Materials and Methods

Field trials were conducted in 2007 and 2008 at the University of Georgia Ponder Research Station, near Ty Ty, GA, (Latitude 31.50911; Longitude −83.64813 ) and the Southwest Georgia Branch Experiment Station near Plains, GA (Latitude 32.04675; Longitude −84.37102 ). The soil type at the Ponder Research Station was a Tifton sand with 96% sand, 2% silt, 2% clay, 1.2% organic matter, and pH 6.0. The soil type at the Southwest Experiment Station was a Greenville sandy loam with 71% sand, 13% silt, 16% clay, 1% organic matter, and pH 6.0. Cultivars, planting dates, inverting, and harvest dates are presented in Table 1. Common production practices and Cooperative Extension recommendations were used at all times. Supplemental irrigation was applied as needed.

Table 1.

Peanut varieties, planting dates, application dates, inverting, harvesting dates and May/June rainfall for the pyroxasulfone/peanut tolerance studies in Georgia, 2007–2008.

Herbicide treatments were arranged in a factorial design that included two application timings (PRE or POST) and five pyroxasulfone rates (0, 120, 240, 360, and 480 g ai/ha). All treatments were replicated four times. PRE treatments were activated with irrigation within 48 hours of application. POST treatments of pyroxasulfone were applied between 44 and 51 days after peanut planting and included a non-ionic surfactant (80/20, United Agri Products, Inc., P.O. Box 1286, Greely, CO 80632-1286) at 0.25% v/v. At the time of the POST applications, the peanut plants were in the R1 to R2 stage of growth (Boote 1982 ). Treatments were applied with a CO₂-pressurized backpack sprayer calibrated to deliver 140 L/ha at 220 to 275 kPa. The plot areas were maintained weed-free using a combination of mechanical cultivation, hand-weeding, and commonly used preemergence herbicides (diclosulam, flumioxazin, and pendimethalin).

Visual estimates of crop injury (stunting) were obtained 10 to 15 days after the POST treatments using a scale of 0–100% where 0  =  no injury and 100%  =  complete plant death. At the Ty Ty location only, incidence of tomato spotted wilt virus (TSWV) was measured just prior to peanut inverting by counting the number of disease loci per linear row in 31 cm sections and transforming the data to percentage infection based upon total row length. Peanut yield data were obtained using commercial inverting and harvesting equipment. Peanut yields were adjusted to 10% moisture.

Data were subjected to a mixed model ANOVA with pyroxasulfone rates, application methods and locations as fixed effects and years and interactions as random effects. Where appropriate, data were regressed on pyroxasulfone rate and a sigmoid regression model was fit to the data using SigmaPlot (Version 11, Systat Software Inc., 1735 Technology Drive, Suite 430, San Jose, CA 95110).

Results and Discussion

Crop Injury (stunting)

Peanut stunting at the Ty Ty location did not exceed 5% from any rate or timing of pyroxasulfone (Figure 1). At the Plains location, there was a sigmoidal relationship between peanut stunting and pyroxasulfone rate when applied PRE (p<0.0001). Pyroxasulfone applied PRE at 240 g/ha or less caused less than 5% crop stunting. However, significant crop stunting occurred at 360 g/ha (18% injury) and 480 g/ha (48% injury). This contrast in crop response between locations may be explained due to the differences in soil type, environment, and cultivars. At Plains, soil silt and clay contents were 11 to 14% higher than at Ty Ty. Additionally, combined May + June rainfall totals were greater at the Plains location (Table 1). Crop injury symptoms may be enhanced when residual herbicides are applied to heavier, more adsorptive soils that receive higher rainfall amounts. When compared to AP-3, Georgia Green is considered to be a small-seeded peanut cultivar (Branch 1996; Gorbett 2007). Previous research concluded that smaller-seeded market classes of dry bean were more sensitive to PRE applications of pyroxasulfone than dry beans with larger seeds (Sikkema et al. 2007). In soybean, it has been speculated that plants developing from larger seeds could survive lethal herbicide doses better than plants developing from smaller seeds because they could survive on more cotyledonary food reserves until the herbicide dosage reaches a non-lethal level (Anderson 1970). Additional pyroxasulfone/peanut cultivar tolerance research is needed due to the fact that the cultivars used in these studies have been replaced by larger-seeded, superior disease resistant, and higher yielding cultivars such as Georgia-06G (Branch 2007).

Fig. 1.

The effect of pyroxasulfone rate and application timing on peanut injury (stunting) at two locations in Georgia, 2007–2008. There was a sigmoidal relation between peanut injury and rate of pyroxasulfone when applied PRE at Plains.

Peanut injury from POST applications of pyroxasulfone was less than 10% in these studies. Pyroxasulfone provides no POST weed control activity. However, in other crops, the inclusion of pyroxasulfone in combination with POST herbicides is a strategy to enhance the residual control of susceptible weeds (King et al. 2007; King and Garcia 2008). In peanut, this POST use pattern could be an effective means for controlling weeds with season-long emergence patterns, especially species that are difficult to control with other management tools such as Benghal dayflower and ALS-resistant Palmer amaranth.

Tomato Spotted Wilt Virus (TSWV)

Due to lack of significant interactions, data were combined over years and pyroxasulfone rates. There was a significant effect of pyroxasulfone application timing on the incidence of TSWV. Pyroxasulfone applied PRE resulted in higher incidences of TSWV than POST applications (Table 2). This was unexpected since AP-3 is considered to have excellent resistance to TSWV (Gorbet 2007). In previous research, only POST applications of chlorimuron had an influence on the incidence of TSWV in peanut (Prostko et al. 2009). In other peanut research, applications of diclosulam (PPI), flumioxazin (PRE), imazapic (POST), paraquat (POST), and 2,4-DB (POST) did not affect the incidence of TSWV (Bailey et al. 2000; Faircloth and Prostko 2010; Tubbs et al. 2010; Wilcut et al. 2001). The mechanism of how certain herbicides influence TSWV in peanut has not yet been discovered.

Table 2.

The influence of pyroxasulfone application timing on tomato spotted wilt virus in peanut (‘AP-3’), Ty Ty, Georgia, 2007-2008.^a

Yield

There were no significant effects of pyroxasulfone rates or application timings on peanut yield (Figure 2). In other legume crops, PPI or PRE applications of pyroxasulfone at rates ≥ 209 g ai/ha caused significant yield reductions (Soltani et al. 2008; Sikkema et al. 2007). While there was significant crop injury (stunting) from pyroxasulfone applied PRE at Plains, there was no correlation between this injury and peanut yield for application timing at either location (Figure 3).

Fig. 2.

Influence of pyroxasulfone rate and application timing on peanut yield at two locations in Georgia, 2007–2008.

Fig. 3.

Influence of pyroxasulfone injury (stunting) on peanut yield at two locations in Georgia, 2007–2008.

Summary and Conclusions

These results suggest that pyroxasulfone may have some potential to be utilized in peanut. However, the crop injury (stunting) and TSWV increases associated with the PRE applications of pyroxasulfone are of some concern. Based upon these results and observations from earlier unpublished exploratory trials, peanut tolerance to PRE applications of pyroxasulfone needs further investigation. Additionally, future research on the potential use of pyroxasulfone in peanut should focus on co-applications with POST herbicides such as paraquat or imazapic.

The authors wish to thank Charlie Hilton and Jesse Parker for their technical assistance.

Literature Cited

Anonymous Crop production 2010 summary 2011 National Agricultural Statistics Service: Web-page: http://usda.mannlib.cornell.edu/usda/current/CropProd/CropProd-01-12-2011.pdf. Accessed: January 18, 2011.

Anderson R. N Influence of soybean seed size on response to atrazine Weed Sci. 1970 18 : 162 – 164 .

Bailey W. A Wilcut J. W Spears J. F Isleib T. G and Langston V. B Diclosulam does not influence yield in eight Virginia market-type peanut (Arachis hypogaea) cultivars Weed Technol. 2000 14 : 402 – 405 .

Boote K. J Growth stages of peanut (Arachis hypogaea L.) Peanut Sci. 1982 9 : 35 – 40 .

Branch W. D Registration of ‘Georgia Green’ peanut Crop Sci. 1996 36 : 806 .

Branch W. D Registration of ‘Georgia-06G’ peanut J. Plant Reg. 2007 1 : 120 .

Faircloth W and Prostko E. P Effect of imazapic and 2,4-DB on peanut seed quality, yield, grade, and tomato spotted wilt incidence Peanut Sci. 2010 37 : 78 – 82 .

Geier P. W Stahlman P. W and Frihauf J. C KIH-485 and s-metolachlor efficacy comparisons in conventional and no-tillage corn Weed Technol. 2006 20 : 622 – 626 .

Gorbet D. W Registration of ‘AP-3’ peanut J. Plant Reg. 2007 1 : 126 – 127 .

Grey T. L Prostko E. P Bednarz C. W and Davis J. W Cotton (Gossypium hirsutum) response to simulated imazapic residues Weed Technol. 2005 19 : 1045 – 1049 .

Grichar W. J Lemon R. G Brewer K. D and Minton B. W S-metolachlor compared with metolachlor on yellow nutsedge (Cyperus esculentus) and peanut (Arachis hypogaea) Weed Technol. 2001 15 : 107 – 111 .

Grichar W. J Dotray P. A and Baughman T. A Yellow nutsedge (Cyperus esculentus) control and peanut tolerance to S-metolachlor and diclosulam combinations Weed Technol. 2008 22 : 442 – 447 .

King S. R and Garcia J. O Annual broadleaf control with KIH-485 in glyphosate-resistant furrow-irrigated corn Weed Technol. 2008 22 : 420 – 424.

King S. R Ritter R. L Hagood E. S and Menbere H Control of acetolactate synthase-resistant shattercane (Sorghum bicolor) in field corn with KIH-485 Weed Technol. 2007 21 : 578 – 582.

Knezevic S. Z Datta A Scott J and Porpiglia P. J Dose-response curves of KIH-485 for preemergence weed control in corn Weed Technol. 2009 23 : 34 – 39 .

Moody J. L Maxwell D. J Kunkel J. T and Simmons F. W Weed control and tolerance with KIH-485 in soybean North Cent. Weed Sci. Soc. Res. Report 2005 62 : 151 – 152 .

Porpiglia P. J Nakatani M Ueno R and Yamaji Y KIH-485: a new broad spectrum herbicide (Abstract) Weed Sci. Soc. Am. 2005 45 : 94 – 95 .

Prostko E. P Culpepper A. S Webster T. M and Flanders J. T Tropical spiderwort identification and control in Georgia field crops Tifton, GA Univ. of Georgia Coop. Ext. Circular #884 http://pubs.caes.uga.edu/caespubs/pubs/PDF/C884.pdf 2005 .

Prostko E. P Kemerait R. C Jost P. H Johnson W. C Brown S. N and Webster T. M The influence of cultivar and chlorimuron application timing on spotted wilt disease and peanut yield Peanut Sci. 2009 36 : 92 – 95 .

Prostko E. P and Grey T. L Peanut tolerance to KIH-485 in Georgia Amer. Peanut Res. Educ. Soc. Abstr. 2008 40 : 62 – 63 .

Senseman S. A editor Herbicide Handbook. 9^th ed Champaign, IL Weed Science Society of America 2007 251 – 297 .

Soltani N Nurse R. E Robinson D. E and Sikkema P. H Response of pinto and small red Mexican beans (Phaseolus vulgaris L.) to preplant incorporated herbicides Weed Biology and Management 2008 8 : 25 – 30 .

Sikkema P. H Shropshire C and Soltani N Dry bean response to preemergence-applied KIH-485 Weed Technol. 2007 21 : 230 – 234 .

Steele G. L Porpiglia P. J and Chandler J. M Efficacy of KIH-485 on Texas panicum (Panicum texanum) and selected broadleaf weeds in corn Weed Technol. 2005 19 : 866 – 869 .

Tanetani Y Kaku K Kawai K Fujiioka T and Shimizu T Action mechanism of a novel herbicide, pyroxasulfone Pestic. Biochem. Physiol. 2009 95 : 47 – 55 .

Tubbs J. S Prostko E. P Kemerait R. C Brenneman T. B and Wann D. Q Influence of paraquat on yield and tomato spotted wilt virus for Georgia-02C and Georgia-03L peanut Peanut Sci. 2010 37 : 39 – 43 .

Webster T. M Weed survey – Southern States, Broadleaf crops subsection Proc. South. Weed Sci. Soc. 2009 62 : 509 – 524 .

Wilcut J. W Askew S. D Bailey W. A Spears J. F and Isleib T. G Virginia market-type peanut (Arachis hypogaea) cultivar tolerance and yield response to flumioxazin preemergence Weed Technol. 2001 15 : 137 – 140 .

Young B. G and Young J. M KIH-485 evaluation in soybean North Cent. Weed Sci. Soc. Res. Report 2005 62 : 149 – 150 .