The financial and managerial implications of herbicide resistance of annual ryegrass in the Central Swartland

Spammer, Zander (2018-03)

Thesis (MCom)--Stellenbosch University, 2018.

Thesis

ENGLISH SUMMARY : Food security is under increased pressure due to the demands set by a growing global population. Farming, the sector primarily responsible for food security, experiences this growing pressure directly. Because arable land is fixed in absolute terms, production levels of available arable land need to increase by optimising yields. To achieve optimal crop yields the yield reducing factors have to be identified and managed to limit impact on production. Amongst the various yield limiting factors, one of the most important are weeds. This study focuses on winter cereal farming in the Central Swartland area of the Western Cape Province. In this area annual ryegrass has the most significant negative effect on production. This resulted in farmers becoming heavily reliant on the use of herbicides to effectively control ryegrass. This reliance on herbicides together with mal practises regarding the application of herbicides caused ryegrass to develop herbicide resistance. Herbicide resistance can lead to an increase in the cost of weed control, a decrease in potential income, a reduction in the number of possible crops that can be produced and a decrease in the value of the land. There are various methods to manage and prevent herbicide resistance which are discussed in this study, but the primary conclusion is that various methods of control such as chemical, physical and biological control have to be integrated into a producer’s complete weed management program. The detrimental effect of herbicide resistant ryegrass on the profitability of a winter cereal farm in the Central Swartland are researched on a per hectare basis in this study and forms the central focus of this study. A well-known simulation model, the Resistance Integrated Management model (RIM model), is used to simulate three different scenarios. A multi group discussion was held to verify and validate the parameters and assumptions needed to use this model in the Central Swartland. The three scenarios simulated in this study were: no resistance; known resistance (glyphosate and paraquat) and an unknown resistance (trifluralin). In both scenarios where resistance was simulated, a worst-case scenario was assumed, in other words zero percentage control. The gross margin per hectare for wheat monoculture (wheat-wheat-wheat-wheat) decrease from R2 488/ha to R329/ha after the effects of the resistance. With exception of the wheat and medic rotation, the known resistance decreased the gross margin by a minimum of 15% over a ten year period for all the other crop rotations. The unknown resistance decreased some of the crop rotations’ gross margins detrimentally, the wheat monoculture system decreased by 86% and the wheat-wheat-wheat-canola and wheat-wheat-wheat-legumes by 67% and 66% respectively. The wheat and canola rotation system were found to be the most profitable in both the no resistance and the known resistance scenarios. The wheat and medics rotation system achieved the highest level of control in all three scenarios as well as achieving the highest gross margin per hectare in the unknown resistance scenario.

AFRIKAANSE OPSOMMING : Voedselsekerheid is toenemend onder druk as gevolg van die eise wat ‘n groeiende wêreldbevolking stel. Hierdie druk word direk deur die landbousektor, primêr verantwoordelik vir die handhawing van voedselsekerheid, ervaar. Omdat bewerkbare landbougrond in absolute terme beperk is, is dit noodsaaklik dat produksie op beskikbare grond optimale opbrengste lewer. Ten einde optimale oeste te lewer moet die faktore wat opbrengste beperk geïdentifiseer en korrek bestuur word. Die produksie van gewasse word deur verskeie faktore beperk waarvan gras onkruide een van die belangrikste is. Hierdie studie fokus op wintergraanverbouïng in die Sentrale Swartland van die Wes-Kaap Provinsie. In hierdie area het eenjarige raaigras die grootste negatiewe uitwerking op opbrengste. Die gevolg is dat landbouers toenemend steun op chemiese onkruiddoders in ‘n poging om raaigras te beheer. Die toenemende afhanklikheid van onkruiddoders tesame met die verkeerde toediening daarvan het gelei daartoe dat raaigras weerstandigheid teen onkruiddoders ontwikkel het. Weerstand teen onkruiddoders mag lei tot ‘n toename in die koste van onkruidbeheer, ‘n verlies in potensiële inkomste, ‘n afname in die verskeidenheid gewasse wat verbou kan word asook ‘n afname in die waarde van die grond. Die verskeie metodes beskikbaar om weerstand teen onkruiddoders te bestuur en te voorkom word in hierdie studie bespreek. Die primêre gevolgtrekking is dat hierdie metodes, nl. chemiese, fisiese en biologiese kontrole, in ‘n produsent se bestuursprogram geïntegreer moet word ten einde ‘n volledige onkruidbeheerprogram te bewerkstellig. Die skadelike gevolg van weerstandige raaigras op die winsgewendheid van ‘n wintergraan plaas in die Sentrale Swartland word op ‘n per hektaar basis nagevors en vorm die fokus van hierdie studie. ‘n Welbekende simulasie model, nl. die ‘Resistance Integrated Management model’ (RIM model) word gebruik om drie verskillende scenarios na te boots. ‘n Bespreking tussen verskeie rolspelers in die bedryf is gehou om die parameters en aannames nodig om die model in die Sentrale Swartland te gebruik, te verifieer en te bekragtig. Die drie scenarios in hierdie studie gebruik, is: geen weerstand; bekende weerstand (glifosaat en paraquat); en ‘n onbekende weerstand (trifluralin). In beide scenarios waar weerstandigheid nageboots is, is die veronderstelling van weerstandigheid in die ergste graad, dus geen persentasie van kontrole, aanvaar. Die bruto marge per hektaar in die geval van koring monokultuur (koring-koring-koring-koring) het van R2 488/ha na R329/ha afgeneem as gevolg van die effek van weerstand. Met uitsondering van die koring en medic rotasie, het bekende weerstandigheid bruto marges teen ‘n minimum van 15% oor ‘n tienjaar periode laat afneem in al die ander gewas rotasies wat bestudeer is. Onbekende weerstandigheid het sommige van die gewas rotasies se bruto marges uiters nadelig beïnvloed. Die koring monokultuur het ‘n afname van 86% getoon terwyl die koring-koring-koring-canola en die koring-koring-koring-peulgewasse afnames van onderskeidelik 67% en 66% getoon het. Die koring en canola rotasie was die mees winsgewende sisteem in beide die geen weerstand en die bekende weerstand scenarios. Die koring en medics rotasie het die hoogste vlak van kontrole in al drie scenarios getoon asook die hoogste bruto marge per hektaar in die geval van onbekende weerstand behaal.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103468
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