Using Herbicides in a Peanut Strip-tillage Production System

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W. James Grichar, Texas Agricultural Experiment Station, Texas A&M University, 3507 Hwy 59E, Beeville 78102

Abstract

Field studies were conducted during 2003 and 2004 in the south Texas peanut (Arachis hypogaea) growing region to evaluate herbicides for effective weed control under a strip-tillage production system. Ethalfluralin (Sonalan) plus diclosulam (Strongarm) applied preemergence provided the most consistent control of southern crabgrass, Texas panicum, and yellow nutsedge (> 94%). Ethalfluralin at 2.0 pt/acre plus flumioxazin (Valor) at 3.0 oz/acre applied preemergence controlled southern crabgrass and Texas panicum 75 to 84% while ethalfluralin plus flumioxazin at 2.0 oz/acre controlled those same annual grasses 56 to 76%. Ethalfluralin followed by imazethapyr (Pursuit) or imazapic (Cadre) controlled yellow nutsedge and Texas panicum at least 98% but controlled southern crabgrass only 60 to 78%. Ethalfluralin applied preemergece followed by imazapic or diclosulam applied postemergence provided the highest yields (> 3900 lbs/acre) and net returns.

Introduction

The use of reduced- and strip-tillage systems have reduced production costs in several crops and these systems can result in considerable savings in energy, machinery, and labor requirements (6). Soil erosion, declining soil productivity, and surface water quality have become major concerns in recent years and have created much interest in conservation tillage (15).

Poor weed control, especially annual grasses, has been one of the major problems in reduced-tillage cropping systems (6). With the use of reduced-tillage systems, shifts toward perennial weeds such as horsenettle (Solanum carolinense L.), bermudagrass [Cynodon dactylon (L.) Pers.], and yellow nutsedge (Cyperus esculentus L.) have been reported (9,13).

Peanut producers generally have not adopted reduced-tillage production systems because poor weed control has resulted in reduced yields in some areas, and also, because of the success achieved with weed management systems in conventional peanut production (6). Also, the limited use of reduced-tillage systems may be due to a perceived need for burial of crop residues to reduce the possibility of disease problems (10).

Reduced-tillage systems require more intensive management to maintain adequate season-long weed control than do conventional peanut production systems (6). Peanut is a poor competitor early in the growing season and generally requires six to eight week weed-free period to achieve maximum yields (3). There has been limited information published on weed management systems for peanut under reduced-tillage systems compared with other agronomic crops (4,6,17).

Considering the growing awareness of environmental issues, more research is needed to develop effective and economical weed management programs for peanut in reduced-tillage systems. Therefore, the objectives of this research were to: (i) identify herbicide systems which provide acceptable weed control under a strip-tillage system, (ii) evaluate peanut yields in a strip-tillage system, and (iii) determine the most economical herbicide system for a strip-tillage production system.

Field Experiments with Several Herbicide Systems

Field studies were conducted during the 2003 and 2004 growing season on a producers farm near Pleasanton, TX. Soil at this location was a Wilco loamy fine sand (fine, mixed, hyperthermic Udic Paleustalfs) with 1% organic matter. This study site was watered with supplemental irrigation. The experimental design was a randomized complete block with four replications. Plots consisted of two rows, 25 feet long, and spaced on 38-inch centers. All field plots had naturally moderate to high populations of Texas panicum (Panicum texanum Buckl.) (2 to 4 plants per ft²), southern crabgrass (Digitaria ciliaris L.) (1 to 3 plants per ft²), and yellow nutsedge (4 to 8 plants per ft²).

The experimental area in each year was seeded with wheat (Triticum aestivum L.) in the fall previous to the spring peanut planting. The small grain was shredded to approximately a 12-inch height after harvesting, approximately 3 weeks prior to peanut planting. Glyphosate (1 qt/acre) was applied 10 to 14 days prior to the strip-tillage operation to kill the small grain cover crop and any existing weeds.

Seedbeds were prepared with a Bush-Hog Ro-Till (Bush-Hog, Inc., Selma, AL) unit which tilled a 14- to 16-inch-wide planting strip on 38-inch centers. The Ro-Till unit consists of a sub-soil shank which penetrates the soil to a depth of approximately 16 inches. Twin sets of fluted coulters were mounted on either side of these shanks. The sub-soiler shank opens the soil and destroys any plow-pan beneath the row. The fluted coulters smooth the soil and break any large clods. Rolling crumblers mounted immediately behind the fluted coulters further smooth and shape the seedbed.

Tamrun 96 and OL-01 peanut seed were planted at the rate of 90 lb/acre on June 17, 2003 and June 12, 2004, respectively. Ethalfluralin was selected as the dinitroaniline herbicide of choice because approximately 30% of the peanut growers in the southwest U.S. are using it in their peanut herbicide program (W. J. Grichar, personal observation). The use rates for all herbicide treatments are shown in Table 1.

Table 1. Weed control, peanut yield, and net returns with various herbicides under a strip-tillage system.

Postemergence applications of diclosulam, imazethapyr, and imazapic included Agridex (Valent USA Corp., Walnut Creek, CA) at 1.0 qt/acre. Preemergence herbicides were applied immediately after planting, whereas postemergence herbicides were applied when annual grasses were 15 to 20 cm high. Yellow nutsedge was approximately 20 to 25 cm tall at time of herbicide application. Herbicides were applied with a compressed air bicycle sprayer using Teejet 11002 flat fan nozzles (Spraying Systems Co., Wheaton, IL) which delivered a spray volume of 20 gal/acre. Nozzles were spaced 18 inches apart, with one nozzle over each row and another in the middle between the two rows, to deliver a uniform broadcast spray over the 2 rows.

Weed control was visually rated on the basis of weed density on a scale of 0 to 100 where 0 = no control and 100 = complete control, relative to the untreated check. Yields were determined by digging peanut plants, air-drying in the field for 4 to 6 days, and harvesting individual plots with a combine. Herbicide costs were calculated as a result of a phone conversation with an agricultural chemical distributor (B. Carr, Helena Chemical Co., Pearsall, TX). Application costs were calculated at $3.32/acre (L. Falconer, Texas Agricultural Experiment Station, Corpus Christi, TX). Value of peanuts was calculated at a base support price of $366.08/ton (16). Peanut grade (Sound mature kernels + sound splits) was calculated based on a grade of 75 with no deductions for foreign material, damaged kernels, sound splits, or other kernels based on peanut loan schedule (16). Ratings, yields, and net returns per acre were subjected to analysis of variance. Weed ratings were subjected to arcsin transformations for analysis and means were determined. Statistical results did not differ from the non-transformed data; therefore, non-transformed data are presented. Means were separated with Fisher’s Protected LSD at the 5% level. Analysis of variance revealed no significant treatment by location interaction for any variable tested; therefore, results are combined over years.

Effect of Herbicides on Weed Control, Peanut Yield, and Net Returns

Forty year average rainfall amounts for June, July, August, September, and October for the area are 3.8, 1.8, 2.5, 3.6, and 3.0 inches, respectively (B. Easterling, personal communication). In 2003, rainfall was below normal for June (less than 3.0 inches) but above normal for July (8.2 inches). Two irrigations (1.5 inches each) were applied in August due to less than 1.0 inch of rainfall. No irrigation was applied in September or October due to 9.25 and 2.2 inches of rainfall for those two months, respectively. In 2004, 8.25 inches of rainfall was received in June while two irrigations (1.5 inches each) were applied in July when only 0.75 inch of rainfall was received. August, September, and October received 4.1, 1.8, and 3.0 inches of rainfall, respectively; therefore no irrigation was applied during those months.

Weed control. Yellow nutsedge control was at least 98% when ethalfluralin was applied in combination with diclosulam applied preemergence or followed by diclosulam, imazethapyr, or imazapic applied postemergence (Table 1). Yellow nutsedge control can vary with diclosulam rate and method of application (1,8,18). Wilcut et al. (18) also determined that soil applications of diclosulam resulted in reduced shoot dry weights of yellow nutsedge and purple nutsedge (Cyperus rotundus). Grey et al. (5) reported that increasing the rate of diclosulam applied preplant incorporated from 9 to 52 g/ha increased yellow nutsedge control but additional postemergence herbicides were needed for acceptable control.

Ethalfluralin in combination with metolachlor applied preemergence controlled 74% yellow nutsedge while ethalfluralin in combination with dimethenamid applied preemergence controlled 47%. Several herbicides are registered for use in peanuts for nutsedge control. However, control can be extremely variable when conditions at application are less than ideal (7,18). Reasons for failure include marginal translocation of herbicides to sites of action, temporary inhibition of tuber sprouting, or inconsistent control when applied at different stages of growth and under various environmental conditions (7,18). The use of metolachlor can delay tuber sprouting and kill yellow nutsedge (7). Grichar et al. (7) reported that metolachlor controlled yellow nutsedge better than dimethenamid when applied at 0.6× to 2× the suggested label rates. They attributed the lack of season-long yellow nutsedge control with dimethenamid to poor soil persistence. Mueller et al. (11) reported that soil concentrations of metolachlor were higher later in the season compared to dimethenamid and therefore, metolachlor provided consistent control of annual grasses longer into the growing season.

Southern crabgrass control was best with ethalfluralin plus diclosulam applied preemergence (95%) while only ethalfluralin plus flumioxazin at 3.0 oz/acre applied preemergence or ethalfluralin followed by imazapic applied postemergence controlled at least 75% (Table 1). Ethalfluralin plus flumioxazin at 2.0 oz/acre controlled only 56% southern crabgrass. The dinitroaniline herbicides can be applied preemergence but they must be incorporated for effective control (12). Initial studies in peanut indicated that ethalfluralin provided 85 to 100% control of goosegrass [Eleusine indica (L.) Gaertn.], southern crabgrass, and Florida pusley (Richardia scabra L.) when applied preemergence (2). However, later research showed that preemergence applications of ethalfluralin or pendimethalin (Prowl) were not effective for weed management in peanut (6,17). Prostko et al. (12) reported that applications of ethalfluralin or pendimethalin followed by irrigation were as effective as preplant incorporated applications in controlling Texas panicum, southern crabgrass, and crowfootgrass [Dactyloctenium aegyptium (L.) Willd.]. The effectiveness of soil-applied herbicides is dependent on several factors, including movement of the herbicide into the soil either through rainfall or irrigation or by mechanical incorporation (14).

Texas panicum control was greater than 90% with ethalfluralin plus diclosulam applied preemergence or ethalfluralin followed by diclosulam, imazethapyr, or imazapic applied postemergence (Table 1). Ethalfluralin plus flumioxazin at 3.0 oz/acre applied preemergence controlled 84% Texas panicum while ethalfluralin plus flumioxazin at 2.0 oz/acre applied preemergence controlled 76%. Ethalfluralin alone or in combination with metolachlor or dimethenamid controlled no greater than 67% Texas panicum. The dinitroaniline herbicides are the only soil-applied herbicides registered for use in peanut that will provide full-season control of Texas panicum (18). Grichar et al. (6) reported that pendimethalin alone failed to adequately control Texas panicum but the addition of metolachlor improved control up to 15%. Wilcut et al. (18) reported that pendimethalin applied preemergence controlled no greater than 65% Texas panicum compared with at least 90% control for preplant incorporated applications. They attributed this lack of control to the ability of the larger seed of Texas panicum to germinate from greater soil depths.

Peanut yield. Ethalfluralin followed by diclosulam or imazapic applied postemergence provided the highest yield (Table 1). However, no herbicide treatment produced yields better than the check (statistically). Ethalfluralin plus flumioxazin applied preemergence produced peanut yields that were no different from ethalfluralin alone, ethalfluralin plus metolachlor or ethalfluralin plus dimethenamid. This yield reduction may be due to poor annual grass and no yellow nutsedge control. Herbicide systems which controlled Texas panicum better than 80% provided yields of at least 3300 lbs/acre. Competition between annual grasses and peanut not only reduces yield, but can also reduce harvesting efficiency because peanut pods become embedded in the annual grasses root system and stripped from the vine during digging (3,7,8).

Effective control of yellow nutsedge and annual grasses is possible under a reduced-tillage system in peanut with several herbicides. Ethalfluralin plus diclosulam applied preemergence or ethalfluralin applied preemergence followed by imazapic applied postemergence provided the most consistent weed control and among the highest yields. However, weed escapes do occur, and this will frequently require the use of a postemergence grass herbicide. In the southeast U.S. peanut production region, paraquat has effectively controlled Texas panicum early in the growing season (18); however, because paraquat is seldom used in the southwest (W. J. Grichar, personal observation), clethodim (Select) or sethoxydim (Poast) will likely be needed to control grass escapes.

Net returns. Herbicide costs were over $30/acre with the ethalfluralin plus dimethenamid system while ethalfluralin alone, ethalfluralin plus flumioxazin at 2.0 oz/acre, or ethalfluralin followed by diclosulam were less than $20/acre (Table 1). Net returns closely followed trends in yield. Herbicide systems which included ethalfluralin applied preemergence followed by diclosulam or imazapic applied postemergence provided the highest net returns while ethalfluralin plus metolachlor or flumioxazin at 2.0 oz/acre provided net returns of less than $550/acre.

Acknowledgments

The National Peanut Board as administered by the Texas Peanut Producers Board provided funds for this research. Kevin Brewer, Dwayne Drozd, and Bill Klesel helped in plot maintenance and peanut harvest.

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