The weed Phalaris brachystachys Link (short-spiked canarygrass) severely affects cereal production in regions with a Mediterranean climate. A mathematical model for simulating the population dynamics of this weed was constructed using previously reported brachystachys populations

Bastida Milián, Fernando

González Andújar, José Luis

González Díaz, L.

English

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Instituto Nacional de Investigación y Tecnología Agraria y Alimentación (INIA) Spanish Journal of Agricultural Research 2009 7(1), 155-159Available online at www.inia.es/sjar ISSN: 1695-971-XShort communication. Modelling of the population dynamics of Phalaris brachystachys Link under various herbicide control scenariosin a Mediterranean climateL. González-Diaz1, F. Bastida2 and J. L. Gonzalez-Andujar1*1 Crop Protection Department. Instituto de Agricultura Sostenible (CSIC). Apdo. 4084. 14080 Córdoba. Spain.2 Departamento de Ciencias Agroforestales, Universidad de Huelva, Huelva, Spain.AbstractThe weed Phalaris brachystachys Link (short-spiked canarygrass) severely affects cereal production in regions with aMediterranean climate. A mathematical model for simulating the population dynamics of this weed was constructed usingpreviously reported data and new information. The model was used to describe the long-term dynamics of the populationin the absence of control practices and to predict the effect of various control strategies based on the annual application ofherbicides at 50%, 75% and 100% of the standard rate in winter wheat. Without control the seed bank population wouldreach an equilibrium level at a density of 21,244 seeds m-2 after six years. Annual application of herbicides at 50%, 75%and 100% of the standard rate resulted in reductions in the equilibrium position of the population of only 5.44%, 12.27%and 26.14%, respectively. Sensitivity analysis indicated that seedbank dynamics was particularly sensitive to fecundity,seed bank mortality and seed losses, and that new control strategies should target these population parameters. The currentmodel has highlighted the fact that herbicide tactics are not able to stabilize or decrease short-spiked canarygrass popula-tions in winter wheat in the longer-term. Integration of herbicide applications and agronomic practices may be required toattain effective reductions of P. brachystachys populations.Additional key words: density-dependence, population model, seed bank, sensitivity analysis, short-spiked canary-grass, simulation, winter wheat.ResumenComunicación corta. Modelización de la dinámica de poblaciones de Phalaris brachystachys bajo diversos escena-rios de control herbicida en un clima mediterráneoPhalaris brachystachys Link (alpiste) es una mala hierba que afecta de forma importante a la producción de cereales enregiones de clima mediterráneo. En este trabajo se desarrolló un modelo matemático para simular la dinámica de pobla-ciones de esta especie. El modelo fue utilizado para describir el comportamiento a largo plazo de las poblaciones en ausen-cia de prácticas de control y para predecir el efecto de varias estrategias de control basadas en la aplicación de herbicidasal 50%, 75% y 100% de la dosis recomendada en trigo de invierno. En ausencia de control el banco de semilla alcanzó unnivel de equilibrio a una densidad de 21.244 semillas m-2 al sexto año. Bajo aplicación anual de herbicidas al 50%, 75% y100% de la dosis comercial, la posición de equilibrio de la población se redujo en sólo 5,44%, 12,27% y 23,14% respec-tivamente. El análisis de sensibilidad indicó que el modelo fue particularmente sensible a la fecundidad, mortalidad delbanco de semilla y pérdida de semillas, por tanto, las nuevas estrategias de control deberían estar dirigidas en esta direc-ción. El modelo desarrollado muestra la dificultad de estabilizar o disminuir la población de alpiste a largo plazo en trigode invierno. Con el objetivo de obtener un reducción efectiva de las poblaciones de P. brachystachys se requiere una inte-gración de control por herbicidas con practicas culturales.Palabras clave adicionales: alpiste, análisis de sensibilidad, banco de semillas, dependencia de la densidad, modelo depoblación simulación, trigo de invierno.Abbreviations used: RMS (residual mean square), SI (sensitivity index).* Corresponding author: andujar@cica.esReceived: 25-03-08. Accepted: 16-10-08.Phalaris brachystachys Link (Short-spiked canary-grass) is an annual grass considered among the mosttroublesome weeds of cereals in Mediterranean climates(Catizione and Viggiani, 1980; Bell, 1992; Jimenez-Hidalgo et al., 1997). In Spain, it is particularly abun-dant in the southern part of the country, where it repre-sents a major problem in winter cereals (Gonzalez-Andujar and Saavedra, 2003). Yield losses caused bythis weed may be very large (Catizione and Viggiani,1980; Godinho and Costa, 1981; Jimenez-Hidalgo,1993). For instance, P. brachystachys has been reportedto decrease wheat yield by 16% to 60% (Cudney andHill, 1979; Jimenez-Hidalgo et al., 1997; Afentouli andEleftherohorinos, 1999). In Spain the method of controlling this weed is basedmainly on the use of herbicides. Since herbicides regis-tered for P. brachystachys are relatively expensive,reducing herbicide application rates is becomingincreasingly common practice in Spain. However, it isnot clear what effect this practice will have on the long-term control of this weed.The few studies on P. brachystachys biology andmanagement in mediterranean climates (Jimenez-Hidalgo, 1993; Gonzalez-Andujar et al., 2005) areinsufficient to provide insights into the long-termeffects of control strategies. Population models, basedon experimental data on the annual life-cycle of weeds,have been used to investigate the long-term effects ofusing different management strategies (Gonzalez-Andu-jar and Fernandez-Quintanilla, 1993; Holst et al., 2007).The aim of this study is to describe a mathematicalmodel for short-spiked canarygrass and use it to explorea variety of tactical control scenarios. The model is alsoused to identify gaps in knowledge of P. brachystachyslife-cycle, through a sensitivity analysis, that may serveas foci for future investigations.The model structure used was a life cycle-basedmodel similar to the originally proposed by Sagar andMortimer (1976). Such models have been modified andused by many others authors (Doyle, 1991; Holst et al.,2007), including in the management of weeds in Span-ish cereal cropping systems (Gonzalez-Andujar andFernandez-Quintanilla, 1991, 2004; Torras et al., 2008).In our model, weed seed in the seedbank at the timet is indicated as St. Each year a fraction, m, of seedsexperience natural mortality, and a fraction, g, emerge.The density of plants that emerge and survive until theadult stage is indicated as Pt. A fraction, s, survives untilreproduction. Each surviving plant will produce onaverage f viable seeds representing the seed rain thatreturns to the seed bank. A fraction, p, of the total seedrain is assumed to be losses by biotic and abiotic factors.The dynamics is then described by,St+1=(1-g) (1-m)St+sf (1-p)Pt [1]The effect of weed plant density on fecundity (densi-ty-dependence factor) f is introduced by, f=f0 /(1 + aPt ) [2]where f0 is the number of seeds produced by an isolatedplant, a is the area required by a plant to produce f0seeds (Gonzalez-Andujar and Fernandez-Quintanilla,1991). A fraction c of emerged plants is killed by weed con-trol. The density of seedlings that survive weed control isPt=(1-c)gSt [3]Parameter values used in the model were obtainedfrom the literature (Jimenez-Hidalgo, 1993; Gonzalez-Andujar et al., 2005) (Table 1). The relationshipbetween fecundity and plant density [Eq. 2] was fittedto a data set from Jimenez-Hidalgo (1993) by non-linearleast-squares assuming a normal error distribution; thegoodness of fit was judged by residual mean square(RMS), estimation of parameters, R2, and visual exami-nation of the residuals (R2=0.90; RMS=1032,04, df=16).The parameter values obtained were f0=1454 anda=0.06. For simulation purposes an initial seed bank popula-tion of 100 seeds m-2 was considered. The model wasrun over 15 years. This time-span was considered to belong enough to evaluate long-term trends in P. brachys-tachys population dynamics in relation to herbicide use. In the model described here all the parameters areassumed to be constant, but in practice most of theseparameters vary from year to year because of the highvariability in abiotic environment, like locality andweather conditions.A sensitivity analysis was done in order to asses thesensitivity of the model to the variation of the demogra-phy parameters described. A sensitivity index (SI) wascalculated (Pannell, 1997):SI= | (Dmax-Dmin)/D | [4]Where Dmax is the model output result when theparameter in question is set at its maximum value156 L. Gonzalez Diaz et al. / Span J Agric Res (2009) 7(1), 155-159(Pmax), Dmin is the output result for the minimum param-eter value (Pmin) and D is the seed bank after 15-yearsimulation. A large SI indicates that a small variation inthat parameter will result in a large modification in themodel output. A variation of ±40% of parameter valueswas considered.The first scenario simulated was the populationgrowth in the absence of herbicidal treatment. Then sev-eral individual tactics were simulated based on theannual application of herbicides at 50%, 75% and 100%of the standard rate. Experimental results obtained fromnumerous trials indicate that the level of P. brachys-tachys control achieved with commercial herbicidesapplied at standard rates (100%) presents a decreasepopulation size by 90% (Ticket, 1999). Our unpublishedresults, using the recommended rate of Clodinafop(Topik 24; full application rate 250 mL ha-1) at rate of50% and 75% resulted in 70% and 80% of reduction inpopulation of P. brachystachys, respectively.In absence of control measures, seed bank populationgrowth followed a logistic curve (Fig. 1). Under thistype of situation, seed bank density is projected to risefrom 100 seeds m-2 to 13,037 seed m-2 in less than twoyears and up to 21244 seed m-2 (1147 mature plants m-2) in a fifteen year period (Fig. 1). This can be consid-ered the carrying capacity of short-spiked canarygrassgrowing in association with wheat under this specifictype of conditions. The high potential growth is mainlydue to the high fecundity of this species. Our simulation results indicate that using full rate ofherbicide (90% efficiency), at the end of the 15-yr peri-od a population equilibrium of 15691 seed m-2 (42plants m-2) is reached in the seed bank (Fig. 1). Thisequilibrium position is only a 73.86% of the carryingcapacity of the system and, in practical terms, can beconsidered as a non-safe level. Reducing the efficacy ofthe herbicide to 70% or to 80% (by using 50% or 75%Modelling of the population dynamics of Phalaris brachystachys 157of the recommended application rates) results in seedbank reductions of 12.27% and 5.44% respectively (Fig.1). These results show, in the present case, the low her-bicide efficacy to reducing P. brachystachys popula-tions.The ranking of the sensitivity indices allowed forselection of the most important parameters (Table 1).The three demographic parameters that population sizewas most sensitive to were fecundity, seed bank mortal-ity and seed losses. As expected, the relatively high SIestimated for these three processes suggest that usingmanagement practices that reduce plant fecundityand/or increase seed loss and seed bank mortality mayresult in substantial changes in weed populations.In the model presented here information collectedfrom literature and field studies was integrated to sim-ulate the long-term dynamics of the annual weedspecies P. brachystachys under different levels of herbi-cide control. Simulation results confirm the difficultyin controlling this weed in continuous winter cerealproduction systems using agriculture practices that arePmax and Pmin are parameter values with an increase of ±40% on model parameters, respectively. See text for calculation of sensitivity index.ParametersValuesSensitivity indexPmax Pmin Model parameter Fecundity (f) 2036 872 1454 0.58Seed lost (p) 0.92 0.40 0.66 0.57Seed bank mortality (m) 0.70 0.30 0.50 0.44Emergence (g) 0.25 0.11 0.18 0.11Seedling survivorship (s) 0.42 0.18 0.30 0.01Table 1. Model parameters and sensitivity analysis for the model of Phalaris brachystachys life cycle05000100001500020000250001 2 3 4 5 6 7 8 9 10 11 12 13 14 15YearsSeedbankm-2Figure 1. Simulated seed bank of Phalaris brachystachystrends with herbicide applications at 0% (no herbicide) (),100% (), 75% () and 50% () of the recommended rateof herbicide application rate.commonly used in Southern Spain. Without control theseed bank population would reach an equilibrium levelat a density of 21,244 seeds m-2 after six years. Accord-ing to Cudney and Hill (1979), these infestation levelsare expected to result in yield losses greater than 60%in the crop and, therefore, they should be controlledbefore reaching these high levels. Annual application ofmost commercial herbicides at the standard rates(resulting 90% control) will not substantially reducethe long-term population equilibrium level. This resultagrees with farmers’ observation that, although mostgrass herbicides are apparently very effective in con-trolling P. brachystachys, weed populations remain rel-atively high year after year. Trying to reduce herbicideuse by reducing application rates resulted in partialcontrol of this weed but failed to reduce P. brachys-tachys populations. Most of these practices resulted inseed bank equilibrium levels between 15,691 and12,087 seeds m-2 (42 to 217 plants m-2) (Fig. 1). Theselevels are high enough to cause substantial yield losses(Afentouli and Eleftherohorinos, 1999). Moreover,annual application of herbicide is unsatisfactory foragronomic, economic and environmental reasons, as itresults in a relatively large annual investment in herbi-cides, an increased risk of development of herbicideresistant populations. Sensitivity analyses indicated that the seed bank ofP. brachystachys populations is particularly vulnerableto small changes in some demographic processes,namely fecundity, seed bank mortality and seed losses(Table 1). A thorough knowledge of the demographicparameters for which the model is particularly sensi-tive is needed in order to obtain accurate estimates ofthe corresponding demographic parameters. Conse-quently, further research should better estimate themaximum fecundity, seed bank mortality and seedlosses of P. brachystachys. Improving managementstrategies to target these parameters would be valuablein the control of this weed.The current model has highlighted the fact that her-bicide tactics currently in use were not able to stabilizeor decrease canarygrass populations in the crop sys-tem. In order to attain effective reductions of P.brachystachys populations, integration of herbicideapplications and agronomic practices would berequired. Crop rotation is a practice that can keepcanarygrass in check. Using a fallow year in the rota-tion is very effective in reducing wild oat populationsin winter wheat in Spain (Gonzalez-Andujar and Fer-nandez-Quintanilla, 1993). Consequently, furtherresearch should be addressed in the direction to findstrategies of integrated weed management (Mortensenet al., 2000) because they would be clues for the con-trol of this important weed.AcknowledgementsThe authors thank Dr. Jimenez-Hidalgo for his helpand data accessibility. This work was partially support-ed by FEDER funds and Ministerio de Educacion yCiencia project (R+D project AGF 2005-405). ReferencesAFENTOULI C.G., ELEFTHEROHORINOS I.G., 1999.Competition between wheat and canarygrass biotypes andtheir response to herbicides. Weed Sci 47, 55-61.BELL C.E., 1992. Littleseed canarygrass control in cerealgrains. Research Progress Report West Soc. Weed Sci.,Univ. California, Holtville, CA, USA. pp. 232-233. CATIZIONE P., VIGGIANI P., 1980. Un quadriennio diricerche sulle falaridi infestanti il grano. Atti GiornateFitopatologiche Supplemento 3, 257-311. [In Italian].CUDNEY D.W., HILL J.E., 1979. The response of wheatgrown with three population level of canarygrass to vari-ous herbicide treatments. Proc. West. Soc. Weed Sci. LasVegas, USA. pp. 55-56.DOYLE C.J., 1991. Mathematical models in weed manage-ment. Crop Prot 10, 432-444.GODINHO I., COSTA J.C.A., 1981. Concorrencia daPhalaris minor Retz. na cultura trigo. Proc. I CongressoPortugués de Fitiatria e de Fitofarmacologia e III Sympo-sium Nacional de Herbologia. Lisboa. Portugal. pp. 237-243. [In Portuguese].GONZALEZ-ANDUJAR J.L., FERNANDEZ-QUINTANI -LLA C., 1991. Modelling the population dynamics ofAvena sterilis under dry-land cereal cropping systems. JAppl Ecol 28, 1627.GONZALEZ-ANDUJAR J.L., FERNANDEZ-QUINTANI -LLA C., 1993. Strategies for the control of Avena sterilisin winter wheat production systems in central Spain. CropProt 12, 617-623.GONZALEZ-ANDUJAR J.L., SAAVEDRA M., 2003. Spa-tial distribution of annual grass weed populations in wintercereals. Crop Prot 22, 629-633. doi:10.1016/S0261-2194(02)00247-8.GONZALEZ-ANDUJAR J.L., FERNANDEZ-QUINTANI -LLA C., 2004. Modelling the population dynamics of158 L. Gonzalez Diaz et al. / Span J Agric Res (2009) 7(1), 155-159annual ryegrass (Lolium rigidum) under various weedmanagement systems. Crop Prot 23, 723-729. doi:10.1016/j.cropro.2003.12.007.GONZALEZ-ANDUJAR J.L., JIMENEZ-HIDALGO M.,GARCIA-TORRES L., SAAVEDRA M., 2005. Demogra-phy and population dynamic of the arable weed Phalarisbrachystachys (short-spiked canary grass) in winter wheat.Crop Prot 24, 581-584.HOLST N., RASMUSSEN I.A., BASTIAANS L., 2007.Field weed population dynamics: a review of modelapproaches and applications. Weed Res 47, 1-14.JIMENEZ-HIDALGO M.J., 1993. Incidencia y evolución delos alpistes (Phalaris spp.) en el trigo (Triticum sp.). Doc-toral thesis. University of Córdoba, Córdoba, Spain. [InSpanish].JIMENEZ-HIDALGO M.J., SAAVEDRA M., GARCIA-TORRES L., 1997. Phalaris brachystachys en cultivos decereales. In: Biología de las malas hierbas de España (SansX., Fernandez-Quintanilla C., eds). Ed Phytoma-España,Valencia, Spain. pp. 77-89.MORTENSEN D.A., BASTIAANS L., SATTIN M., 2000.The role of ecology in the development of weed manage-ment systems: an outlook. Weed Res 40, 49-62.PANNELL D.J., 1997. Sensitivity analysis of normative eco-nomic models: Theoretical framework and practical strate-gies. Agr Ecol 16, 139-152.SAGAR G.R., MORTIMER A.M., 1976. An approach to thestudy of the population dynamics of plants with specialreference to weeds. Adv Appl Biol 1, 1-47.TICKET B.R., 1999. Canarygrass control in wheat. 1999 For-age and Grain Report. College of Agriculture. Univ. Ari-zona, Tucson, USA.TORRAS J., GONZALEZ-ANDUJAR J.L., RECASENS J.,2008. Modelling the long term population dynamics ofpoppy (Papaver rhoeas) under various weed managementsystems. Weed Res 48, 136-146.Modelling of the population dynamics of Phalaris brachystachys 159

Short communication. Modelling of the population dynamics of Phalaris brachystachys Link under various herbicide control scenarios in a Mediterranean climate

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Short communication. Modelling of the population dynamics of Phalaris brachystachys Link under various herbicide control scenarios in a Mediterranean climate

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