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

[摘要] 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.

[发布机构] Stellenbosch University