Call number: LD2668 .T4 1965 S859 / Master of Science

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Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Glufosinate ammonium is one of the most widely-applied broad-spectrum herbicides, controlling weeds in a huge variety of crops worldwide. Farmers rely on glufosinate ammonium because it ensures a high degree of crop safety, as it only affects the parts of the plant where it is applied. It is effective against a broad range of weeds, eliminating the need to apply several herbicides to control different weeds in a given crop. Its unique mode of action makes it ideal to be used in rotation with other herbicides to mitigate weed resistance. Despite these favourable attributes for weed control glufosinate ammonium has its shortcomings. Glufosinate ammonium is a post emergence herbicide and its efficacy is not exempt from the effect of environmental/climatic conditions and the growth stage of weeds. The possible effect of these factors on the performance of the herbicide was investigated in a glasshouse study using ryegrass (Lolium spp) as the test species. The investigation consisted of four experiments. The first two experiments investigated the effect of applying different doses of glufosinate ammonium to commercial ryegrass and weedy ryegrass seedlings at different growth stages in a glasshouse. The glufosinate ammonium dosage rates were 0, 2.5, 5, 7.5 and 10 L ha-1. The findings of the studies showed that neither plant age nor herbicide rate affected the efficacy of glufosinate ammonium in a commercial cultivar or weedy type ryegrass. There were no statistically significant differences between the percentage mortality caused by any of the glufosinate ammonium dosage rates between 2.5 and 10 L ha-1 with the percentage control being higher than 90% at all dosage rates in both experiments. The objective of the third and fourth experiment was to determine the effect of temperature on the efficacy of ryegrass control by glufosinate ammonium. The temperatures for the third experiment were 10/15 0C (cool) and 15/20 0C (warm) night/day and for the fourth experiment 10/15 0C (cool) and 20/25 0C (warm) night/day. The glufosinate ammonium dosage rates applied were 0, 2.5, 5, 7.5 and 10 L ha-1. Plants in the third experiment remained in the glasshouse throughout the study at a constant temperature regime. Under cool temperatures glufosinate ammonium controlled ryegrass plants, irrespective of the rate applied, with 100% control achieved at a dosage rate of 2.5 L ha-1. This was not the case under warm temperatures where 100% control was not even achieved at the 10 L ha-1 dosage rate. In the fourth experiment cool and warm temperature regimes were applied before and after spraying. The four temperature treatments applied were therefore cool (10/15 ºC), warm (20/25 ºC), cool/warm (where the plants were moved from the cool temperature to the warm one after spraying) and warm/cool (which was the opposite of cool/warm). The results observed from the fourth experiment followed the same trend as in experiment three. Ryegrass plants that were grown under warm temperature and moved to cool temperature after spraying were better controlled than under cool/warm temperatures. Dosage rates of 2.5 L ha-1 gave 95% control of ryegrass under cool temperatures whereas the same dosage rate only achieved about 55% control under warm temperatures. Glasshouse and field trials were conducted at Stellenbosch University experimental farm Welgevallen (33°56’S, 18°42’E) to investigate the effect of the additive ammonium sulphate (AMS) on the efficacy of glufosinate ammonium. The glasshouse trial consisted of four ryegrass populations (one commercial cultivar (Lolium multiflorum cv Agri Hilton) and three suspected resistant weedy types (Lolium spp.) The temperature of the glasshouse was 20/25 0C night/day. The four ryegrass populations were each subjected to an experiment using a 7 x 2 factorial design with seven dosage rates (0, 0.75, 1.5, 3, 4.5, 6 and 7.5 L ha-1 of glufosinate ammonium) and two AMS treatments (with and without AMS) laid out in a randomized complete block design with three replicates. The AMS increased the efficacy of glufosinate ammonium on the commercial cultivar and resistant population 2 at certain critical dosage rates. The field trials were conducted in 2013 and 2014. The trials were arranged factorially in a randomised complete block design replicated four times. The treatment factors were two treatments (glufosinate ammonium alone and glufosinate ammonium plus AMS) and five glufosinate ammonium rates (0, 2.5, 5, 7.5, and 10 L ha-1 of glufosinate ammonium). Ammonium sulphate (10 g) was diluted in 1 L of distilled water before mixing with glufosinate ammonium. The findings of the study revealed that AMS increased the efficacy of glufosinate ammonium under field conditions in 2013 but not in 2014. Experiments with the aim of determining the effect of propyzamide on the efficacy of four herbicides (atrazine, glufosinate ammonium, glyphosate and imazamox) was carried out in a glasshouse as well as in field studies. In the glasshouse study, ryegrass was used as a test species. The four herbicides and propyzamide were applied separately, followed by mixtures with propyzamide at the rates of 0, 0.5, 0.75 and 1x (times the recommended rate) for each of the herbicides in the mixture. Results suggest that propyzamide negatively affected atrazine efficacy on ryegrass in the glasshouse but not the efficacy of any other herbicides. Field experiments were conducted to determine the effect of adding propyzamide to the four herbicides on the efficacy and residual action of the herbicides in 2012, 2013 and 2014. Field trials were conducted at Welgevallen, Roodebloem and Langgewens experimental farms. The experimental design was a randomised complete block with nine treatments replicated four times. Propyzamide increased the efficacy of atrazine in some of the field trials as well as the efficacy of imazamox in some trials but generally the results were variable and propyzamide also did not enhance the residual action of the herbicides in most of the trials / AFRIKAANSE OPSOMMING: Glufosinaat ammonium is een van die mees algemene breëspektrum nie-selektiewe onkruiddoders wat onkruide in ‘n groot verskeidenheid gewasse wêreldwyd beheer. Boere maak staat op glufosinaat ammonium omdat dit redelik veilig vir die gewas is as gevolg van die feit dat dit slegs die gedeelte van die plant waarmee dit in aanraking kom, affekteer. Dit is effektief teen ‘n wye verskeidenheid van onkruide wat dit onnodig maak om verskeie onkruiddoders te gebruik om verskillende onkruide in ‘n gewas te beheer. Die unieke meganisme van werking maak dit ideaal om in afwisseling met ander onkruiddoders te gebruik om onkruiddoderweerstand te bestuur. Ten spyte van al hierdie voordele het glufosinaat ammonium ook verskeie tekortkominge. Glufosinaat ammonium is ‘n na-opkoms onkruiddoder en sy effektiwiteit word beïnvloed deur omgewings- of klimaatstoestande en die groeistadia van onkruide. Die moontlike invloed van bogenoemde faktore op die effektiwiteit van glufosinaat ammonium is in ‘n glashuisstudie ondersoek waar raaigras (Lolium spp) as toetsspesie gebruik is. Die ondersoek het uit vier eksperimente bestaan. Die eerste twee eksperimente het die effek van verskillende toedieningsdosisse van glufosinaat ammonium op raaigrassaailinge van ‘n kommersiële kultivar asook ‘n onkruidbiotipe op verskillende groeistadia ondersoek. Die glufosinaat ammonium dosisse was 0, 2.5, 5, 7.5 en 10 L ha-1. Die resultate het getoon dat nie die toedieningsdosis of die plantgroeistadium die effektiwiteit van glufosinaat ammonium op die kommersiële raaigras kultivar of die onkruid biotipe beïnvloed het nie. Daar was nie enige statisties betekenisvolle verskille tussen die persentasie mortaliteit veroorsaak deur enige van die glufosinaat ammonium dosisse tussen 2.5 en 10 L ha-1 nie en die persentasie beheer was hoër as 90% by alle toedieningsdosisse in beide populasies. Die derde en vierde eksperimente is gedoen om vas te stel of temperatuur ‘n rol speel in die effektiwiteit van glufosinaat ammonium op raaigras beheer. Die temperature vir die derde glashuisproef was gestel op 10/15 ºC (koel) en 15/20 ºC (warm) nag/dag temperature en vir die vierde glashuisproef was dit 10/15 ºC (koel) en 20/25 ºC (warm). Die glufosinaat ammonium toedieningsdosisse was 0, 2.5, 5, 7.5 and 10 L ha-1. Die plante in die derde eksperiment het in die onderskeie glashuise by dieselfde temperatuur gebly deur die loop van die hele eksperiment. Onder koel toestande het glufosinaat ammonium die raaigrassaailinge 100% beheer selfs by die laagste toedieningsdosis van 2.5 L ha-1 en by alle dosisse bo dit. By warmer temperature egter, kon selfs die hoogste dosis van 10 L ha-1 nie 100% beheer behaal nie. Die vierde eksperiment was soortgelyk aan die derde eksperiment behalwe dat die koel en warmer temperature afgewissel is voor en na die plante bespuit is. Die vier temperatuurbehandelings was dus koel (10/15 ºC), warm (20/25 ºC), koel/warm (waar die plante na spuit van die koel na die warm glashuis verskuif was) en warm/koel (die teenoorgestelde van die koel/warm behandeling). Die resultate wat waargeneem is het dieselfde tendens getoon as die resultate van die derde eksperiment. Toedieningsdosisse van 2.5 L ha-1 het 95% beheer van raaigras wat onder koel toestande gegroei het getoon terwyl dieselfde dosis onder die warm toestande slegs 55% beheer behaal het. Glashuis- en veldproewe is uitgevoer op die Welgevallen proefplaas van die Universiteit van Stellenbosch (33°56’S, 18°42’O) om die invloed van die byvoeging van ammoniumsulfaat (AMS) op die effektiwiteit van glufosinaat ammonium te ondersoek. In die glashuisproef was vier populasies raaigras (een kommersiële kultivar Lolium multiflorum cv Agri Hilton) en drie vermoedelik weerstandbiedende onkruidpopulasies (Lolium spp) gebruik. Die temperatuur van die glashuis was op 20/25 0C nag/dag ingestel. Die vier raaigras populasies was elk blootgestel aan ‘n faktoriaal gereëlde 7 x 2 eksperiment met sewe toedieningsdosisse (0, 0.75, 1.5, 3, 4.5, 6 en 7.5 L ha-1 glufosinaat ammonium) en twee AMS behandelings (met en sonder AMS) wat in ‘n volledige ewekansige blokontwerp met drie herhalings uitgelê is. Die AMS het die effektiwiteit van glufosinaat ammonium slegs op die kommersiële kultivar en een van die vermoedelik weerstandbiedende populasies verhoog by ‘n sekere kritiese toedieningsdosis. Die veldproewe is in 2013 en 2014 uitgevoer. Die proewe is faktoriaal uitgelê in ‘n volledig ewekansige blokontwerp wat vier keer herhaal is. Die behandelingsfaktore was twee behandelings (glufosinaat ammonium met en sonder AMS) en vyf glufosinaat ammonium toedieningsdosisse (0, 2.5, 5, 7.5, en 10 L ha-1 glufosinaat ammonium). Die AMS (10 g) is in 1 L gedistilleerde water opgelos voordat dit met die glufosinaat ammonium oplossing vermeng is. Die resultate het getoon dat die AMS die effektiwiteit van glufosinaat ammonium onder veldtoestande slegs in 2013 betekenisvol verbeter het maar nie in 2014 nie. Proewe met die doel om die effek van propisamied op die effektiwiteit van vier onkruiddoders (atrasien, glufosinaat ammonium, glifosaat en imasamoks) te bepaal is uitgevoer in die glashuis sowel as in die veld. In die glashuisstudie is die onkruiddoders op raaigras saailinge toegedien. Die vier onkruiddoders en propisamied is alleen toegedien en dan is elk van die vier onkruiddoders ook gemeng met propisamied teen die toedieningsdosisse van 0, 0.5, 0.75 en 1.0 keer die aanbevole dosis (x) van elk van die bestanddele van die mengsel. Die resultate dui aan dat propisamied die werking van atrasien op raaigras negatief beïnvloed het maar nie die werking van enige van die ander onkruiddoders nie. Veldeksperimente is uitgevoer om die effek van propisamied op die effektiwiteit en residuele aksie van die onkruiddoders onder veldtoestande in 2012, 2013 en 2014 te bepaal. Die veldproewe is uitgevoer op die Welgevallen, Langgewens en Roodebloem proefplase. Die proefontwerp was ‘n volledig ewekansige blokontwerp met nege behandelings wat vier keer herhaal is. Propisamied het die effektiwiteit van atrasien in sekere lokaliteite verbeter asook die van imasamoks in sekere proewe maar die resultate was oor die algemeen wisselvallig. Byvoeging van propisamied by die onkruiddoders het in die meeste gevalle nie die residuele werking daarvan verbeter nie.

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