DAIT, a timing that would correspond to plants in the R5 (beginning seed) to R6 (full seed) stage of growth. At all locations except the Texas High Plains, this application timing was within the 90 d preharvest interval. Growers who apply lactofen early in the peanut growing season to small weeds should have confidence that yields will not be negatively impacted despite dramatic above-ground injury symptoms; however, applications made later in the season, during seed fill, may adversely affect yield.
Peanut (
Peanut has several unique features that contribute to challenging weed management. First, peanut produced in the United States require a fairly long growing season (140 to 160 d), depending on cultivar and geographical region (
Control of annual grasses and small-seeded broadleaf weeds can be achieved with a dinitroaniline herbicide applied preplant incorporated (PPI) (
Lactofen was registered for use POST in peanut in 2005 for control of several annual broadleaf weeds including annual morningglory. Lactofen is classified as a diphenyl ether (cell membrane disruptor) which interferes with protoporphyrinogen IX oxidase synthesis and causes accumulation of protoporphyrin IX (
Peanut and soybean (
Field experiments were conducted at four locations in 2005 and five locations in 2006. Locations included Lamesa (Texas High Plains, 2005–06), Lockett (Texas Rolling Plains, 2005–06), Yoakum (south Texas, 2005–06), Ty Ty (Tift County, GA, 2005–06), and Plains (Sumter County, GA, 2006). The experimental design was a randomized complete block with three or four replications depending on location. The plot size was two or four rows by 7.6 to 9 m. Lactofen at 220 g ai/ha plus crop oil concentrate
Planting, application, and harvest dates; and peanut cultivar used at 9 locations in Texas and Georgia in 2005 and 2006a.
All data were subjected to mixed models. Data were analyzed using the PROC MIXED procedure of SAS
Peanut injury from lactofen was characterized as small necrotic lesions and leaf bronzing. This injury was evident for several weeks after application on tissue that intercepted the herbicide at the time of the application. Subsequent new growth did not show the effects of the herbicide, but in severe cases plant stunting occurred. Visual injury was assessed from zero to eight times depending on locations, so injury was analyzed separately by location.
In 2005, lactofen applied at 6 lf injured Tamrun OL02 15 to 18% when evaluated on Jun 17 (17 days after treatment, DAT), 25 to 28% when evaluated on Jul 15 (45 DAT), and injury was still apparent late-season (6%) (
Peanut injury as affected by lactofen at Lamesa, Lockett, and Yoakum, TX in 2005 and 2006a.
No injury exceeded 10% following any lactofen treatment in 2005 (
Lactofen injured Tamrun 96 up to 10% following the 6 lf application and up to 20% following other single and sequential applications in 2005 (authors personal observation). In 2006, lactofen applied at 6 lf injured Tamrun OL01 13% 5 days after application (
Early-season lactofen applications (6 lf) caused peanut stunting and foliar injury up to 11%, whereas the 45 DAIT treatment injured peanut 8% when evaluated late August in 2006 (
Peanut injury as affected by lactofen at Ty Ty and Plains, GA in 2006a.
Negligible visual injury was observed at this location over the course of the growing season (
No two-way factorial (initial 6 lf application and the follow-up sequential application) interaction was observed for yield and grade; therefore means within initial application timing pooled over sequential application timings and means within sequential application timing pooled over initial application timings were compared. There was no difference in peanut yield regardless of whether an initial 6-leaf application was made or not (
Peanut yield following lactofen application timings over 9 locations in Texas and Georgia in 2005 and 2006a.
Peanut grade following lactofen application timings over 5 locations in Texas in 2005 and 2006a.
In 9 tests from Georgia and Texas in 2005 and 2006, lactofen caused visible peanut injury at all locations. Mature peanut leaves exposed to lactofen will exhibit bronzing and necrotic lesions, and growth of the next two true leaves may exhibit some cupping and crinkling of leaf margins. Subsequent growth should be normal and plants should quickly outgrow the initial temporary injury conditions. Yield reductions occurred when applications were made at 45 DAIT, which corresponded to beginning to full seed fill. No grade reductions were apparent in any of these studies. Thus, growers who apply lactofen according with manufacturer's label recommendations and prior to seed fill should have confidence that yields will not be negatively impacted despite dramatic above-ground injury symptoms; however, applications made during seed fill may adversely affect yield.
This study was funded in part by the Texas Peanut Producer's Board and the Georgia Commodity Commission for Peanut. We thank Mr. Jarod Steit and Lamesa Cotton Growers (AG-CARES) for their cooperation and field facilities and Lyndell Gilbert, Jim Reed, Kevin Brewer, Dwayne Drozd, Bill Klesel, Charlie Hilton, and Jesse Parker for their technical assistance in this project. We thank Mr. Ben Mullinix for his statistical guidance in the analysis.
Crop Oil Concentrate (85% mineral oil and 15% polyoxyethoxylated polyol fatty acid ester and polyol fatty acid ester), Helena Chemical Company, 225 Schilling Boulevard, Suite 300, Collierville, TN 38017.
Spraying Systems Company, P.O. Box 7900, North Avenue, Wheaton, IL 60188.
SAS software for Windows, Version 9.2. SAS Institute Inc., 100 SAS Campus Drive, Cary, NC 27513.
Contribution of the Department of Plant and Soil Science, College of Agricultural Sciences and Natural Resources, Texas Tech University. Publication No. T-4-607 and approved for publication by the Director of Texas