The efficacy of glufosinate ammonium on ryegrass as influenced by different plant growth stages and different temperatures

Mucheri, Tendai (2016-12)

Thesis (MScAgric)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Herbicide resistance in weeds is the ability of weeds to survive and reproduce following exposure to the recommended dosage rate of herbicide that is lethal to its wild type. There is a widespread concern in agriculture about weeds with high genetic diversity that have developed resistance to weed control, ryegrass (Lolium spp.) included. Ryegrass has developed resistance to commonly used herbicides which include paraquat and glyphosate. There is an opportunity of using glufosinate ammonium to alleviate ryegrass weed resistance problems. The herbicide not only has a unique mode of action but also has no ryegrass resistance proven to it yet. There are restrictive application timings with glufosinate ammonium since it is a contact herbicide. More specific recommended dosage rates of herbicides can therefore be developed by determining the contribution of environmental factors and growth stage of weeds to efficacy of glufosinate ammonium. The principle objective of the study was to determine the effective dosage of glufosinate ammonium for the control of ryegrass weed under different temperatures and ryegrass growth stages. Studies on the influence of temperature on glufosinate ammonium efficacy are reported in Chapter 3, 4 and 7. Influence of ryegrass growth stage on efficacy of glufosinate ammonium is dealt with in Chapters 5 and 6. Glufosinate ammonium dosage rates of 0, 1.5, 3, 4.5, 6 and 7.5 L ha-1 were used for a temperature study in glasshouses running at 10/15, 15/20, 20/25, and 20/30 °C night/day temperatures. In Chapter 3 the influence of temperature on efficacy of glufosinate ammonium on young and mature ryegrass is described. Mature ryegrass was sprayed at 6 weeks while young ryegrass was sprayed at 3 weeks. The study proved that a low temperature of 10/15 °C controlled approximately 95% of both young and mature ryegrasses with 3 L ha-1 while the trend observed at 15/20 and 20/25 °C was irregular. Temperatures of 25/30 °C resulted in poor control of ryegrass. There was a general increase in control of young ryegrass as compared to mature ryegrass. In Chapter 4 the effect of temperature on efficacy of glufosinate ammonium with the added adjuvant ammonium sulphate (AMS) on ryegrass is described. Applied glufosinate ammonium dosage rates were 1, 2 and 3 L ha-1 with added ammonium sulphate at rates 1, 2 and 3%. Glasshouses were set at 10/15, 15/20, 20/25, and 20/30 °C night/day temperatures. The findings of the study indicated that a dosage rate of 3 L ha-1 glufosinate ammonium with addition of 2 and 3% ammonium sulphate controlled ryegrass effectively. There was more effective control of ryegrass with all concentrations of AMS at lower temperatures compared to the control at higher temperatures. An increase in AMS concentration resulted in an increase of ryegrass control at lower temperatures but this was not evident with control at higher temperature. Glasshouse and field experiments as described in Chapter 5 were conducted to determine the influence of different ryegrass growth stages on glufosinate ammonium efficacy. Glasshouse experiments were conducted at Welgevallen experimental farm and the field experiments were conducted at Welgevallen, Roodebloem and Langgewens experimental farms. Growth stages of ryegrass were 2, 4, 6, 8 and 10 weeks. Applied dosage rates were 1.5, 3, 4.5, 6 and 7.5 L ha-1 for glasshouse experiments and 2.5, 5, 7.5 and 10 L ha-1 for field experiments. The findings of the study proved that growth stage of ryegrass has no influence on efficacy of glufosinate ammonium. However, differences in control were observed for different glufosinate ammonium dosage rates. The study also revealed better control of ryegrass in the glasshouse as compared to the field. The trials described in Chapter 6 were conducted at Welgevallen experimental farm to investigate the efficacy of glufosinate ammonium with different added adjuvants on different aged ryegrass in both the glasshouse and the field. Three different growth stages of ryegrass (3, 6, and 9 weeks) were obtained by planting the ryegrass at 3-week intervals from the date the experiment was initiated, whilst young and mature growth stages were obtained in the field by spraying wild ryegrass at average leaf numbers of 6 and 15 leaves plant-1, respectively. In the glasshouse, control of 6-week old ryegrass was more effictive regardless of the mixture applied. Glufosinate ammonium with the added adjuvant (Velocity®) controlled ryegrass more effectively than glufosinate ammonium applied alone or with another added adjuvant (Summit Super). Field experiment results showed that AMS added to glufosinate ammonium controlled young ryegrass better than glufosinate ammonium alone and with the adjuvant (Ballista®). A glasshouse trial to compare efficacy of glufosinate ammonium on ryegrass and bahia grass species as influenced by temperature is described in Chapter 7. Applied dosage rates were 1.5, 3, 4.5, 6 and 7.5 L ha-1. The glasshouse temperatures were set at 10/15, 15/20, 20/25 and 25/30 °C night/day temperatures. The findings of the study showed a similar trend in glufosinate ammonium control of both grasses; as temperature increased, control decreased. At 10/15 and 15/20 °C temperatures percentage control was significantly higher than at 20/25 and 25/30 °C temperatures. Even though the trend was similar, mortality of ryegrass at high temperatures was more apparent as compared to bahia grass.

AFRKAANS OPSOMMING: Onkruiddoderweerstand is die vermoë van onkruide om te oorleef en voort te plant na toediening van die geregistreerde toedieningsdosis van ‘n onkruiddoder wat dodelik is vir die wilde ekotipe. Daar is wye kommer in landboukringe oor onkruide met hoë genetiese diversiteit wat weerstand teen chemiese onkruidbeheer ontwikkel het, raaigras (Lolium spp.) ingesluit. Raaigras het weerstand ontwikkel teen algemeen gebruikte onkruiddoders soos parakwat en glifosaat. Daar is ‘n geleentheid om glufosinaat ammonium te gebruik om probleme met onkruiddoderweerstand in raaigras te verlig. Die onkruiddoder het nie net ‘n unieke meganisme van werking nie maar daar is ook nog nie bewese weerstand teen dit in raaigras in Suid-Afrika gevind nie. Daar is beperkings ten opsigte van toedieningstydperke met glufosinaat ammonium aangesien dit hoofsaaklik ‘n kontakonkruiddoder is. Meer spesifieke aanbevole toedieningsdosisse van die onkruiddoder kan dus ontwikkel word deur die bydrae van omgewingsfaktore en groeistadia tot die effektiwiteit van glufosinaat ammonium vas te stel. Die hoofdoelwit van die studie was om die mees effektiewe toedieningsdosis van glufosinaat ammonium vir die beheer van raaigras onder verskillende temperatuurregimes en groeistadia te bepaal. Studies oor die invloed van temperatuur op glufosinaat ammonium effektiwiteit is uitgevoer in Hoofstukke 3, 4 en 7. Die invloed van groeistadia op effektiwiteit van glufosinaat ammonium is ondersoek in Hoofstukke 5 en 6. Glufosinaat ammonium toedieningsdosisse van 0, 1.5, 3, 4.5, 6 en 7.5 L ha-1 is gebruik vir ‘n temperatuurstudie in glashuise wat op 10/15, 15/20, 20/25 en 20/30 °C nag/dag temperature gestel was. In Hoofstuk 3 word die invloed van temperatuur op effektiwiteit van glufosinaat ammonium op jong en volwasse raaigrasplante beskryf. Die studie het gewys dat 3 L ha-1 glufosinaat ammonium sowat 95% beheer lewer op beide jong en volwasse raaigrasplante by ‘n temperatuur van 10/15 ºC terwyl die tendense by 15/20 en 20/25 nie duidelik was nie. By temperature van 25/30 ºC het swak beheer van raaigras voorgekom. Oor die algemeen is jong raaigras beter beheer as volwasse raaigras. In Hoofstuk 4 word die effek van temperatuur op die effektiwiteit van glufosinaat ammonium met bygevoegde ammoniumsulfaat (AMS) op raaigras beskryf. Glufosinaat ammonium is toegedien teen toedieningdosisse van 1, 2 en 3 L ha-1 tesame met AMS byvoegings van 1, 2 en 3%. Glashuise is ingestel op 10/15, 15/20, 20/25 en 20/30 °C nag/dag temperature. Die resultate het getoon dat ‘n toedieningsdosis van 3 L ha-1 glufosinaat ammonium met byvoeging van 2 en 3% AMS raaigras effektief beheer het. Daar was beter beheer van raaigras met byvoeging van al die AMS konsentrasies by laer temperature as by hoër temperature. ‘n Verhoging in AMS konsentrasie het gelei tot ‘n verhoging in raaigrasbeheer by laer temperature maar dit was nie sigbaar by hoër temperature nie. Glashuis- en veldproewe soos beskryf in Hoofstuk 5 is uitgevoer om die invloed van verskillende raaigras groeistadia op glufosinaat ammonium effektiwiteit te bepaal. Glashuis eksperimente is uitgevoer op Welgevallen proefplaas en veldeksperimente is uitgevoer op die Welgevallen, Langgewens en Roodebloem proefplase. Groeistadia van die raaigras wat getoets is was 2, 4, 6, 8 en 10 weke oue plante. Toedieningsdosisse was 1.5, 3, 4.5, 6 en 7.5 L ha-1 vir die glashuisproewe en 2.5, 5, 7.5 en 10 L ha-1 vir die veldproewe. Resultate van hierdie proewe het gewys dat groeistadium van raaigras geen effek op die effektiwiteit van glufosinaat ammonium gehad het nie. Verskille in vlakke van beheer is egter waargeneem tussen verskillende glufosinaat ammonium toedieningsdosisse. Die studie het egter ook beter beheer van raaigras in glashuisproewe gewys as in veldproewe. Die proewe wat in Hoofstuk 6 beskryf word het die invloed van verskillende bymiddels en raaigras groeistadia op die effektiwiteit van glufosinaat ammonium getoets in beide glashuis en veldproewe. Drie groeistadia van 3, 6 en 9 weke oue raaigrasplante is verkry deur die raaigrassaad met tussenposes van drie weke vanaf die aanvang van die proef in die glashuis te saai terwyl jong en meer volwasse plante in die veld gespuit is op twee verskillende stadia waarop die raaigras ongeveer 6 en 15 blare per plant onderskeidelik gehad het. In die glashuis was beheer van 6 weke oue plante baie beter ongeag die spuitmengsels wat toegedien is. Glufosinaat ammonium met Velocity® bygevoeg het raaigras beter beheer as glufosinaat ammonium sonder ‘n bymiddel of met byvoeging van Summit Super®. Die veldproef het getoon dat glufosinaat ammonium met bygevoegde AMS (2%) jong raaigras beter beheer het as glufosinaat ammonium alleen of met Ballista® bygevoeg. ‘n Glashuisproef wat die effektiwiteit van glufosinaat ammonium teen verskillende temperature op raaigras en bahiagras ondersoek het, word in Hoofstuk 7 beskryf. Toedieningsdosisse was 1.5, 3, 4.5, 6 en 7.5 L ha-1. Die glashuistemperature was gestel op 10/15, 15/20, 20/25 en 25/30 °C nag/dag temperature. Die resultate wys soortgelyke neigings in terme van glufosinaat ammonium beheer vir beide spesies naamlik dat die beheer afneem soos temperature toeneem. Teen 10/15 en 15/20 ºC was beheer betekenisvol hoër as by 20/25 en 25/30 ºC. Alhoewel die neigings eenders was, was beheer van raaigras by hoër temperature swakker as beheer van bahiagras.

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