W. James Grichar

Purple Nutsedge Control and Potato (Solanum tuberosum) Tolerance to Sulfentrazone and Halosulfuron1

Five field studies on sandy soils with ≤ 1% organic matter in south Texas showed that halosulfuron at 0.066 kg/ha preemergence (PRE) controlled ≥ 92% purple nutsedge and at 0.066 kg/ha postemergence (POST) controlled purple nutsedge 77 to 95%. Sulfentrazone at 0.11 to 0.28 kg/ha PRE or POST controlled purple nutsedge < 65% at one location but > 75% at two other locations. Poor control at the one location may have been due to a lack of early-season rainfall or irrigation. Potatoes were stunted 5 to 26% with halosulfuron PRE, whereas POST treatments caused 7 to 40% stunting. Sulfentrazone at 0.11 to 0.28 kg/ha applied PRE or POST caused 2 to 38% stunting. ‘Atlantic’ potato stunting with sulfentrazone POST at 0.14 to 0.28 kg/ha was ≥ 20%, whereas ‘Snowden’ and ‘1625’ potatoes were stunted ≤ 20%. Potato yields were reduced 65 and 39% with sulfentrazone and halosulfuron POST, respectively, at the high rates, but yield reductions occurred with all POST treatments on Atlantic potatoes 10- to 20-cm tall. Halosulfuron PRE at 0.033 kg/ha and sulfentrazone PRE at 0.14 kg/ha did not reduce yields; however, all other treatments of halosulfuron and sulfentrazone reduced potato yields. Nomenclature: Halosulfuron; sulfentrazone; purple nutsedge, Cyperus rotundus L. #3 CYPRO; potato, Solanum tubersum L., ‘Atlantic’, ‘Snowden’, ‘1625’. Additional index words: Preemergence, postemergence. Abbreviations: OM, organic matter; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting.

Horse Purslane (Trianthema Portulacastrum), Smellmelon (Cucumis Melo), and Palmer Amaranth (Amaranthus Palmeri) Control in Peanut with Postemergence Herbicides

Field studies were conducted during the 2003 through 2005 growing seasons to evaluate postemergence herbicides and timing of application for horse purslane, smellmelon, and Palmer amaranth control in peanut. Acifluorfen provided inconsistent control of the three weed species. Bentazon failed to control Palmer amaranth, horse purslane, and smellmelon (< 65%), whereas 2,4-DB controlled horse purslane and smellmelon less than 70%. Diclosulam applied early postemergence (EPOST) controlled Palmer amaranth at least 77% but horse purslane control varied from 27 to 73% when applied EPOST and was less than 50% with the late postemergence (LPOST) application. Diclosulam controlled smellmelon less than 65%. Imazethapyr and imazapic controlled Palmer amaranth and smellmelon at least 70% but controlled horse purslane less than 65%. Lactofen controlled Palmer amaranth and horse purslane at least 93% with the EPOST application but had inconsistent control (40 to 100%) when applied LPOST. Smellmelon control with lactofen was also inconsistent. Removal of weed interference with all herbicides except bentazon provided peanut yields greater than the nontreated check. Nomenclature: Acifluorfen, bentazon, diclosulam, imazapic, imazethapyr, lactofen, 2,4-DB, horse purslane, Trianthema portulacastrum L. TRTPO, Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, smellmelon, Cucumis melo L. var. Dudaim Naud. CUMME, peanut, Arachis hypogaea L. ‘Tamrun 96.’

S-Metolachlor Compared with Metolachlor on Yellow Nutsedge (Cyperus esculentus) and Peanut (Arachis hypogaea) 1

Abstract: S-metolachlor was compared with metolachlor at four field locations in Texas during the 1996 and 1997 growing seasons in terms of yellow nutsedge control, peanut injury, and peanut yield. S-metolachlor caused peanut injury comparable to metolachlor when either herbicide was applied preplant incorporated or preemergence. Yellow nutsedge control was similar and peanut yields were comparable with the two herbicides. At one location where yellow nutsedge failed to develop, the untreated check produced one of the highest yields. Nomenclature: Metolachlor; S-metolachlor; yellow nutsedge, Cyperus esculentus L. #3 CYPES; peanut, Arachis hypogaea L. ‘Florunner’, ‘AT-120’, ‘GK-7’. Additional index words: Groundnut, herbicide efficacy, peanut stunting. Abbreviations: POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Effect of Imazapic Application Timing on Texas Peanut (Arachis hypogaea)1

Abstract: Field experiments conducted in Texas at six locations from 1996 to 1998 evaluated peanut tolerance to imazapic applied postemergence. Imazapic at 71 g ai/ha was applied weekly from ground cracking to 56 d after ground cracking (DAGC). Visible injury 70 DAGC ranged from 0 to 40%. No reduction in canopy height, canopy width, yield, or grade was observed at harvest following any imazapic treatment. Nomenclature: Imazapic; peanut, Arachis hypogaea L., ‘AT 120’, ‘GK 7’, ‘NC 7’, ‘Tamspan 90’. Additional index words: Herbicide injury, ground cracking, groundnut, herbicide timings, peanut injury, postemergence, yield. Abbreviations: DAGC, days after ground cracking; DAP, days after planting; POST, postemergence; PPI, preplant incorporated.

The Persistence of Imazapic in Peanut (Arachis hypogaea) Crop Rotations1

Field studies were conducted at Yoakum and Stephenville, TX; Jay, FL; and Midville and Plains, GA, to determine the persistence of imazapic applied to peanuts at 0, 70, 140, and 210 g ai/ha. The following year, cotton, sorghum, and corn were planted in the treated plots in Texas, cotton was planted in Florida, and corn and cotton were planted in Georgia and evaluated for carryover injury. Data collected to determine injury included plant heights and weights. In 1999 in Texas and in Florida and Georgia, there was no significant carryover injury to rotational crops from any of the imazapic rates. Data on cotton and sorghum plant height from Texas in 2000 showed height reductions for the 210-g/ha rate on cotton and the 140- and 210-g/ha rates on sorghum. These data showed no significant carryover effects to rotational crops from the 70-g/ha rate of imazapic applied to peanuts the previous year. Nomenclature: Imazapic; cotton, Gossypium hirsutum L.; corn, Zea mays L.; peanut, Arachis hypogaea L.; sorghum, Sorghum bicolor L. Additional index words: Carryover injury, herbicide persistence, herbicide residue. Abbreviations: DAP, days after planting; EPOST, early postemergence; MAP, months after planting; PPI, preplant incorporated.

Herbicide Systems for Control of Horse Purslane (Trianthema portulacastrum L.), Smellmelon (Cucumis melo L.), and Palmer Amaranth (Amaranthus palmeri S. Wats) in Peanut

Abstract Field studies were conducted during the 2003 through 2005 growing seasons to evaluate soil-applied herbicides alone or in combination with postemergence (POST) herbicides for horse purslan...

Citronmelon (Citrullus lanatus var. citroides) Control in Texas Peanut (Arachis hypogaea) Using Postemergence Herbicides1

Abstract: Field studies were conducted from 1995 through 1998 to evaluate citronmelon control with postemergence (POST) herbicides. Imazapic at any application timing and late postemergence (LPOST) applications of 2,4-DB were the only herbicides that provided >80% control of citronmelon late season. Other herbicides such as acifluorfen, imazethapyr, lactofen, and pyridate provided acceptable (>75%) early-season control of citronmelon, but control was inadequate at harvest. Nomenclature: Acifluorfen; imazapic; imazethapyr; lactofen; pyridate; 2,4-DB; citronmelon, Citrullus lanatus var. citroidas #3 CITCL; peanut, Arachis hypogaea L. ‘GK-7’. Additional index word: Groundnut. Abbreviations: DAP, days after planting; EPOST, early postemergence; LPOST, late postemergence; POST, postemergence.

Row Spacing, Plant Populations, and Cultivar Effects on Soybean Production Along the Texas Gulf Coast

Three soybean (Glycine max L.) cultivars were compared when planted in twin rows (two rows spaced 4 to 6 inches apart on a single bed with 38-inch centers) to soybean produced in single rows on a bed (spaced 38 inches apart) at three seeding rates of 6, 10, and 15 seeds/planted ft at two locations along the Texas Gulf Coast in 2003 and 2004. Soybean yield averaged over cultivars and seeding rates resulted in the twin-row system out-producing the single-row system at two of the four site-years. Soybean yield did not increase as the seeding rate increased with either row spacing. When only seed costs were considered, the twin-row system planted at 6 seeds/ft had the highest net return at three of the four site-years. Introduction Soybean producers are continually searching for methods that will help increase yields, reduce costs, or a combination of the two. The use of twin-row systems have resulted in yield increases over a single row system in several crops including corn (Zea mays L.), cotton (Gossypium hirsutum L.), and peanut (Arachis hypogaea L.) (1,5,10,12,15). Several studies have demonstrated the benefit of decreased row spacing on early season canopy development (6,7,11,17,18). In peanuts, Jaaffar and Gardner (13) reported that narrow and twin-row patterns had greater ground cover, leaf area indices, canopy light interception, crop growth rates, and ultimately higher pod yields when compared to a conventional row pattern. Seedlings in close proximity to each other express phytochrome-mediated responses by developing narrow leaves, long stems, and less massive roots (14). Planting a crop in a pattern that reduces the spacing of plants within and between rows can increase plant biomass and leaf area index (3). Work in the late 1980s showed that reduced row spacing increased the total interception of photosynthetic active radiation by the corn canopy and redistributed the radiation toward the top of the canopy (16). Reduced row spacing are also thought to increase weed control by increasing the competitiveness of a crop with weeds and by reducing light transmission to the soil surface (19). Teasdale (19) showed that reduced row spacing and increased corn populations decreased weed growth in the absence of herbicides and shortened the time of canopy closure by one week. Twin-row systems have been compared in soybean (Glycine max L.) with mixed results. Graterol et al. (9) reported that soybean planted in the twin-row system had no yield advantage over the conventional single-row system in a year with yield-limiting conditions. However, in a year with no yield-limiting conditions, the twin-row planting systems offered yield advantages over a singlerow planting system. Other studies have reported on the use of narrow row spacing in soybean. Maturity group V to VII determinate soybean grown in narrow rows (generally 50 cm or less) produced higher yield than soybean grown in wide row spacing in the southern US (4,8,20). 15 June 2007 Crop Management Little use of twin-row soybean production has occurred along the Texas Gulf Coast soybean production area. This study was designed to increase the knowledge about twin-row soybean production for this area. The two objectives were: (i) evaluate a mid-group-IV soybean cultivar and an early group V cultivar produced in twin-rows compared to conventional 38-inch rows, and (ii) compare both row spacings when planted at the rate of 6, 10, and 15 seeds per planted foot. Field Procedures Soybean was planted near El Campo and Pt. Lavaca, TX on 24 March 2003 and on 29 March, 2004 near Pt. Lavaca and 21 April 2004 near El Campo. Different planting dates in 2004 occurred due to wet conditions at the El Campo location during the latter part of March. The experimental design for each year was a factorial arrangement using a randomized complete block with three replications at each location. Factors were row spacing (2), seeding rates (3), and soybean cultivars (2). Soybean cultivars used in 2003 at both locations were HBK 5101 and DP 4446 while in 2004 the cultivars at El Campo were HBK 5123 and Pioneer 94M90 and the cultivars at Pt. Lavaca were HBK 5101 and DP 4724. Boundary (S-metolachlor plus metribuzin) was applied preemergence at 1.0 qt/acre for weed control. Select (clethodim) was used postemergence at 10 oz/acre to control any annual grass escapes while Blazer (acifluorfen) was used at 1.5 pt/acre to control any broadleaf weed escapes. Weeds were treated when less than 6 inches tall and all postemergence herbicide treatments included Agridex added at the rate of 0.25% v/v. Each twin-row plot had two sets of twin rows (two rows spaced 4 to 6 inches apart on a single bed spaced on 38-inch centers) that were planted with a Monosem vacuum planter (Monosem ATI Inc., Leneka, KS) equipped with precision seed meters. Conventional planted soybeans were planted in the middle of the raised bed also spaced on 38-inch centers. Two trips were made through each plot to plant the twin-rows since planters were off-set from the row center while conventionally planted soybeans were centered directly over the row. Plots were planted at a rate of 6 (82,700 seeds/acre), 10 (137,400 seeds/acre), and 15 (206,100 seeds/acre) seed per planted foot; therefore the twin-row actually had 12 (165,400 seeds/acre), 20 (274,800 seeds/acre), and 30 (412,200 seeds/acre) seed planted per linear foot. Seedling emergence counts were taken approximately six weeks after planting. Pod height measurements (mean difference from the ground to the first node on the main stem with the pod attached) were taken in 2003 but not 2004. Lowest pod were measured prior to harvest. Five plants per plot were measured and an average recorded. Harvesting was accomplished mechanically with a small plot combine and plot yields adjusted to 13% moisture. Net returns were based on seed costs only and did not include land preparation, herbicide, or insecticide costs. Seed costs were calculated based on calls to local seed representatives. Seed costs were based on a cost of

Weed Control and Grain Sorghum (Sorghum bicolor) Response to Postemergence Applications of Atrazine, Pendimethalin, and Trifluralin'

35.00 per bag at 150,000 seeds per bag count while the soybean price was calculated at

Field Sandbur (Cenchrus spinifex) Control and Bermudagrass Response to Nicosulfuron Tank Mix Combinations

5.88/bu based on the close of the market on 21 February, 2006. Data were analyzed using PROC GLM with SAS (SAS Institute, Inc., Cary, NC) and a model statement appropriate for a factorial design. Treatments means were separated by Fisher’s protected least significant difference test at P = 0.05. Data for the two years were analyzed separately due to changes in soybean varieties. Yearly Rainfall In 2003 at El Campo, below average rainfall was received for March through May with average to above average rainfall for June through July, while in 2004 rainfall was above average for all months except March and July (Table 1). At Pt. Lavaca, in 2003, very little rainfall was received in April, May, and August with below average rainfall for June and July. In 2004, only April resulted in above average rainfall while the other months were extremely dry (Table 1). 15 June 2007 Crop Management Table 1. Rainfall amounts at the two locations in 2003 and 2004. Plant Populations Row spacing interacted with seeding rate for each year at both locations. Plant populations increased when seeding rates were increased from six to ten seeds/ft but a decrease in plant populations was noted when the seeding rate was increased from ten to fifteen seeds/ft at both the twin and 38-inch row spacings (Table 2). Other research has shown that optimal plant populations vary from 12,000 to 202,000 plants per acre (4,8). The optimal soybean plant population can vary by as much as 100% across years, even when the same cultivar is grown in the same location (20). This variability can be explained by environmental conditions, with the optimal plant populations increasing under adverse conditions (20). Table 2. Soybean plant populations (plants/planted foot) as influenced by row spacing and seeding rates in 2003 and 2004 at El Campo and Pt. Lavaca. Row Spacing Effects on Pod Height. Lowest pod height was significantly higher in twin rows than single rows for HBK 5101 and DP 4446 at El Campo in 2003 while at the Pt. Lavaca location no response was seen to the twin-row effect with either variety (Table 3). No response to pod height was seen with seeding rate (data not shown). Bowers et al. (2) reported that soybean plant and pod heights were generally greater in the twin rows than in the single row planting system; however, in general, row spacing had no measurable effect on pod height. Month Rainfall amounts (inches)