La dinámica de grupos

N.R. Bateman1_{, G.M. Lorenz}2_{, J.T. Hardke}3_{, T.L. Clayton}1_{, N.M. Taillon}2_,

J.K. McPherson2_{, W.A. Plummer}2_{, A.J. Cato}4_{, L.D. McCullars}4_{, J.L. Black}2_,

B.C. Thrash2_{, D.L Frizzel}3_{, G.J. Lee}3_{, and W.J. Plummer}3

Abstract

Studies were conducted to evaluate insecticide seed treatments for control of rice water weevil and evaluate yield benefits across a wide planting window from 2015 to 2017. A reduction in rice water weevil densities was observed for Cruiser® _{and Dermacor}®

X-100 compared to the fungicide only seed treatment, particularly for plantings in mid-May and early-June. A greater increase in yield was observed for earlier plantings compared to later plantings. Cruiser® _{yielded greater than the fungicide only seed treat-}

ment across all planting dates.

Introduction

Approximately 1.1 million acres of rice, Oryza sativa L., are planted annually in Arkansas, making it one of the state’s top commodities (NASS 2017). Due to the large acreage dedicated to rice production, it is planted over a relatively broad 4 month period from late-March through mid-June. Multiple studies have observed yield benefits in rice planted from early to mid-April, compared to May plantings (Hardke et al., 2018).

Rice water weevil, Lissorhoptrus oryzophilus (Kushel), and grape colaspis, Colas-

pis brunnea (F.), are the two most destructive insect pests in Arkansas rice (Lorenz and

Hardke, 2013). Larvae of these pests feed on the roots and underground stem portion of the rice plant (Lorenz and Hardke, 2013). Grape colaspis is a pre-flood pest of rice, with overwintering larvae moving vertically in the soil profile to feed after germination has occurred. Rice water weevil adults are attracted to open water, such as when the

1 _{Assistant Professor/Crop Entomologist and Program Associate I respectively, Department of Entomol-}

ogy, Stuttgart .

2 _{Extension Entomologist, Program Associate, Program Associate, Program Associate, Program Techni-}

cian, and Program Technician respectively, Department of Entomology, Lonoke.

3 _{Rice Extension Agronomist, Program Associate III, Program Associate I, and Program Technician}

respectively, Department of Crop, Soil, and Environmental Sciences, Stuttgart.

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permanent flood is applied to rice fields (Stout et al. 2002). Upon flood establishment, rice water weevil adults migrate into rice fields and begin feeding on the rice foliage. Foliage feeding from adult rice water weevils causes scarring on the leaf surface, but the scarring alone has not been directly associated with yield loss (Tindall and Stout, 2003). Larvae of the rice water weevil prune plant roots and have the potential to cause catastrophic yield loss. (Lorenz and Hardke, 2013). Insecticide seed treatments are the most effective control measures for both of these yield limiting pests (Lorenz and Hardke, 2013).

Procedures

Studies were conducted at the University of Arkansas System Division of Agri- culture’s Rice Research and Extension Center, near Stuttgart Ark., from 2015 through 2017 to evaluate insecticide seed treatments across multiple planting dates. Rice was planted approximately every 15 days from mid-March through early June. The experi- ments were arranged as a split-block within a randomized complete block design. The main plot factor was planting date and the sub-plot factor was seed treatment, with four replications within each planting. For each planting, Roy J was drill-seeded on 7.5 inch spacing at 75 pounds per acre. Four seed treatments were used; Cruiser (Thiamethoxam, Syngenta) at 0.034 mg ai/seed, Nipsit Inside (Clothianidin, Valent) at 0.16 mg ai/seed Dermacor X-100 (Chlorantraniliprole, DuPont) at 0.017 mg ai/seed, and a fungicide only seed treatment. The fungicide only seed treatment consisted of Apron XL (Mefenoxam, Syngenta), Maxim 4 FS (Fludioxonil, Syngenta), and Dynasty 83 FS (Azoxystrobin, Syngenta). The same fungicide package was also applied to the Cruiser, Nipsit Inside, and Dermacor treatments.

Rice water weevil densities were evaluated approximately 21 days after establish- ment of the permanent flood by taking 3 core samples per plot with a 4 inch diameter core sampler. Samples were processed at the University of Arkansas System Division of Agriculture’s Lonoke Agricultural Extension and Research Center, by washing core samples with water into a 40 mesh sieve. Once cores were washed, the sieve was placed into a warm salt water solution allowing the larvae to float and then counted. Yield was recorded using a plot combine equipped with a harvest master system for all plots. An analysis of variance was conducted on all data in SAS 9.4 (Proc GLIMMIX, SAS Institute, Cary N.C.) with an alpha level of 0.05. Due to seed treating issues for Nipsit Inside during 2017, two analysis were conducted. The first analysis consisted of the data from 2015 and 2016 combined for all treatments. The second analysis was all data from 2015 through 2017 excluding Nipsit Inside.

Results and Discussion Rice Water Weevil Efficacy

An interaction between planting date and seed treatment for rice water weevil densities was observed (Fig. 1). In general, greater densities of rice water weevil larvae were observed at later plantings (Fig. 1). The insecticide seed treatments did not differ from the fungicide only until the mid-May planting (Fig. 1). At the mid-May planting

Cruiser and Dermacor X-100 had fewer rice water weevil larvae than the fungicide only, although Nipsit Inside was not different from any of the other treatments (Fig. 1). At the early June planting, all insecticide seed treatments had fewer rice water weevil larvae than the fungicide only, with Dermacor X-100 have fewer rice water weevil larvae than all other treatments (Fig. 1).

A similar interaction between planting date and seed treatment for rice water weevil densities was observed when data was combined for Dermacor X-100, Cruiser, and the fungicide only from 2015-2017. In general, greater densities of rice water weevil larvae were observed at later plantings. Dermacor X-100 and Cruiser had fewer rice water weevil larvae than the fungicide only at the mid-May and early June plantings. Dermacor X-100 and Cruiser only differed from one another at the early-June planting, with Dermacor X-100 having fewer rice water weevil than Cruiser.

Yield

No interaction between planting date and seed treatment was observed for yield for the 2015-2016 data. An effect of planting date was observed for yield (Fig. 2). The mid-March planting yielded greater than all plantings except the mid-April planting (Fig. 2). The early April and mid-May plantings yielded less than all other plantings except the early May planting (Fig. 2). No effect of seed treatment was observed for yield, with all treatments yielding statistically the same.

No interaction between planting date and seed treatment was observed for yield when data was combined for Dermacor X-100, Cruiser, and the fungicide only from 2015-2017. An effect of planting date was observed for yield. Similar to the 2015-2016 data, the mid-March and mid-April plantings had greater yields than all other plantings. The early-June planting had less yield than all plantings except the early-May planting. An effect of seed treatment was also observed for yield (Fig. 3). Cruiser had greater yield than the fungicide only seed treatment (Fig. 3). Dermacor X-100 did not yield different than the fungicide only or Cruiser seed treatments (Fig. 3).

Significance of Findings

Rice planted in May or later is more likely to encounter yield limiting densities of rice water weevil. Insecticide seed treatments can effectively help growers combat these pests. Although Dermacor® _{X-100 had fewer rice water weevils than Cruiser}® _at

the early June planting, overall Cruiser® _{was the only insecticide seed treatment to yield}

greater than the fungicide only seed treatment. An insecticide seed treatment should be considered at all planting dates because there are few effective methods to control rice water weevil larvae once an infestation has occurred.

Acknowledgments

The authors would like to thank to rice producers of Arkansas for funding of this project through check off dollars administered through the Arkansas Rice Research and Promotion Board. Support also provided by the University of Arkansas System Division of Agriculture.

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Fig. 1. Interaction between planting date and seed treatment for rice water weevil larvae densities for studies conducted at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Ark., 2015-2016. Means

with the same letter are not significantly different at α = 0.05.

Literature Cited

Hardke, J.T., R. Baker, T. Barber, N.Bateman, M. Hamilton, C. Henry, G. Lorenz, R. Mazzanti, R. Norman, J. Norsworthy, T. Roberts, B. Scott, N. Slaton, and Y. Wamishe. 2018. 2018 Rice Farming for Profit. University of Arkansas System Di- vision of Agriculture Cooperative Extension Service. Pg. 5. Available at: https:// uaex.edu/farm-ranch/crops-commercial-horticulture/rice/2018%20Rice%20Farm- ing%20for%20Profit.pdf

Lorenz, G. And J. Hardke. 2013. Insect management in rice. In: J.T. Hardke (ed.). Arkansas Rice Production Handbook. University of Arkansas Division of Agricul- ture Cooperative Extension Service. MP192 pp. 139. Available at: https://www. uaex.edu/publications/pdf/MP192 /MP192.pdf

NASS. 2017. United States Department of Agriculture-National Agricultural Statis- tics Service. Cropland Data Layer.

Stout, M.J., M.R. Riggio, L. Zou, R. and Roberts. 2002. Flooding influences ovipo- sitional and feeding behavior of the rice water weevil, Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) J. Econ. Entomol. 95, 715-721.

Tindall, K.V. and M.J. Stout. 2003. Use of common weeds of rice as hosts for the rice water weevil (Coleoptera: Curculionidae). Environ. Entomol. 32, 1227-1233.

Fig. 2. Yield by planting date, across seed treatments, for studies conducted at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Ark., 2015-2016. Means with the same letter are not significantly

different at α = 0.05

Fig. 3. Yield by seed treatment, across planting date, for studies conducted at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Ark., 2015-2017. Means with the same letter are not significantly

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